TACACS+

1. Introduction

tac_plus is a TACACS+ daemon. It provides Cisco Systems routers and access servers with authentication, authorisation and accounting services.

This version is a major rewrite of the original Cisco source code. Key features include:

• NAS specific host keys, prompts, enable passwords

• NAS- and ACL-dependent group memberships

• Flexible external backends for user profiles (e.g. via PERL scripts or C; LDAP (including ActiveDirectory), RADIUS and others are included)

• Connection multiplexing (multiple concurrent NAS clients per process)

• Session multiplexing (multiple concurrent sessions per connection, single-connection)

• Scalable, no limit on users, clients or servers

• CLI context aware. At the time of writing this, no other TACACS+ daemon is.

• Both IPv4 and IPv6 are fully supported.

• Compliant to latest TACACS+ protocol specification (draft 1.78)

2. Definitions and Terms

The following chapters utilize a couple of terms that may need further explanation:

Since a NAS is sometimes referred to as a server, and a daemon is also often referred to as a server, the term server has been avoided here in favor of the less ambiguous terms NAS and Daemon.

3. Operation

This section gives a brief and basic overview how to run tac_plus.

In earlier versions, tac_plus wasn't a standalone program but had to be invoked by spawnd. This has changed, as spawnd functionality is now part of the tac_plus binary. However, using a dedicated spawnd process is still possible and, more importantly, the spawnd configuration options and documentation remain valid.

tac_plus may use auxilliary MAVIS backend modules for authentication and authorization.

tac_plus [ -P ] [ -d level ]  [ -i child_id ] configuration-file [ id ]

#!/usr/local/bin/tac_plus
id = spawnd {
    listen = { port = 49 }
    listen = { port = 4949 }
    # see the spawnd configuration guide for further configuration options
}

id = tac_plus {
    accounting log = /var/log/tac_plus/%Y/%m/%d.log
    retire limit = 1000
    mavis module = external {
        exec = /usr/local/lib/mavis_tacplus.pl
        # see the MAVIS configuration manual for more options and other modules
    }
    login backend = mavis

    host = world {
        prompt = "\nHitherto shalt thou come, but no further. (Job 38.11)\n\n"
        key = QaWsEdRfTgY
        enable 15 = clear test
        address = 0.0.0.0/0
    }

    group = readwrite {
        default service = permit
        service = shell {
            default command = permit
            set priv-lvl = 15
        }
    }

    group = getconfig {
        default service = permit
        service = shell {
            set autocmd = "sho run"
            set priv-lvl = 15
        }
    }

    user = marc {
       login = crypt $1$xxxxxxxx$hDZPHghXe8XvoHeFdqUwm/
       member = readwrite@world
       member = getconfig@192.168.0.0/16
    }
}

4. TACACS+ Configuration Syntax

All the configuration directives below need to be enclosed within a

id = tac_plus { ... }

section.

	Comments in Configuration Files
	Comments can appear anywhere in the configuration file, starting with the # character and extending to the end of the current line. Should you need to disable this special meaning of the # character, e.g. if you have a password containing a # character, simply enclose the string containing it within double quotes.

The recommended order for writing a configuration file is

1. global definitions

2. hosts

3. timespecs

4. acls

5. groups

6. users

---

4.2. Configuring Hosts

The daemon will talk to known hosts only and reject connections from unknown ones.

If you want tac_plus to encrypt its packets (and you almost certainly do want this, as there can be usernames and passwords contained in there), then you'll have to specify an (non-empty) encryption key. The identical key must also be configured on any NAS which communicates with tac_plus.

To specify a global key, use a statement similar to

host = 0.0.0.0/0 {
    key = "your key here"
}

or, alternatively,

host = world {
    key = "your key here"
    address = 0.0.0.0/0
}

(where world is not a keyword, but just some arbitrary character string).

Double Quotes

You only need double quotes on the daemon if your key contains spaces. Confusingly, even if your key does contain spaces, you should never use double quotes when you configure the matching key on the NAS. The daemon will reject connections from hosts that have no encryption key defined. Double quotes within double-quoted strings may be escaped using the backslash character \ (which can be escaped by itself), e.g.: key = "quo\\te me\"." translates to the ASCII sequence quo\te me".

Any CIDR range within a host definition needs to to be unique, and the most specific definition will match. The requirement for unambiguousness is quite simply based on the fact that certain host object attributes (key, prompt, enable passwords) may only exist once.

On the NAS, you also need to configure the same key. Do this by issuing:

aaa new-model
tacacs-server host 192.168.0.1 single-connection key your key here

The optional single-connection parameter specifies that multiple sessions may use the same TCP/IP connection to the server.

Generally, the syntax for host declarations conforms to

host = [ realm realm ] name_or_ip-range { key-value pairs }

The optional realm tells the daemon to use the definition only for connections with a corresponding spawnd realm. For example,

id = spawnd { listen = { port = 49 } listen = { port = 4949 realm = somevendor } }
id = tac_plus {
    host world = { address = ::0/0 ... }
    host realm somevendor weirdrouters = { address = :0/0 ... }
    group adminA = { ... }
    group adminB = { ... }
    user = marc { member = adminA member = AdminB@weirdrouters }
}

makes group membership dependent on the address and/or port the NAS uses to contact the TACACS+ server. User marc will be a member of group adminA for network access servers connecting via port 49, and member of adminB for those using port 4949.

Hosts can be refered to by IP address or (with some exceptions) by name.

The key-value pairs permitted in host sections of the configuration file are

• key = string

  As mentioned before, this sets the key used for encrypting the communication between server and NAS.

  During debugging, it may be convenient to temporarily switch off encryption by using an empty key:

  key = ""
  

  Be careful to remember to switch encryption back on again after you've finished debugging.

• client-only = ( yes | no )

  For client-only = yes, this host declaration will be used as a NAC address (range/group) only. TACACS+ sessions originating from IP adresses matching this object will be refused.

  By default, this setting is inherited from a super-net and to all sub-networks. If set to yes, no TACACS+ session requests are permitted from IP addresses matching the object.

• inherit = ( yes | no )

  If set to no, the current host declaration won't inherit configuration snippets (e.g.: key, enable passwords) from its supernet. Default is yes.

• connection timeout = s

  Terminate a connection to this NAS after an idle period of at least s seconds.

• name = string

  Assigns the name string to the host object. This, combined with the address keyword), may be used to form host groups. Don't use this attribute if you've already asigned a name after the initial host = statement, and take care to define hosts before users and groups, or group membership assignments may fail silently.

• prompt = string

  Set the initial log-in prompt to string.

• enable [ level ] = ( permit | deny | login | ( clear | crypt) password )

  This directive may be used to set host specific enable passwords, to use the login or to permit (without password) or refuse any enable attempt. Enable secrets defined here have a lower precedence than those defined at user- or group-level. level defaults to 15.

  	Password Hashes
  	You can use the openssl passwd utility to compute password hashes. For example, openssl passwd -1 clear_text_password returns a MD5 hash, while openssl passwd -crypt clear_text_password returns a DES hash. DES passwords are by design truncated to eight characters.

  You can enable via TACACS+ by configuring on the NAS:

  aaa authentication enable default group tacacs+ enable
  

• template = ( address | name )

  This uses part of an existing host definition for address or name as template for the current host declaration. Only prompt, key, enable passwords and content are copied, and no recursive lookups take place.

• address = cidr

  Adds the address range specified by cidr to the current host definition.

  

• address file = file

  Add the addresses from file to the current host definition. Shell wildcard patterns are expanded by glob(3).

• password ( max-attempts = integer | backoff = seconds )

  The max-attempts option sets the maximum number of Password: prompts per session. Likewise, backoff specifies the (host-specific) delay before returning a Password incorrect. message and closing the session.

  Setting these parameters here overrides the corresponding global options, which come with a more exhaustive explanation.

  backoff can be specified for both NAC and NAS host objects. If both are given, the smaller one wins.

• anonymous-enable = ( permit | deny )

  Several broken TACACS+ implementations send no or an invalid username in enable packets. Setting this option to deny enforces user authentication before enabling. Setting this option here has precedence over the global option.

• user = name

  This directive sets a default user name for connections sourced from hosts matching this host object. For example:

  host = nms { address = 1.2.3.4 user = nmsuser }
  

  will tell the daemon not to query for the user name for connections coming from 1.2.3.4, but to use nmsuser instead.

  Use this option with care. It may come handy while transitioning to a TACACS+ environment, but has several severe implications, the first one being that the router has no idea about the username, which implies that authorization via TACACS+ won't work.

• dns reverse-lookup = ( yes | no )

  NAC ACLs support matching against the clients DNS reverse-lookup. Using this directive enables or disable NAC DNS lookups for the IP addresses in the host group.

• single-connect ( may-close ) = ( yes | no )

  This directive may be used to permit or deny the single-connection feature for a particular host object. The may-close keyword tells the daemon to close the connection if it's unused.

---

4.2.1. Inheritance and Hosts

For host lookups, the daemon looks for the most specific host definition first. If that definition (or the requested value) doesn't exist, it looks for the next less-specific one. This process continues through the entire (IPv6) CIDR hierarchy, until a match is found.

In other words: For host parameters, the most specific host definition with that parameter defined matches.

For example, if a host 192.168.1.15 connects to the server, the server needs to know which encryption key to use.

In IPv6-mapped CIDR notation (which the daemon uses internally), the IPv4 CIDR range

192.168.1.15/32

equals

0000:0000:0000:0000:0000:FFFF:C0A8:010F/128

The daemon will search for a key in the host definition for 192.168.1.15 and the (defined) supernets:

0000:0000:0000:0000:0000:FFFF:C0A8:010F/128
0000:0000:0000:0000:0000:FFFF:C0A8:010F/127
0000:0000:0000:0000:0000:FFFF:C0A8:010E/126
0000:0000:0000:0000:0000:FFFF:C0A8:010C/125
...
0000:0000:0000:0000:0000:FFFF:C000:0000/98
0000:0000:0000:0000:0000:FFFF:8000:0000/97
0000:0000:0000:0000:0000:FFFF:0000:0000/96
0000:0000:0000:0000:0000:FFFE:0000:0000/95
0000:0000:0000:0000:0000:FFFC:0000:0000/94
...
0000:0000:0000:0000:0000:0000:0000:0000/3
0000:0000:0000:0000:0000:0000:0000:0000/2
0000:0000:0000:0000:0000:0000:0000:0000/1
0000:0000:0000:0000:0000:0000:0000:0000/0

The first key found will be used, as it is the most specific one.

By default, prompt, key, enable, anonymous-enable and content specifications are inherited. Inheritance may be switched off for a host object:

    inherit = no

---

4.2.2. Railroad Diagrams

---

4.2.3. Example

host = 10.0.0.0/8 {
    name = customer1
    key = "your key here"
    prompt = "\nHitherto shalt thou come, but no further. (Job 38.11)\n\n"
    enable 15 = clear whatever
}

host = test123 {
    address = 10.1.2.0/28
    address = 10.12.1.30/28
    address = 10.1.1.2
    # key/prompt/enable will be inherited from 10.0.0.0/8 by default,
    # unless you specify "inherit = no"
    address file = /some/path/test123.cidr
    prompt = "\nGo away.\n\n"
}

# Working hours are from Mo-Fr from 9 to 16:59, and
# on Saturdays from 9 to 12:59:
timespec = workinghours {
    "* 9-16 * * 1-5"   # or: "* 9-16 * * Mon-Fri"
    "* 9-12 * * 6"     # or: "* 9-12 * * Sat"
}

timespec = sunday { "* * * * 0" }

timespec = example {
    Wk2305-0855,Sa,Su2305-1655
    Wk0905-2255,Su1705-2255
    Any
}

acl = myacl {
    nac = 10.0.0.0/8
    nac = 11.0.0.0/8
    nas = somehostobjectname
}

acl = myacl {
    time = workinghours
}

    acl script = myacl123 {
        if (nas == 1.2.3.4 || nac = SomeHostName || nac-dns =~ /\\.example\\.com$/) deny
    }
    user = joe {
        service = shell {
            script = myacl123 { if (cmd =~ /^(no\s)?shutdown\s/) permit }
        }
    }

---

4.6. Configuring Users and Groups

A user may be member of a group (also known as role or profile). Actual group membership may depend on various factors, e.g. the NAS the user is on, the NAC or time ranges. Each group may in turn be member of another group and so on ad infinitum.

User and group declarations are pretty similar. The major difference is, that groups are static, while user declarations may be added at run-time via the MAVIS back-end.

The basic form of a user and group declarations is:

user = string { ...  }

or, respectively for groups:

group = string {  ...  }

The curly brackets may contain key-value pairs and service declarations.

The following declarations are valid in user context only:

• login = ( ( clear | crypt ) password | mavis )

  The login password authenticates SHELL log-ins to the server.

  login = crypt aFtFBT4e5muQE
  login = clear Ci5c0
  

  For crypt, DES- or MD5-hashed passwords may be used.

  If the mavis keyword is used instead, the password will be looked up via the MAVIS backend. It will not be cached. This functionality may be useful if you want to authenticate at external systems, despite static user declarations in the configuration file.

• pap = ( ( clear | crypt ) password | mavis )

  The pap authenticates PAP log-ins to the server. Just like with login, the password doesn't need to be in clear text, but may be DES (or MD5) hashed, or may be looked up via the MAVIS backend.

• arap = clear password

  For ARAP authentication, a cleartext password is required.

• chap = clear password

  For CHAP authentication, a cleartext password is required.

• ms-chap = clear password

  For MS-CHAP authentication, a cleartext password is required.

• opap = clear password

  For outgoing PAP authentication, a cleartext password is required.

• password = clear password

  This directive sets all previously undefined passwords (with the exception of OPAP) to the given cleartext password. This directive is retained for backwards compatibility only, and usage is deprecated.

The following key-value pairs are valid in both user and group context:

• acl = ( [ permit ] | deny ) [ not ] acl

  Validity of of a user or group profile may be restricted by ACLs. Multiple ACLs may be specified and are evaluated in order.

• valid from = ( YYYY-MM-DD | s )

  The profile will be valid starting at the given ISO8601 date, which can be specified either in ISO8601 date format or as in seconds since January 1, 1970, UTC.

• valid until = ( YYYY-MM-DD | s )

  The profile will be invalid after the given date.

• message = string

  A message displayed to the user upon log-in.

• member [ acl [ not ] acl ] = string

  This directive defines group membership, optionally depending on the NAS server's address or on some access list. For example, you could configure:

  host = campus { ... }
  host = remote { ... }
  host = router { ... }
  timespec = workinghours { ... }
  group = admins { ... }
  group = staff { ... }
  group = guest { ... }
  

  plus a couple of ACLs:

  acl oncampus = { nac = campus }
  acl viavpn = { nac = remote }
  acl atwork = { nac = campus time = workinghours }
  

  and then base group membership on the latter:

  user = adminuser { member = admins }
  user = employee {
      ...
      member acl atwork = staff@router
      member acl viavpn = staff
      member acl remote = guest
      ...
  }
  user = guest {
      ...
      member acl atwork = guest
      ...
  }
  user = myself {
      ...
      member = admins@router
      member = staff
      ...
  }
  

  member directives are to be ordered by ACL name, with definitions without ACL coming last. This is enforced at parsing time.

  Multiple groups may be specified, with group names separated by /:

  member = dialin/callback@10.11.12.13
  

  Here, group membership will default to the dialin group. However, appending the separation character * (changeable using the separation tag = character directive), followed by callback to the username at login time will choose the corresponding callback group profile instead.

  To iterate this again: Any user can be a member of exactly one primary group. The dialin/callback syntay in this example actually means: The user is free to choose at login time whether he wants to be a member of dialin XOR callback. User fred may authenticate as fred (or as fred*dialin) to gain dialin membership, and fred*callback will assign him to the callback group.

  The users' choice can be overridden using the tag directive (see below).

  Group membership may depend on NAS IP, e.g. fred could have something like

  member = test1@nas1
  member = test2@nas2
  

  in his profile.

  Just like users, groups can be member of (other) groups:

  group = test1 { ... }
  group = test2 { ... }
                                                                                         
  group = test2 {
     ...
     member = test1
     member = test2@nas1
     ...
  }
  

  Simultaneous membership in (non-hierarchical) groups isn't supported.

  As group membership is resolved when parsing the configuration file, groups and hosts need to be already defined before being used as argument in a member definition.

• tag ( acl [ not ] acl ) = string

  As described above, a user may manually select an (allowed) group profile at login time using the user*group syntax. You can override the user's choice using the tag directive in user or group profiles. Plus, you can make acl-based tag selections. E.g.:

  timespec = workinghours { "* 9-16 * * 1-5" "* 9-12 * * 6" }
  timespec = weekend { "* * * * 6-1" }
  timespec = changewindow { "* 22-23 * * Sat" "* 0-3 * * Sun" }
  
  acl helpdesk = {
      time = workinghours
      nac = internal_lan
      nas = somecustomer
  }
  
  acl remoteadmin = {
      time = changewindow
      nac = dialin
  }
  
  user = fred {
      login = clear test
      member = admin/ro/emergency
      tag acl helpdesk = admin
      tag acl remoteadmin = emergency
      tag = ro
  }
  

  fred will be a member of the admin group during work hours, but only if his client IP address is part of the internal LAN and if he's on a certain NAS. He'll be member of the emergency group during change window hours, but needs to come from the dial-in pool. Outside these hours he's a member of the ro hours.

  tag definitions are evaluated in order. If no definition matches, the user's session tag (the group selected at login time using user*group syntax) is used. If no group tag was given, the first group in the member definition is selected.

  In most cases, it might be a better idea to use member acl syntax instead of tag acl.

• client [ regex ] = ( deny | [ permit ] ) string

  As an alternative (or complement) to ACLs (see above), certain NAC based validity restrictions may be placed in a user (or group) object directly. For example, to limit log-ins to a certain IP range or a host group:

      client = 10.99.0.0/16
      client = deny customer3
  

  If the regex keyword is used, string is expected to be a valid regular expression. Regular expression search is expensive and only used if the NAC address sent by the NAS ist not an IP address. Example for regular expression client matching:

      # if compiled with PCRE:
      client = deny /^async$/
      client regex = /^console$/
  
      # without PCRE:
      client = deny "^async$"
      client regex = "^console$"
  

  	Evaluation Order
  	Please keep in mind that ACLs are checked before client statements. For client definitions, IP addresses are checked before regular expressions, while the latter are evaluated in the order you've defined them.

• server = ( deny | [ permit ] ) string

  This limits user account validity to certain NAS addresses or groups, e.g.:

      server = 1.2.3.4/32
      server = nas01
  

• default service = ( permit | deny )

  This defines whether a service not explicitely defined in the user profile should be permitted or denied.

• prohibit service = service ...

  Use this to override the default service specification. E.g., to explicitely deny the X.25 service:

      prohibit service = x25
  

• enable [ level ] = ( permit | deny | login | ( clear | crypt ) password )

  This directive may be used to set user or group specific enable passwords, to use the login or to permit (without password) or refuse any enable attempt. Enable secrets defined at group or user level have precedence over those defined at host level. level defaults to 15.

  The default privilege level for an ordinary user on the NAS is usually 1. When a user enables, she can reset this level to a value between 0 and 15 by using the NAS enable command. If she doesn't specify a level, the default level she enables to is 15.

---

4.6.1. Railroad Diagrams

---

4.6.2. Service Definitions

Service definitions may appear in user and group sections. Services can easily be made dependent on ACLs:

service ( acl [ not ] ACLName= service { ... }

There are a couple of generic configuration attributes which may appear in arbitrary service definitions. In particular:

• default attribute = ( permit | deny )

  This directive specifies whether the daemon is to accept or reject unknown attributes sent by the NAS (default: deny).

• acl = ( [ permit ] | deny ) [ not ] acl

  Just as user and group profiles, services can be restricted by using ACLs.

• ( set | optional ) attribute = value

  Defines mandatory and optional attribute-value pairs. Example:

  set priv-lvl = 15
  

  For a detailed description on mandatory and optional AV-pairs, see the "The Authorization Algorithm" section somewhere below.

Other configuration attributes are service specific and only valid in certain contexts:

SHELL (EXEC) Service

Shell startup should have an appropriate service

service = shell { }

defined. Valid configuration directive within the curly brackets are:

• default cmd = ( permit | deny )

  This directive specifies whether the daemon is to accept or reject commands not explicitely permitted (default: deny).

• message ( permit | deny ) = string

  This specifies a message to be presented to the user on accepting or rejecting a command. String substitutions within string are %c (command name) and %a (command arguments). Example:

  message permit "Permitted '%c %a'"
  message deny "Denied '%c %a'"
  

  This directive may appear in cmd sections, too, where it overrides the service section definitions.

• cmd = command { ... }

  cmd sections permit or deny commands and command arguments. Example:

  cmd = show {
      deny /^(running|startup)-config/
      deny tech-support
      permit //
      message deny = "Try this again and your account will be revoked."
      message permit = "This data is to be considered confidentional."
  }
  cmd = reload {
      permit //
      message permit = "You hopefully know what you're doing ..."
  }
  

  Regular expression syntax is POSIX or, if enabled at compile time, PCRE.

If you're unsure what commands and arguments the router actually sends for verification, you may simply modify a user (or group) profile to display those within a login session. E.g.,

user = ... {
    ...
    debug = CMD
    ...
    service = shell {
        ...
        message debug  = "author: 'cmd = %c { permit /^%a$/ }"
        ...
    }
}

will display the configuration snippets to permit the command in PCRE syntax:

Router#conf t
author: 'cmd = configure { permit /^terminal <cr>$/ }'

Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#

Non-Shell Services

E.g. for PPP, protocol definitions may be used:

service = ppp {
    protocol = ip { set addr = 1.2.3.4 }
}

Use

    default protocol = permit

or

    default protocol = deny

to specify the default for protocols not explicitly defined within a service declaration. (default: deny).

For a Juniper Networks-specific authorization service, use:

service = junos-exec {
   set local-user-name = NOC
   # see the Junos documentation for more attributes
}

---

4.6.3. Host-group specific services

Services can be configured NAS specific by appending @host to the service name. Here, host is the name of a host object, not an IP address or CIDR range. For example, a user's PPP address could be static on one particular NAS, but dynamic everywhere else:

host = dialin { address = ... }
user = ... {
    service = ppp { protocol = ip { } }
    service = ppp@dialin { protocol = ip { set addr = 1.2.3.4 } }
}

While the same can be achieved using host specific group membership, this adds some flexibility for dynamic authentication backends.

---

4.6.4. CLI Contexts

When used with single-connection and being told so, the daemon tries to remember command context. which permits the shutdown family of commands for exactly one interface, but denies it for all the others:

user = john {
    password = clear doe
    service = shell {
        default cmd = permit
        set priv-lvl = 15
        script = {
            if (cmd =~ /^interface FastEthernet 0\/1 /) {
                message = "Context has been set. \"[no] shut\" should work for you."
                context = FE
                permit
            } else if (cmd =~ /^interface/){
                message = "Context has been reset."
                context = ""
                permit
            }
            if (context == FE) {
                if (cmd =~ /^shutdown/) permit
                if (cmd =~ /^no shutdown/) permit
                deny
            }
        }
        cmd = shutdown { deny . }
        cmd = no { deny /^shutdown/ }
    }       
}

---

4.6.5. Examples

Here we declare two users fred and lily, and two groups, admin and staff.

fred is a member of group admin and group admin is in turn a member of group staff. lily is not a member of any group.

group = admin {
    # group admin is a member of group staff
    member = staff
    service = shell {
        set priv-lvl = 15
    }
}

group = staff {
    # group staff is not a member of any group
}

user = lily {
    # user lily is not a member of any group
    # and has nothing else configured as yet
}

user = fred {
    # fred is a member of group admin on 0.0.0.0/0
    member = admin
    # fred is a member of group staff when logging in on 10.0.0.0/8
    member = staff@10.0.0.0/8
    # fred is a member of group admin when logging in on hosts
    # defined in hostgroup test123
    member = admin@test123
    # fred may only log in from a client in 172.16.0.0/24 ...
    client = 172.16.0.0/24
    # ... or from whatever address is defined in some host object test123
    client = test123
}

---

4.6.6. Railroad Diagrams

---

4.6.7. Configuring Non-local Users via MAVIS

MAVIS configuration is optional. You don't need it if you're content with user configuration in the main configuration file.

A MAVIS configuration file may be specified via

mavis config = file

The MAVIS backend then dynamically creates user entries, based, e.g., on LDAP information. For PAP and LOGIN,

pap backend = mavis
login backend = mavis

in the global section delegate authentiation to the MAVIS sub-system. Statically defined users are still valid, and have a higher precedence.

Relevant MAVIS attributes are

• AV_A_TACCLIENT

  A comma separated list of host object names or IP address ranges in CIDR notation for which the account is valid.

• AV_A_TACMEMBER

  A comma separated list consisting of CIDR-specific group memberships (group@cidr) to set group permissions based on the NAS ip address.

• AV_A_TACPROFILE

  A single line consisting of tac_plus user section configuration directives, e.g.

  { chap = clear "chapsecret" arap = clear "arapsecret" }
  

By default, MAVIS user data will be cached for 120 seconds. You may change that period using

cache timeout = seconds

in the global configuration section.

---

4.6.8. Configuring Local Users for MAVIS authentication

Under certain circumstances you may wish to keep the user definitions in the plain text configuration file, but authenticate against some external system nevertheless, e.g. LDAP or RADIUS. To do so, just specify one of

    login = mavis
    pap = mavis
    password = mavis

in the corresponding user definition.

---

4.6.9. Recursion and Groups

In general, when the daemon looks up values, it will look first to see if the user has her own definition for that value. If not, it looks to see if she belongs to a group and if so, whether the group has a value defined. If not, this process continues through the hierarchy of groups (a group can be a member of another group) until a value is found, or there are no more gmaryroups.

This recursive process occurs for lookups of expiration dates and also for authorization parameters (see later), but not for user passwords.

A typical configuration technique is thus to place users into groups and specify as many groupwide characteristics in the group declaration as possible. Then, individual user declarations can be used to override the group settings for selected users as needed.

---

4.6.10. Configuring User Authentication

User Authentication can be specified separately for PAP, ARAP, CHAP, and normal logins. ARAP, CHAP, and global user authentication must be given in clear text.

The following assigns the user mary five different passwords for ARAP, inbound and outbound CHAP, inbound PAP, outbound PAP, and normal login respectively:

user = mary {
    arap = clear "arap password"
    chap = clear "chap password"
    pap  = clear "inbound pap password"
    opap = clear "outbound pap password"
    login = crypt XQj4892fjk
}

If

user backend = mavis

is configured in the global section, users not found in the configuration file will be looked up by the MAVIS backend. You should consider using this option in conjuction with the more sophisticated backends (LDAP and ActiveDirectory, in particular), or whenever you're not willing to duplicate your pre-existing database user data to the configuration file. For users looked up by the MAVIS backend,

pap backend = mavis

and/or

login backend = mavis

(again, in the global section of the configuration file) will cause PAP and/or Login authentication to be performed by the MAVIS backend (e.g. by performing an LDAP bind), ignoring any corresponding password definitions in the users' profile.

If you just want the users defined in your configuration file to authenticate using the MAVIS backend, simply set the corresponding PAP or Login password field to mavis (there's no need to add the user backend = mavis directive in this case):

user = mary { login = mavis }

---

4.6.11. Configuring Expiry Dates

An entry of the form:

user = lol {
    valid until = YYYY-MM-DD
    login = clear "bite me"
}

will cause the profile to become invalid, starting after the valid until date. Valid date formats are both ISO8601 and the absolute number of seconds since 1970-01-01.

A expiry warning message is sent to the user when she logs in, by default starting at 14 days before the expiration date, but configurable via the warning period directive.

Complementary to profile expiry,

    valid from = YYYY-MM-DD

activates a profile at the given date.

---

4.6.12. Configuring Authentication on the NAS

On the NAS, to configure login authentication, try

aaa new-model
aaa authentication login default group tacacs+ local

(Alternatively, you can try a named authentication list instead of default. Please see the IOS documentation for details.)

Don't lock yourself out.

As soon as you issue this command, you will no longer be able to create new logins to your NAS without a functioning TACACS+ daemon appropriately configured with usernames and password, so make sure you have this ready. As a safety measure while setting up, you should configure an enable secret and make it the last resort authentication method, so if your TACACS+ daemon fails to respond you will be able to use the NAS enable password to login. To do this, configure: aaa authentication login default group tacacs+ enable or, to if you have local accounts: aaa authentication login default group tacacs+ local If all else fails, and you find yourself locked out of the NAS due to a configuration problem, the section on recovering from lost passwords on Cisco's CCO web page will help you dig your way out.

---

4.6.13. Configuring Authorization

Authorization must be configured on both the NAS and the daemon to operate correctly. By default, the NAS will allow everything until you configure it to make authorization requests to the daemon.

On the daemon, the opposite is true: The daemon will, by default, deny authorization of anything that isn't explicitly permitted.

Authorization allows the daemon to deny commands and services outright, or to modify commands and services on a per-user basis. Authorization on the daemon is divided into two separate parts: commands and services.

---

4.6.14. Authorizing Commands

Exec commands are those commands which are typed at a Cisco exec prompt. When authorization is requested by the NAS, the entire command is sent to the tac_plus daemon for authorization.

Command authorization is configured by specifying a list of PCRE (Perl Compatible Regular Expressions) or egrep-style (POSIX 1003.2) case-insensitive regular expressions to match command arguments (see your local pcrematching(3) or regex(7) man page, respectively, for a description of regular expressions), and an action which is deny or permit.

Command authorization is configured by specifying a list of case-insensitive regular expressions to match command arguments, and an action which is deny or permit.

If a POSIX pattern contains spaces or special characters, you'll have to enclose the pattern in double quotes ("). For text inside double quotes, C parsing rules apply. In particular, the backslash \ needs to be escaped as \\. PCRE patterns need to be enclosed in slashes (/pattern/). Both POSIX and PCRE syntax may be used in the same configuration file.

The following configuration example permits user Fred to run the following commands:

telnet 131.108.13.any_number
telnet 128.any_number.12.3
show running-config interface anything 

All other commands are denied (by default).

user=fred {
    # default service = deny
    service = shell { 
        # default cmd = deny
        cmd = telnet {
            # permit specified telnets
            # POSIX:
            permit ^131\.108\.13\.[0-9]+$
            # PCRE:
            permit /^128\.\d+\.12\.3$/
        }
        cmd = show {
            # permit show commands
            # PCRE:
            permit /^running-config interface/
        }
    }
}

	Whitespace
	If any non-PCRE argument list you specify contains spaces or tabs, you must enclose it in double quotes. PCRE expressions are to be enclosed in slashes, anyway.

The command and arguments which the user types gets matched to the regular expressions you specify in the configuration file (in order of appearance). The first successful match performs the associated action (permit or deny). If there is no match, the command is denied by default.

Conversely, the following configuration example can be used to deny the command:

telnet 131.108.13.any_number 

and permit all other arguments, since the last line will match any argument list. All other commands and services are permitted due to the "default service = permit" clause.

Note: the default statement must be the first in the user clause

user=fred {
    default service = permit
    service = shell {
        cmd = telnet {
            # allow all telnet commands except to 131.108.13.*
            deny ^131\.108\.13\.[0-9]+
            permit .*
        }
    }
}

Matches are only anchored if you specify so, so deny 131.108.13.[0-9]+ matches anywhere in the command. To anchor the match, use ^ at the beginning of the regular expression.

When a command has multiple arguments, users may enter them in many different permutations. It can be cumbersome to create regular expressions which will reliably authorize commands under these conditions, so administrators may wish to consider other methods of performing authorization e.g. by configuring NAS-local privileged enable levels on the NAS itself.

---

4.6.14.1. Command Expansion

For command authorization, the Cisco NAS expands all commands to their full names e.g. when you type config t on the NAS, this will be expanded to configuration terminal before being sent to the daemon so that you don't need to list all the possible contractions of a command.

At the user level i.e. inside the braces of a user declaration, the default for a user who doesn't have a service or command explicitly authorized is to deny that service or command. The following directive will permit the service or command by default instead:

user = lol {
    default service = permit
}

Note: This directive must appear first inside the user declaration.

At the service authorization level i.e. inside the braces of a service declaration, arguments in an authorization request are processed according to the algorithm described later. Some actions when authorizing services (e.g. when matching attributes are not found) depend on how the default is configured. The following declaration changes the default from deny to permit for this user and service.

user = lol { service = shell { default attribute = permit } }

Note: This directive must appear before any others inside the service declaration.

Note: for command authorization (as opposed to service authorization being discussed here), you specify deny .* or permit .* as the last line of the regular expression matches to create default behavior.

---

4.6.15. Authorizing EXEC (SHELL) Startup

If you authorize some exec commands, you implicitly agree to allow that user to start an exec (it doesn't make sense to permit exec commands if an exec can't be started to run those commands)

In addition to agreeing to allow an exec to start, you can supply some parameters whenever an exec starts e.g. an autocommand, a dialback string or a connection access list (acl).

In the example below, when an exec is started on the NAS, an acl of 4 will be returned to the NAS:

user=fred {

    # this following line permits an exec to start and permits
    # all commands and services by default

    default service = permit

    service = shell {
        # When an exec is started, its connection access list will be 4.
        # It also has an autocmd.
        set acl = 4
        set autocmd = "telnet foobar"

        cmd = telnet {
            # allow all fred's telnet commands except telnet to 131.108.13.*
            deny 131\.108\.13\.[0-9]+
            permit .*
        }
    }
}

Note: specifying an autocommand, or any other exec services, is part of EXEC AUTHORIZATION. For it to work, you must also configure exec authorization on your NAS e.g.

aaa authorization exec authorlist group tacacs+ local
aaa authorization commands 15 cmdlist group tacacs+ local

and, eventually, on the lines:

authorization commands 15 cmdlist
authorization exec authorlist

Just as with authentication, you can use a named authorization list, or simply default.

---

4.6.16. Authorizing EXEC, SLIP, PPP and ARAP services

Authorizing EXEC, SLIP, PPP and ARAP services is done quite differently from command authorization.

When authorizing these services, the NAS sends a request containing a number of attribute-value (AV) pairs, each having the form

attribute=value

(Note: during debugging, you may see AV pairs whose separator character is a * instead of a = sign, meaning that the value in a pair is optional. An = sign indicates a mandatory value. A * denotes an optional value).

E.g., a user starting PPP/IP using an address of 131.108.12.44 would generate a request with the following AV pairs:

service=ppp
protocol=ip
addr*131.108.12.44

You can use the NAS debugging command

debug aaa authorization

to see what authorization AV pairs are being used by the NAS. Note: If you are not on the router console, you will also need to issue a terminal monitor command to see debug output.

---

4.6.17. The Authorization Process

Authorizing a single session can result in multiple requests being sent to the daemon. For example, in order to authorize a dialin PPP user for IP, the following authorization requests will be made from the NAS:

1. An initial authorization request to startup PPP from the exec, using the AV pairs service=ppp, protocol=ip, will be made (Note: this initial request will be omitted if you are autoselecting PPP, since you won't know the username yet).

   This request is really done to find the address for dumb PPP (or SLIP) clients who can't do address negotiation. Instead, they expect you to tell them what address to use before PPP starts up, via a text message e.g. "Entering PPP. Your address is 1.2.3.4". They rely on parsing this address from the message to know their address.

2. Next, an authorization request is made from the PPP subsystem to see if PPP's LCP layer is authorized. LCP parameters can be set at this time (e.g. callback). This request contains the AV pairs service=ppp, protocol=lcp.

3. Next an authorization request to startup PPP's IPCP layer is made using the AV pairs service=ppp, protocol=ipcp. Any parameters returned by the daemon are cached.

4. Next, during PPP's address negotiation phase, each time the remote peer requests a specific address, if that address isn't in the cache obtained in step 3, a new authorization request is made to see if the peers requested address is allowable. This step can be repeated multiple times until both sides agree on the remote peer's address or until the NAS (or client) decide they're never going to agree and they shut down PPP instead.

---

4.6.18. Authorization Relies on Authentication

Since we pretty much rely on having a username in authorization requests to decide which addresses etc. to hand out, it is important to know where the username for a PPP user comes from. There are generally 2 possible sources:

1. You force the user to authenticate by making her login to the exec and you use that login name in authorization requests. This username isn't propagated to PPP by default. To have this happen, you generally need to configure the if-needed method, e.g.

   aaa authentication login default tacacs+
   aaa authentication ppp default if-needed
   

2. Alternatively, you can run an authentication protocol, PAP or CHAP (CHAP is much preferred), to identify the user. You don't need an explicit login step if you do this (so it's the only possibility if you are using autoselect). This authentication gets done before you see the first LCP authorization request of course. Typically you configure this by doing:

   aaa authentication ppp default tacacs+ 
   int async 1
     ppp authentication chap
   

If you omit either of these authentication schemes, you will start to see authorization requests in which the username is missing.

---

4.6.19. Configuring Service Authorization

A list of AV pairs is placed in the daemon's configuration file in order to authorize services. The daemon compares each NAS AV pair to its configured AV pairs and either allows or denies the service. If the service is allowed, the daemon may add, change or delete AV pairs before returning them to the NAS, thereby restricting what the user is permitted to do.

---

4.6.19.1. The Authorization Algorithm

The complete algorithm by which the daemon processes its configured AV pairs against the list the NAS sends, is given below.

Find the user (or group) entry for this service (and protocol), then for each AV pair sent from the NAS:

1. If the AV pair from the NAS is mandatory:

   1. look for an exact attribute,value match in the user's mandatory list. If found, add the AV pair to the output.

   2. If an exact match doesn't exist, look in the user's optional list for the first attribute match. If found, add the NAS AV pair to the output.

   3. If no attribute match exists, deny the command if the default is to deny, or,

   4. If the default is permit, add the NAS AV pair to the output.

2. If the AV pair from the NAS is optional:

   1. look for an exact attribute,value match in the user's mandatory list. If found, add DAEMON's AV pair to output.

   2. If not found, look for the first attribute match in the user's mandatory list. If found, add DAEMON's AV pair to output.

   3. If no mandatory match exists, look for an exact attribute,value pair match among the daemon's optional AV pairs. If found add the DAEMON's matching AV pair to the output.

   4. If no exact match exists, locate the first attribute match among the daemon's optional AV pairs. If found add the DAEMON's matching AV pair to the output.

   5. If no match is found, delete the AV pair if the default is deny, or

   6. If the default is permit add the NAS AV pair to the output.

3. After all AV pairs have been processed, for each mandatory DAEMON AV pair, if there is no attribute match already in the output list, add the AV pair (but add only ONE AV pair for each mandatory attribute).

---

4.6.19.2. Recursive Authorization

Remember that authorization is also recursive over groups. Thus, if you place a user in a group, the daemon will look in the group for authorization parameters if it cannot find them in the user declaration.

---

4.6.20. Examples

host = 0.0.0.0/0 {
    key = "your key here"
}

group = admin {
    # group members who have no expiry date set will use this one
    valid until = 1997-01-01
    service = shell {
        default cmd = permit
    }
}

user=fred {
    login = crypt mEX027bHtzTlQ
    member = admin
    valid until = 2005-05-23

    service = shell {
        # When Fred starts an exec, his connection access list is 5
        set acl = 5

        # We require this autocmd to be done at startup
        set autocmd = "telnet foo"

        # All commands except show system are denied for Fred
        cmd = show {
            # Fred can run the following show command
            permit system
            deny .
        }
    }

    service = ppp {
        protocol = lcp
        protocol = ip {
            # Fred can run IP over PPP only if he uses one
            # of the following mandatory addresses. If he
            # supplies no address, the first one here will
            # be mandated
            set addr=131.108.12.11
            set addr=131.108.12.12
            set addr=131.108.12.13
            set addr=131.108.12.14

            # Fred's mandatory input access list number is 101
            set inacl=101

            # We will suggest an output access list of 102,
            # but the NAS may choose to ignore or override it
            optional outacl=102
        }
    }

    service = slip {
        default protocol = permit
        # Fred can run SLIP. When he does, he will have to use
        # these mandatory access lists
        set inacl=101
        set outacl=102
    }
}

user = wilma {
    login = crypt mEX027bHtzTlQ
    member = admin
}

---

4.6.21. Configuring Authorization on the NAS

If authorization is not explicitly configured on the NAS, no authorization takes place, i.e. effectively, everything is permitted. Note that this is the converse of what happens on the daemon, where anything not explicitly permitted is denied by default.

To configure command authorization on the NAS, issue the following NAS configuration commands:

aaa authorization commands 15 cmdlist group tacacs+ local

and, on the lines:

aaa authorization commands 1 cmdlist
aaa authorization commands 15 cmdlist

This will make the NAS send TACACS+ requests for all level 1 (ordinary user) and level 15 (privileged level) commands.

Note: As soon as you configure the above on your NAS, you will only be permitted to execute NAS commands which are permitted by your TACACS+ daemon. So make sure you have configured, on the daemon, an authenticated user who is authorized to run commands, or you will be unable to do much on the NAS after turning on authorization.

Alternatively, or in addition, you may also want to configure the following:

aaa authorization commands 1 group tacacs+ if-authenticated

This will use TACACS+ authorization for level 1 (user-level commands) but if problems arise, you can just switch off the TACACS+ server and authorization will then be granted to anyone who is authenticated.

The following daemon configuration should be sufficient to ensure that you can always login as username admin (with a suitable password) and run any command as that user:

user = admin {
    default service = permit
    service = shell { default cmd = permit }
    login = crypt kppPfHq/j6gXs
}

accounting log = /var/log/tac_plus/%Y/%m/%d.access

accounting log = "|exec /usr/bin/logger"

1995-07-13 13:35:28 -0500  172.16.1.4  chein  tty5   171.69.1.141
        stop   task_id=12028  service=exec  port=5   elapsed_time=875
1995-07-13 13:37:04 -0500  172.16.1.4  lol    tty18  171.69.1.129
        stop   task_id=11613  service=exec  port=18  elapsed_time=909
1995-07-13 14:09:02 -0500  172.16.1.4  billw  tty18  171.69.1.152
        start  task_id=17150  service=exec  port=18
1995-07-13 14:09:02 -0500  172.16.1.4  billw  tty18  171.69.1.152
        start  task_id=17150  service=exec  port=18

aaa accounting system default start-stop group tacacs+
aaa accounting exec default start-stop group tacacs+
aaa accounting exec acctlist stop-only group tacacs+
aaa accounting commands 15 acctlist start-stop group tacacs+
aaa accounting network acctlist stop-only group tacacs+

line XX
  accounting commands 15 acctlist

5. MAVIS Configuration

The distribution comes with various MAVIS modules, of which the external module is probably the most interesting, as it interacts with simple Perl scripts to authenticate and authorize requests. You'll find sample scripts in the mavis/perl directory. Have a close look at them, as you may (or will) need to perform some trivial customizations to make them match your local environment.

You should really have a look at the MAVIS documentation. It gives examples for RADIUS and PAM authentication, too.

objectClass: tacacsAccount

dn: uid=marc,ou=people,dc=example,dc=com
uid: marc
cn: Marc Huber
objectClass: posixAccount
objectClass: inetOrgPerson
objectClass: shadowAccount
objectClass: tacacsAccount
shadowMax: 10000
uidNumber: 1000
gecos: Marc Huber
givenName: Marc
sn: Huber
gidNumber: 500
shadowLastChange: 14012
loginShell: /bin/bash
homeDirectory: /Users/marc
mail: marc@example.com
userPassword:: abcdefghijklmnopqrstuvwxyz=
tacacsClient: 192.168.0.0/24
tacacsClient: management
tacacsMember: readonly@172.16.5.0/24
tacacsMember: readwrite@nasgroup
tacacsProfile: { valid until = 2010-01-30 chap = clear ahzoi5Ue }

id = spawnd {
    listen = {
        port = 49
    }
    spawn = {
        instances min = 1
        instances max = 10
    }
    background = yes
}

id = tac_plus {
    access log = /var/log/tacacs/%Y/%m/%d/access.log
    accounting log = /var/log/tacacs/%Y/%m/%d/acct.log

    mavis module = external {
        # Optionally:
        # script out = {
        #     # Require group membership:
        #     if (undef($TACMEMBER) && $RESULT == ACK) set $RESULT = NAK
        #
        #     # Don't cache passwords:
        #     if ($RESULT == ACK) set $PASSWORD_ONESHOT = 1
        # }

        setenv LDAP_SERVER_TYPE = "microsoft"
        # setenv LDAP_HOSTS = "ldaps://ads01:636 ldaps://ads02:636"
        setenv LDAP_HOSTS = "ads01:3268 ads02:3268"
        setenv LDAP_SCOPE = sub
        setenv LDAP_BASE = "dc=example,dc=com"
        setenv LDAP_FILTER = "(&(objectclass=user)(sAMAccountName=%s))";
        setenv LDAP_USER = tacacs@example.com
        setenv LDAP_PASSWD = Secret123
        setenv TACACS_GROUP_PREFIX = tacacs
        # setenv REQUIRE_TACACS_GROUP_PREFIX = 1
        setenv USE_TLS = 0
        exec = /usr/local/lib/mavis/mavis_tacplus_ldap.pl
    }

    login backend = mavis
    pap backend = mavis

    host = world {
        address = ::/0
        prompt = "Welcome\n"
        key = cisco
    }

    host = helpdesklab {
        address = 192.168.34.16/28
    }

    # A user will be in the "admin" group if he's member of the
    # corresponding "tacacsadmin" ADS group.

    group = admin {
        default service = permit
        service = shell {
            default command = permit
            default attribute = permit
            set priv-lvl = 15
        }
    }

    # A user will be in the "helpdesk" group if he's member of the
    # corresponding "tacacshelpdesk" ADS group:

    group = helpdesk {
        default service = permit
        service = shell {
            default command = permit
            default attribute = permit
            set priv-lvl = 1
        }
        enable = deny
        member = admin@helpdesklab
    }
}

mavis module = external {
        exec = /usr/local/lib/mavis_tacplus_radius.pl
        setenv RADIUS_HOST = 1.2.3.4:1812
        setenv RADIUS_SECRET = "mysecret"
        setenv RADIUS_GROUP_ATTR = Some-Radius-Attribute
    }

  { member = Administrator }

    ...
    # set the time interval you want the user to be valid if the backend fails:
    authentication fallback period = 60 # that's actually the default value
    ...
    # add a local user for emergencies:
    user = cisco {
        ...
        fallback-only
        ...
    }

    host = ... {
        ...
        prompt = "Welcome\n"
        prompt fallback = "Welcome\nEmergency accounts are currently enabled.\n"
        ...
    }

    authentication fallback = permit
    host = ... {
        ...
        authentication fallback = deny
        ...
    }

6. Debugging Hints

tac_plus -P config-file 

debug = REGEX

7. Frequently Asked Questions

• Is there a Graphical User Interface of any kind?

  No, unless your favourite text editor does qualify. The configuration syntax is to complex and flexible to be coverable using a GUI. If you're looking for a way to manage your user database then have a look at Webmin, ActiveDirectory, whatever. It's trivial to use those as authentication/authorization backends.

• How do I use the MySQL backend?

  You don't, unless you're willing to write the SQL backend yourself. This isn't hard, really, but obviously depends a lot on your database structure and there's simply no generic enough way to free you from this step. Just have a look at, e.g., the LDAP Perl scripts that come with the distribution. If you're remotely familiar with Perl and your SQL database, then writing the backend will be a piece of cake.

• I'm using the single-connection feature. How can I force my router to close the TCP connections to the TACACS+ server?

  On IOS, show tcp brief will display the TCP connections. Search for the ones terminating at your server, and kill them using clear tcp tcb .... Example:

  Router#sho tcp brief | incl 10.0.0.1.49  
  633BB794  10.0.0.2.17326              10.0.0.1.49                 ESTAB
  6287E4C4  10.0.0.2.24880              10.0.0.1.49                 ESTAB
  Router#clear tcp tcb 633BB794            
  [confirm]
   [OK]
  Router#clear tcp tcb 6287E4C4
  [confirm]
   [OK]
  Router#
  

• Does the daemon require a working DNS?

  No, DNS is not a requirement. You may however use DNS reverse mapping in NAC ACL lists, provided that the software is compiled with lwres support and the corresponding lwresd is running.

• Why do I get PPP authorization failures because of no username in request when I've already logged in and authenticated?

  With aaa authentication ppp default group tacacs+, the ppp authentication overrides the earlier login authentication. If the ppp authentication fails, the username ends up blank. Changing the config to aaa authentication ppp default if-needed group tacacs+ fixes this problem.

• Is there any way to avoid having clear text versions of the ARAP and CHAP secrets in the configuration file?

  CHAP and ARAP require that the server knows the cleartext password (or equivalently, something from which the server can generate the cleartext password). Note that this is part of the definition of CHAP and ARAP, not just the whim of some Cisco engineer who drank too much coffee late one night.

  If we encrypted the CHAP and ARAP passwords in the database, then we'd need to keep a key around so that the server can decrypt them when CHAP or ARAP needs them. So this only ends up being a slight obfuscation and not much more secure than the original scheme.

  In extended TACACS, the CHAP and ARAP secrets were separated from the password file because the password file may be a system password file and hence world readable. But with TACACS+'s native database, there is no such requirement, so we think the best solution is to read-protect the files. Note that this is the same problem that a Kerberos server has. If your security is compromised on the Kerberos server, then your database is wide open. Kerberos does encrypt the database, but if you want your server to automatically restart, then you end up having to "kstash" the key in a file anyway and you're back to the same security problem.

  So storing the cleartext password on the security server is really an absolute requirement of the CHAP and ARAP protocols, not something imposed by TACACS+.

  With the scheme choosen for newer TACACS+ protocol revisions, the NAS sends the challenge information to the TACACS+ daemon and the daemon uses the cleartext password to generate the response and returns that.

  The TACACS+ protocol includes specific protocol knowledge for both ARAP and CHAP. (This version of the daemon implementation no longer supports the SENDPASS mechanism.)

  Note that the above doesn't apply to PAP. You can keep an inbound PAP password DES- or MD5-encrypted, since all you need to do with it is verify that the password the principal gave you is correct.

• How is the typical login authentication sequence done?

  1. NAS sends START packet to daemon

  2. Daemon send GETUSER containing login prompt to NAS

  3. NAS prompts user for username

  4. NAS sends packet to daemon

  5. Daemon sends GETPASS containing password prompt to the NAS

  6. NAS prompts user for password

  7. NAS sends packet to daemon

  8. Daemon sends accept, reject or error to NAS

• What does "default service = permit" really do?

  When a request comes in to authorize exec startup, or ppp (with protocol lcp, ip, ipx), or slip, or arap or a specific command, the daemon looks for a matching declarations for the user (or groups the user is a member of).

  For exec startup, it looks for a service=shell.

  For PPP, it looks for a service=ppp and protocol=one of lcp, ip, ipx.

  For SLIP there must be a service=slip and for ARAP a service=arap clause.

  For commands, there must be a matching cmd=cmdname or a default cmd = permit definition.

  If these aren't found, authorization will fail, unless you say default service = permit.

• How do I make PAP work?

  Avoid using PAP if possible since it's not very secure. If you must use it, PAP passwords may be specified along with ARAP and CHAP passwords for each user.

  For outbound PAP, where you are forced to send a password to the remote host to identify yourself, there is now a separate opap directive e.g.

  opap = clear OOOO
  

  You use this to set the outbound PAP password. It must be a cleartext password.

  	Passwords
  	It is very bad practice to use an outbound PAP password that is the same as any of your inbound passwords. For this reason, a "global" password, defined with the password = clear ... statement, does not apply to outbound PAP, only to inbound PAP, bidirectional CHAP and ARAP.

• How can I deny telneting from a commserver by IP address only i.e. when command is 10.0.1.6 rather than telnet 10.0.1.6?

  The best way to restrict telnet access is by applying an outbound access list via the access class command (or equivalently, via the "acl" avpair). The NAS configuration command

  access-class n out
  

  for example applies a pre-defined standard IP access list (where n is a number from 1 through 99) that governs telnet access from a NAS.

  E.g. the following configuration commands permit outgoing Telnet access from line 1 on the NAS *only* to hosts on network 192.85.55.0:

  access-list 12 permit 192.85.55.0 0.0.0.255
  line 1
    access-class 12 out
  

  Note: You must define the access-list on the NAS. Only then can you use the acl avpair to apply it to a line that a user dials in on.

  Alternatively, you can try configuring transport preferred none on the lines in question. This will force a user to always type telnet 10.0.1.6 in order to telnet out from the NAS. Then you can apply command authorization to this command to restrict it.

• I have an autocommand configured in the NAS-local database and I'm using

  aaa authentication local-override
  

  The autocommand doesn't work, but the username/password does. Why?

  The local-override only applies to the authentication portion of the local database, so if you want an autocommand for this user, you need to also do:

  aaa authorization exec local if-authenticated
  

  This will use the local DB entry if one exists, allow authenticated users otherwise, or fail.

  We don't have a aaa authorization local-override like we do for authentication. Unlike authentication, the local method for authorization is sort of equivalent to a local-override.

• Can TACACS+ only be enabled on a global basis?

  You turn TACACS+ ON on a global basis, but you can then change the behavior of individual lines to whatever you want, e.g.

  aaa authentication login default tacacs+ none
  aaa authentication login oldstyle line
  aaa authentication login none none
  line 1 16
    login authentication default
  line vty 0 4
    login authentication oldstyle
  line 0
    login authentication none
  

  Note that unfortunately, you can't (yet) apply authorization differently to selected lines and interfaces.

• I have leased lines running PPP, and AAA authorization is also configured, so the authorization on the leased lines fails. What should I do?

  Since you can't (yet) configure authorization on a per-line basis, you have to turn on authentication on the leased lines running PPP and configure your TACACS+ server so that it will authorize these lines correctly.

  A more demanding alternative is to modify the TACACS+ server source code to allow any authorizations coming in from the port "SerialXXX" to succeed.

  A third possibility is to not use PPP on those lines, e.g. use HDLC instead. HDLC doesn't require authentication or authorization.

• How many characters may a TACACS+ Username and Password contain?

  The short answer is 31 bytes of username, with up to 254 bytes of password if they are cleartext (8 bytes if passwords are DES encrypted).

  The long answer is that the Cisco NAS allocates a buffer of 1024 bytes, so this is the maximum you can type in, in response to a NAS prompt.

  But the protocol spec allows a username or password length field of just one byte in an authentication packet, so only the first 255 of these characters can be sent to the daemon.

  Now if it's a DES encrypted password, then only the first 8 bytes are significant, per the common unix implementations of crypt.

• How do I limit the number of sessions a user can have?

  With this version of the daemon you can't.

• How can I configure time-outs on an interface via TACACS+?

  Certain per-user/per-interface timeouts may be set by TACACS+ during authorization. As of 11.0, you can set an arap session timeout, and an exec timeout. As of 11.1 you can also set an exec idle timeout.

  There are currently no settable timeouts for PPP or SLIP sessions, but there is a workaround which applies to ASYNC PPP/SLIP idle timeouts started via exec sessions only: This workaround is to set an EXEC (idletime) timeout on an exec session which is later used to start up PPP or SLIP (either via a TACACS+ autocommand or via the user explicitly invoking PPP or SLIP). In this case, the exec idle timeout will correctly terminate an idle PPP or SLIP session. Note that this workaround cannot be used for sessions which autoselect PPP or SLIP.

  An idle timeout terminates a connection when the interface is idle for a given period of time (this is equivalent to the "session-timeout" Cisco IOS configuration directive). The other timeouts are absolute. Of course, any timeouts set by TACACS+ apply only to the current connection.

  user = lol {
      login = clear foobar
         service = shell {
             # disconnect lol if there is no traffic for 5 minutes
             set idletime = 5
             # disconnect lol unconditionally after one hour
             set timeout = 60
      }
  }
  

  You also need to configure exec authorization on the NAS for the above timeouts, e.g.

  aaa authorization exec default group tacacs+
  

  Note that these timeouts only work for async lines, not for ISDN currently.

  Note also that you cannot use the authorization if-authenticated option with these parameters, since that skips authorization if the user has successfully authenticated.

• How do I send VPDN forwarding decisions to an authorization server?

  In 11.2 onwards, VPDN NASs can use TACACS+ to allow an authorization server to make the decision to forward users.

  If VPDN forwarding is turned on, and the username is of the form user@domain, and domain matches a vpdn outgoing configured domain, then an authorization attempt is made for domain (see below).

  When making an authorization call for VPDN, a service type of ppp with a protocol type of vpdn, with a username of domain will be made e.g. when a PPP user comes up on a line with the username foo@bar.com, if vpdn enable and aaa authorization .... is enabled on the box, then a one-time authorization of the name bar.com is attempted.

  If this authorization is successful, no local authentication is attempted on the NAS, and the connection is forwarded via VPDN instead.

  If no VPDN-specific information comes back from this authorization call, the login proceeds as follows:

  If tacacs-server directed-requests are configured (note: this is true by default), then IOS will strip off the domain part of a name of the form user@domain and use "domain" to try and select a TACACS+ server. If successful, the username portion "user", without the domain, will be used for all subsequent authentication, authorization and accounting.

  If directed requests are turned off, then the entire username user@domain is treated as a username.

  vpdn specific information includes the attributes tunnel-id, source-ip (deprecated) and ip-addresses:

  tunnel-id	This AV pair specifies the username that will be used to authenticate the tunnel over which the individual user MID will be projected. This is analogous to the "NAS name" in the "vpdn outgoing" command.
  ip-addresses	This is a list of possible IP addresses that can be used for the end-point of the tunnel. Consult the text at the end of this document for more details on how to configure this attribute.
  source-ip	This is now deprecated. It began in release 11.2(1.4), and was removed in 11.2(4.0.2). This ip address will be used as the source of all VPDN packets generated as part of the VPDN tunnel (see the source-ip keyword in the vpdn outgoing command).

  TACACS+ syntax

  The following syntax is used:

  user = domain {
      service = ppp {
          protocol = vpdn {
              set tunnel-id = name for tunnel authentication
              set ip-addresses = addr [addr ...]
              set source-ip = ip-address
          }
      }
  }
  

  In addition the TACACS+ server can be used to store the usernames for both the NAS (the username specified by "tunnel-id" above) and the Home Gateway. These will be used to authenticate the tunnel.

  Example:

  user = foobar.cisco.com {
      service = ppp {
          protocol = vpdn {
              set tunnel-id = my_nas
              set ip-addresses = "173.20.12.19 173.20.12.20"
              set source-ip = 173.5.10.1
          }
      }
  }
  
  user = my_nas { chap = clear egad }
  
  user = my_home_gateway { chap = clear wowser }
  

  IOS Configuration

  To enable AAA assisted VPDN forwarding on a NAS, the following minimum configuration is required:

  vpdn enable
  aaa new-model
  aaa authorization network default group tacacs+ ...
  

  In addition, if the passwords for the home gateway and NAS are stored on the TACACS+ daemon, the command

  aaa authentication login default group tacacs+ ....
  

  should also be present.

  Beginning with release 11.2(1.4), the additional configuration

  vpdn outgoing cisco.com ip NAS [ source-ip X.X.X.X ]
  

  can be used. This changes in 11.2(4.0.2) and becomes:

  vpdn source-ip X.X.X.X
  vpdn outgoing cisco.com ip NAS
  

• Can someone expand on the use of the optional keyword?

  Most attributes are mandatory i.e. if the daemon sends them to the NAS, the NAS must obey them or deny the authorization. This is the default. It is possible to mark attributes as optional, in which case a NAS which cannot support the attribute is free to simply ignore it without causing the authorization to fail.

  This was intended to be useful in cutover situations where you have multiple NASes running different versions of IOS, some of which support more attributes than others. If you make the new attributes optional, older NASes could ignore the optional attributes while new NASes could apply them. Note that this weakens your security a little, since you are no longer guaranteed that attributes are always applied on successful authorization, so it should be used judiciously.

• Can I do do address pooling on the TACACS+ daemon?

  Not really since nothing on the daemon tracks whether an address is already in use. The best way to manage address pools is to define a non-overlapping pool of addresses on each NAS and return the name of this pool during authorization whenever a user logs in e.g.

  NAS:

  ip local pool foo 1.0.0.1 1.0.0.10
  

  Daemon:

  user = lol { service = ppp { protocol = ip { set addr-pool = foo } } }
  

• What about MSCHAP?

  The daemon contains mschap support. Mschap is configured the same way as chap, only using the mschap keyword in place of the chap keyword.

  Like ARAP, MSCHAP requires DES support. Use the --with-ssl flag when configuring the package.

8. Canned Configurations

Here are some canned configurations for getting demos started:

id = spawnd {
    listen = { port = 49 }
}
id = tac_plus {
    host = any { key = "some key" address = 0.0.0.0/0 }

    # repeat as necessary for each user
    user = fred { login = clear abcdef }
}

aaa new-model
enable secret foobar
! use TACACS+. If server dies, use the enable secret password
aaa authentication login default group tacacs+ enable
tacacs-server host ...
tacacs-server key some key

id = spawnd {
    listen = { port = 49 }
}
id = tac_plus {
    host = any { key = "some key" address = 0.0.0.0/0 }

    # repeat as necessary for each user
    user = fred {
        login = clear abcdef
        service = shell {
            cmd = write  { permit terminal }
            cmd = configure { permit .* }
        }
    }
}

aaa new-model
! all level 15 (privileged commands). If server dies, allow everything
aaa authorization commands 15 default group tacacs+ none
tacacs-server host 10.1.1.1
tacacs-server key some key

id = spawnd {
    listen = { port = 49 }
}
id = tac_plus {
    host = any { key = "some key" address = 0.0.0.0/0 }

    # repeat as necessary for each user
    user = fred {
        login = clear abcdef
        chap = clear lab
        service = ppp { protocol = ip { set addr=1.0.0.2 } }
    }
}

aaa new-model
! authenticate exec logins (if not autoselecting)
aaa authentication login default group tacacs+
! authorize network services via TACACS+
aaa authorization network default group tacacs+
! use TACACS+ for authenticating ppp users
aaa authentication ppp default group tacacs+ 
tacacs-server host 10.1.1.1
tacacs-server key some key
interface Async1
ip address 1.0.0.1 255.0.0.0
async default ip address 172.21.14.55
encapsulation ppp
async dynamic address
async mode interactive
! use chap to authenticate ppp users
ppp authentication chap
line 1
! need "modem inout" here and flow control if using a modem

id = spawnd {
    listen = { port = 49 }
}
id = tac_plus {
    host = any { key = "some key" address = 0.0.0.0/0 }

    user = lol {
        arap = clear arapSecret
        service = arap
    }
}

aaa new-model
aaa authentication arap default group tacacs+
aaa authorization network default group tacacs+
aaa accounting network default start-stop group tacacs+
!
appletalk routing
arap network ...
!
interface Ethernet0
  appletalk cable-range ...
  appletalk zone ...
!
tacacs-server host ...
tacacs-server key ...
!
line 1
  location a modem
  modem answer-timeout 0
  modem InOut
  autoselect arap
  autoselect during-login
  arap enable
  speed ...
  flowcontrol hardware

---

8.5. Callback

	Availability of Callback
	Callback is available only in IOS 11.1 and later, and can only be controlled via TACACS+ for ASYNC lines. ISDN callback can be configured on the NAS but cannot be controlled via AAA.

Here is an example of AAA configuration (with exec and network accounting enabled):

Daemon:

Example of remote TACACS+ server configuration file entry for username foobar:

id = spawnd {
    listen = { port = 49 }
}
id = tac_plus {
    host = any { key = "some key" address = 0.0.0.0/0 }

    user = foobar {
        arap = clear AAAA
        login = clear LLLL
        chap = clear CCCC
        pap = clear PPPP
        opap = clear OOOO
        service = ppp {
            default protocol = permit
            protocol = lcp {
                set callback-dialstring=123456
            }
        }
        service = arap {
            protocol = atalk {
                set callback-dialstring=2345678
            }
        }
        service = shell {
            set callback-dialstring=3456789
            set callback-line=7
            set nocallback-verify=1
        }
    }
}

NAS:

aaa new-model
tacacs-server host XX.XX.XX.XX
tacacs-server key fookey
aaa accounting exec wait-start tacacs+
aaa accounting network wait-start tacacs+

! Example of AAA configuration for Exec:
aaa authentication login execcheck tacacs+
aaa authorization network tacacs+
service exec-callback

line 4
  login authentication execcheck

! Example of AAA configuration for ARAP:
aaa authentication arap arapcheck tacacs+
aaa authorization network tacacs+
arap callback

line 4
  arap authentication arapcheck

! Example of AAA-specific configuration for PPP callback:
aaa new-model
aaa authentication ppp pppcheck tacacs+
aaa authorization network tacacs+

int async 6
  ppp authentication chap pppcheck
  ppp callback accept

9. Authorization AV pairs

The following authorization AV pairs specify which service is being authorized and are typically accompanied by protocol AV pairs and other, additional pairs from the lists below. (For a complete and current list of supported AV pairs and required IOS releases search http://www.cisco.com/ for "TACACS+ Attribute-Value Pairs").

• service=arap

• service=shell

  Used for exec startup, and also for command authorizations.

• service=ppp

• service=slip

• service=system

  Not used

• service=raccess

  Used for managing reverse telnet connections, e.g.:

  user = jim {
  login = clear lab
      service = raccess {
          set port#1 = nasname1/tty2
          set port#2 = nasname2/tty5
      }
  }
  

  Requires IOS configuration:

  aaa authorization reverse-access default group tacacs+ 
  

  See the IOS docs for more details.

• protocol=lcp

  The lower layer of PPP, always brought up before IP, IPX, etc. is brought up.

• protocol=ip

  Used with service=ppp and service=slip to indicate which protocol layer is being authorized.

• protocol=ipx

  Used with service=ppp to indicate which protocol layer is being authorized.

• protocol=atalk

  Used with service=ppp or service=arap.

• protocol=vines

  For VINES over PPP.

• protocol=ccp

  Authorization of CCP (Compression Control Protocol). No other av-pairs associated with this.

• protocol=cdp

  Authorization of CDP (Cisco Discovery Protocol). No other av-pairs associated with this.

• protocol=multilink

  Authorization of multilink PPP. See max-links and load-threshold.

• protocol=unknown

  For undefined/unsupported conditions. Should not occur under normal circumstances.

• cmd (EXEC)

  If the value of cmd is NULL e.g. the AV pair is cmd=, then this is an authorization request for starting an exec (shell). If cmd is non-null, this is a command authorization request, It contains the name of the command being authorized, e.g. cmd=telnet.

• cmd-arg (EXEC)

  During command authorization, the name of the command is given by an accompanying cmd= AV pair, and each command argument is represented by a cmd-arg AV pair e.g. cmd-arg=archie.sura.net Note: cmd-arg should never appear in a configuration file. It is used internally by the daemon to construct a string which is then matched against the regular expressions which appear in a cmd clause in the configuration file.

• acl (ARAP, EXEC)

  For ARAP this contains an access-list number. For EXEC authorization it contains an access-class number, e.g. acl=2. which is applied to the line as the output access class equivalent to the configuration command

  line ...
    access-class 2 out
  

  An outbound access-class is the best way to restrict outgoing telnet connections. Note that a suitable access list (in this case, numbered 2) must be predefined on the NAS.

• inacl (PPP/IP/IPX)

  This AV pair contains an IP or IPX input access list number for slip or PPP e.g. inacl=2. The access list itself must be pre-configured on the Cisco box. Per-user access lists do not work with ISDN interfaces unless you also configure a virtual interface. After 11.2(5.1)F, you can also use the name of a predefined named access list, instead of a number, for the value of this attribute. Note: For IPX, inacl is only valid after 11.2(4)F.

• inacl#n (PPP/IP, PPP/IPX, 11.2(4)F)

  This AV pair contains the definition of an input access list to be installed and applied to an interface for the duration of the current connection, e.g.

  inacl#1="permit ip any any precedence immediate"
  inacl#2="deny igrp 0.0.1.2 255.255.0.0 any"
  

  Attributes are sorted numerically before they are applied. For IP, standard OR extended access list syntax may be used, but it is an error to mix the two within a given access-list. For IPX, only extended access list syntax may be used. See also:

  sho ip access-lists
  sho ip interface
  sho ipx access-lists 
  sho ipx interface
  debug aaa author
  debug aaa per-user
  

• outacl (PPP/IP, PPP/IPX)

  This AV pair contains an IP or IPX output access list number for SLIP. PPP/IP or PPP/IPX connections e.g. outacl=4. The access list itself must be pre-configured on the Cisco box. Per-user access lists do not work with ISDN interfaces unless you also configure a virtual interface. PPP/IPX is supported in 11.1 onwards only. After 11.2(5.1)F, you can also use the name of a predefined named access list, as well as a number, for the value of this attribute.

• outacl#n (PPP/IP, PPP/IPX, 11.2(4)F)

  This AV pair contains an output access list definition to be installed and applied to an interface for the duration of the current connection, e.g.

  outacl#1="permit ip any any precedence immediate"
  outacl#2="deny igrp 0.0.9.10 255.255.0.0 any"
  

  Attributes are sorted numerically before they are applied. For IP, standard OR extended access list syntax may be used, but it is an error to mix the two within a given access-list. For IPX, only extended access list syntax may be used.

  See also:

  sho ip access-lists
  sho ip interface
  sho ipx access-lists 
  sho ipx interface
  debug aaa author
  debug aaa per-user
  

• addr (SLIP, PPP/IP)

  The IP address the remote host should be assigned when a slip or PPP/IP connection is made e.g. addr=1.2.3.4.

• routing (SLIP, PPP/IP)

  Equivalent to the /routing flag in slip and ppp commands. Can have as its value the string true or false.

• timeout (11.0 onwards, ARAP, EXEC)

  Sets the time until an arap or exec session disconnects unconditionally (in minutes), e.g. timeout=60.

• autocmd (EXEC)

  During exec startup, this specifies an autocommand, like the autocommand option to the username configuration command, e.g. autocmd="telnet foo.com".

• noescape (EXEC)

  During exec startup, this specifies "noescape", like the noescape option to the username configuration command. Can have as its value the string true or false, e.g. noescape=true.

• nohangup (EXEC)

  During exec startup, this specifies nohangup, like the nohangup option to the username configuration command. Can have as its value the string true or false, e.g. nohangup=true.

• priv-lvl (EXEC)

  Specifies the current privilege level for command authorizations, a number from zero to 15 e.g. priv-lvl=5. Note: in 10.3 this attribute was priv_lvl i.e. it contained an underscore instead of a hyphen.

• zonelist (ARAP)

  An Appletalk zonelist for arap equivalent to the line configuration command arap zonelist, e.g. zonelist=5.

• addr-pool (11.0 onwards, PPP/IP, SLIP)

  This AV pair specifies the name of a local pool from which to get the IP address of the remote host. Note: addr-pool works in conjunction with local pooling. It specifies the name of a local pool (which needs to be pre-configured on the NAS). Use the ip-local pool command to declare local pools, e.g on the NAS:

  ip address-pool local ip local pool foo 1.0.0.1 1.0.0.10
  ip local pool baz 2.0.0.1 2.0.0.20
  

  Then you can use TACACS+ to return addr-pool=foo or addr-pool=baz to indicate which address pool you want to get this remote node's address from, e.g. on the daemon:

  user = lol { service = ppp { protocol = ip { set addr-pool=foo } }
  

• route (11.1 onwards, PPP/IP, SLIP).

  This AV pair specifies a route to be applied to an interface. During network authorization, the "route" attribute may be used to specify a per-user static route, to be installed via TACACS+. The daemon side declaration is:

  service = ppp {protocol=ip{set route="dst_addr mask [ gateway ]"}}
  

  This indicates a temporary static route that is to be applied. dst_address, mask and gateway are expected to be in the usual dotted-decimal notation, with meanings the same as for the familiar ip route configuration command on a NAS. If gateway is omitted, the peer's address is taken to be the gateway. The route is expunged once the connection terminates.

• route#n (PPP/IP/IPX, 11.2(4)F)

  Same as the route attribute, except that these are valid for IPX as well as IP, and they are numbered, allowing multiple routes to be applied e.g.

  route#1="3.0.0.0 255.0.0.0 1.2.3.4"
  route#2="4.0.0.0 255.0.0.0"
  

  or, for IPX,

  route#1="4C000000 ff000000 30.12.3.4"
  route#2="5C000000 ff000000 30.12.3.5"
  

  See also:

  sho ip route
  sho ipx route
  debug aaa author
  debug aaa per-user
  

• callback-rotary (11.1 onwards, valid for ARAP, EXEC, SLIP or PPP)

  The number of a rotary group (between 0 and 100 inclusive) to use for callback e.g. callback-rotary=34. Not valid for ISDN.

• callback-dialstring (11.1 onwards, valid for ARAP, EXEC, SLIP or PPP)

  sets the telephone number for a callback e.g. callback-dialstring=408-555-1212. Not valid for ISDN.

• callback-line (11.1 onwards, valid for ARAP, EXEC, SLIP or PPP)

  The number of a tty line to use for callback e.g. callback-line=4. Not valid for ISDN.

• nocallback-verify (11.1 onwards, valid for ARAP, EXEC)

  Indicates that no callback verification is required. The only valid value for this parameter is the digit one i.e. nocallback-verify=1. Not valid for ISDN.

• idletime (11.1 onwards, EXEC)

  Sets a value, in minutes, after which an IDLE session will be terminated. Note: Does NOT work for PPP.

• tunnel-id (11.2 onwards, PPP/VPDN)

  This AV pair specifies the username that will be used to authenticate the tunnel over which the individual user MID will be projected. This is analogous to the "NAS name" in the vpdn outgoing command.

• ip-addresses (11.2 onwards, PPP/VPDN)

  This is a space separated list of possible IP addresses that can be used for the end-point of the tunnel. In 11.2(5.4)F, this attribute was extended as follows:

  1. comma (',') is also considered as a delimiter. For example the avpair can now be written as

     ip-addresses = 172.21.9.26,172.21.9.15,172.21.9.4
     

  2. slash ('/') is considered a priority delimiter. When you have a number of Home Gateway routers, it is desirable to consider some as the primary routers and some as backup routers. '/' allow you to config the routers into priority groups, so that the NAS will try to forward the users to the high priority routers, before forwarding to the low priority one.

     For example in the following av-pair:

     ip-addresses = "172.21.9.26 / 172.21.9.15 / 172.21.9.4"
     

     172.21.9.26 is considered to be priority 1,

     172.21.9.15 is considered to be priority 2,

     172.21.9.4 is considered to be priority 3.

     The NAS will try to forward the users to 172.21.9.26, before trying 172.21.9.15. If the NAS can't forward users to 172.21.9.26, it will try 172.21.9.15 next. If it fails with 172.21.9.15, it will then try forwarding to 172.21.9.4.

• source-ip (PPP/VPDN, now deprecated, only existed in releases 11.2(1.4) thru 11.2(4.0.2))

  This specifies a single ip address will be used as the source of all VPDN packets generated as part of the VPDN tunnel (see the equivalent source-ip keyword in the IOS vpdn outgoing command).

• nas-password (PPP/VPDN, 11.2(3.4)F, 11.2(4.0.2)F)

  During L2F tunnel authentication, nas-password specifies the password for the NAS.

• gw-password (PPP/VPDN, 11.2(3.4)F, 11.2(4.0.2)F)

  During L2F tunnel authentication, gw-password specifies the password for the home gateway.

• rte-ftr-in#n (PPP -- IP/IPX, 11.2(4)F)

  This AV pair specifies an input access list definition to be installed and applied to routing updates on the current interface, for the duration of the current connection. For IP, both standard and extended Cisco access list syntax is recognised, but it is an error to mix the two within a given access-list. For IPX, only Cisco extended access list syntax is legal. Attributes are sorted numerically before being applied. For IP, the first attribute must contain the name of a routing process and its identifier (except for rip, where no identifier is needed), e.g.

  rte-fltr-in#0="router igrp 60"
  rte-fltr-in#1="permit 0.0.3.4 255.255.0.0"
  rte-fltr-in#2="deny any"
  

  For IPX, no routing process is needed, e.g.

  rte-fltr-in#1="deny 3C01.0000.0000.0001"
  rte-fltr-in#2="deny 4C01.0000.0000.0002"
  

  See also:

  show ip access-lists
  show ip protocols
  sho ipx access-lists 
  sho ipx interface
  debug aaa author
  debug aaa per-user
  
  router ...
  [no] distribute-list ...
  
  ipx input-network-filter ...
  

• rte-ftr-out#n (PPP/IP, 11.2(4)F)

  This AV pair specifies an input access list definition to be installed and applied to routing updates on the current interface, for the duration of the current connection. For IP, both standard and extended Cisco access list syntax is recognised, but it is an error to mix the two within a given access-list. Attributes are sorted numerically before being applied. The first attribute must contain the name of a routing process and its identifier (except for rip, where no identifier is needed), e.g.

  rte-fltr-out#0="router igrp 60"
  rte-fltr-out#3="permit 0.0.5.6 255.255.0.0"
  rte-fltr-out#4="permit any"
  

  For IPX, no routing process is specified, e.g.

  rte-fltr-out#1="deny 3C01.0000.0000.0001"
  rte-fltr-out#2="deny 4C01.0000.0000.0002"
  

  See also:

  sho ipx access-lists 
  sho ipx interface
  show ip access-lists
  show ip protocols
  debug aaa author
  debug aaa per-user
  
  router ...
    [no] distribute-list ...
  
  ipx output-network-filter ...
  

• sap#n (11.2(4)F PPP/IPX)

  This AV pair specifies static saps to be installed for the duration of a connection e.g.

  sap#1="4 CE1-LAB 1234.0000.0000.0001 451 4"
  sap#2="5 CE3-LAB 2345.0000.0000.0001 452 5"
  

  The syntax of static saps is the same as that used by the IOS ipx sap command.

  See also:

  sho ipx servers
  debug aaa author
  debug aaa per-user
  [no] ipx sap ...
  

• route#n (PPP/IP/IPX, 11.2(4)F)

  Same as the route attribute, except that these are valid for IPX as well as IP, and they are numbered, allowing multiple routes to be applied e.g.

  route#1="3.0.0.0 255.0.0.0 1.2.3.4"
  route#2="4.0.0.0 255.0.0.0"
  

  or, for IPX,

  route#1="4C000000 ff000000 30.12.3.4"
  route#2="5C000000 ff000000 30.12.3.5"
  

  See also:

  sho ip route
  sho ipx route
  debug aaa author
  debug aaa per-user
  

• sap-fltr-in#n (PPP/IPX, 11.2(4)F)

  This AV pair specifies an input sap filter access list definition to be installed and applied on the current interface, for the duration of the current connection. Only Cisco extended access list syntax is legal, e.g

  sap-fltr-in#1="deny 6C01.0000.0000.0001"
  sap-fltr-in#2="permit -1"
  

  Attributes are sorted numerically before being applied.

  See also:

  sho ipx access-lists 
  sho ipx interface
  debug aaa author
  debug aaa per-user
  ipx input-sap-filter ...
  

• sap-fltr-out#n (PPP/IPX 11.2(4)F)

  This AV pair specifies an output sap filter access list definition to be installed and applied on the current interface, for the duration of the current connection. Only Cisco extended access list syntax is legal, e.g

  sap-fltr-out#1="deny 6C01.0000.0000.0001"
  sap-fltr-out#2="permit -1"
  

  Attributes are sorted numerically before being applied.

  See also:

  sho ipx access-lists 
  sho ipx interface
  debug aaa author
  debug aaa per-user
  ipx output-sap-filter ...
  

• pool-def#n (PPP/IP, 11.2(4)F)

  This attribute is used to define ip address pools on the NAS. During IPCP address negotiation, if an ip pool name is specified for a user (see the addr-pool attribute), a check is made to see if the named pool is defined on the NAS. If it is, the pool is consulted for an ip address. If the required pool is not present on the NAS (either in the local config, or as a result of a previous download operation), then an authorization call to obtain it is attempted, using the special username:

  nas-name-pools
  

  where nas-name is the configured name of the NAS. Note: This username can be changed using the IOS configuration directive e.g.

  aaa configuration config-name nas1-pools-definition.cisco.us
  

  The pool-def attribute is used to define ip address pools for the above authorization call e.g.

  user = foo {
      login = clear lab
      service = ppp { protocol = ip { set addr-pool=bbb } }
  }
  
  user = nas1-pools {
      service = ppp {
          protocol = ip {
              set pool-def#1 = "aaa 1.0.0.1 1.0.0.3"
                  set pool-def#2 = "bbb 2.0.0.1 2.0.0.10"
                  set pool-def#3 = "ccc 3.0.0.1 3.0.0.20"
                  set pool-timeout = 60
          }
      }
  }
  

  In the example above is a configuration file fragment for defining 3 pools named aaa, bbb and ccc on the NAS named nas1. When the user foo refers to the pool named bbb, if the pool bbb isn't defined, the NAS will attempt to download the definition contained in the nas1-pools entry. The other pools will also be defined at the same time (or they will be ignored if they are already defined). Since this procedure is only activated when an undefined pool is referenced, one way to redefine a pool once it has been downloaded is to manually delete the definition e.g. by logging into the NAS, enabling, and configuring:

  config t
  no ip local pool bbb
  ^Z
  

  When a pool is deleted, there is no interruption in service for any user who is currently using a pool address. If a pool is deleted and then subsequently redefined to include a pool address that was previously allocated, the new pool will pick up the allocated address and track it as expected. Since downloaded pools do not appear in the NAS configuration, any downloaded pool definitions automatically disappear whenever a NAS reboots. These pools are marked as "dynamic" when they appear in the output of the show ip local pools NAS command. Since it is desirable not to have to manually delete pools to redefine them, the AV pair pool-timeout=n can be used to timeout any downloaded pool definitions. The timeout n is in minutes. The effect of the pool-timeout attribute is to start a timer when the pool definitions are downloaded. When the timer expires, the pools are deleted. The next reference to a deleted pool via will cause a re-fetch of the pool definitions. This allows pool changes to be made on the daemon and propagated to the NAS in a timely manner. See also:

  sho ip local pool ...
  ip local pool ...
  

• old-prompts (PPP/SLIP)

  This attribute allows providers to make the prompts in TACACS+ appear identical to those of earlier systems (TACACS and XTACACS). This will allow administrators to upgrade from TACACS/XTACACS to TACACS+ transparently to users. The difference between the prompts is as follows: In XTACACS, when the user types slip or ppp the system prompts for an address followed by a password, whereas TACACS+ prompts only for an address. In XTACACS, if the user types slip host or ppp host, the system prompts for a password. In TACACS+, there is no prompt. Using this attribute, TACACS+ can be made to mimic the prompting behaviour of xtacacs, by configuring network authorization on IOS, and using the old-prompts=true attribute value pair for slip and ppp/ip, viz:

  user = joe {
      service = shell { }
      service = slip {
          default attribute = permit
          set old-prompts=true
      }
      service = ppp {
          protocol = ip {
              default attribute = permit
              set old-prompts=true
          }
      }
  }
  

  i.e. the prompts are controlled by the addition of the old-prompts=true attribute.

• max-links (PPP/multilink - Multilink parameter; 11.3)

  This AV pair restricts the number of multilink bundle links that a user can have. The daemon side declaration is:

  service=ppp { protocol=multilink { set max-links=n } }
  

  The range of n is [1-255].

  Related NAS commands:

  int foo
    [no] ppp multilink
  
  int virtual-template X
    multilink max-links n
  show ppp multilink
  debug multilink
  

• load-threshold (PPP/multilink - Multilink parameter; 11.3)

  This AV pair sets the load threshold at which an additional multilink link is added to the bundle (if load goes above) or deleted (if load goes below). The daemon side declaration is:

  service=ppp { protocol=multilink { set load-threshold=n } }
  

  The range of n is [1-255]. Related NAS commands:

  int foo
   [no] ppp multilink
  
  int virtual-template X
    multilink load-threshold n
  
  show ppp multilink
  
  debug multilink
  

• ppp-vj-slot-compression

  Reserved for future use.

• link-compression

  Reserved for future use.

• asyncmap

  Reserved for future use.

• x25-addresses (PPP/VPDN)

  Reserved for future use.

• frame-relay (PPP/VPDN)

  Reserved for future use.

10. Upgrading from Previous Releases

There may be some caveats to consider if you're using a previous version of the software:

• 16-08-2009: To use the MAVIS backend for users not defined in the local configuration file, user backend = mavis is now required.

• 13-06-2010: LDAP functionality was merged into a single script, requiring the environmental variable LDAP_SERVER_TYPE to be set to generic if you were using the mavis_tacplus_ldap_authonly.pl script, to tacplus_schema for functionality equivalent to mavis_tacplus_ldap.pl, and to microsoft for mavis_tacplus_ads.pl functionality.

11. Bugs

• There may still be some nasty bugs lurking in the code. Please contact the author if you think you've found one.

• This documentation isn't well structured.

• The examples given are too IPv4-centric. However, the daemon handles IPv6 just fine.

• Some of the NAS configuration examples aren't recently tested. Refer to the IOS documentation for IOS configuration syntax guidance.

12. References

• draft-grant-tacacs-02.txt ‐ The TACACS+ Protocol (Version 1.78)

• ftp://ftp-eng.cisco.com/pub/tacacs/

13. Copyrights and Acknowledgements

Please see the source for copyright and licensing information of individual files.

• Railroad Diagrams

  The Railroad Diagrams in this documentation were created using ANTLRWorks (http://www.antlr.org/works/).

• The following applies if the software was compiled with OpenSSL support:

  This product includes software developed by the OpenSSL Project for use in the OpenSSL Toolkit (http://www.openssl.org/).

  This product includes cryptographic software written by Eric Young (<eay@cryptsoft.com>).

• MD4 algorithm:

  The software uses the RSA Data Security, Inc. MD4 Message-Digest Algorithm.

• MD5 algorithm:

  The software uses the RSA Data Security, Inc. MD5 Message-Digest Algorithm.

• If the software was compiled with PCRE (Perl Compatible Regular Expressions) support, the following applies:

  Regular expression support is provided by the PCRE library package, which is open source software, written by Philip Hazel, and copyright by the University of Cambridge, England. (ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/).

• The original tac_plus code (which this software and considerable parts of the documentation are based on) is distributed under the following license:

  Copyright (c) 1995-1998 by Cisco systems, Inc.

  Permission to use, copy, modify, and distribute this software for any purpose and without fee is hereby granted, provided that this copyright and permission notice appear on all copies of the software and supporting documentation, the name of Cisco Systems, Inc. not be used in advertising or publicity pertaining to distribution of the program without specific prior permission, and notice be given in supporting documentation that modification, copying and distribution is by permission of Cisco Systems, Inc.

  Cisco Systems, Inc. makes no representations about the suitability of this software for any purpose. THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.

• The code written by Marc Huber is distributed under the following license:

  Copyright (C) 1999-2010 Marc Huber (<Marc.Huber@web.de>). All rights reserved.

  Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

  1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

  2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

  3. The end-user documentation included with the redistribution, if any, must include the following acknowledgment:

     This product includes software developed by Marc Huber (<Marc.Huber@web.de>).

     Alternately, this acknowledgment may appear in the software itself, if and wherever such third-party acknowledgments normally appear.

  THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL ITS AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.