How Communities Are Evaluated

The policy framework software evaluates communities as follows:

• Each route is evaluated against each named community in a routing policy from statement. If a route matches one of the named communities in the from statement, the evaluation of the current term continues. If a route does not match, the evaluation of the current term ends.
• The route is evaluated against each member of a named community. The evaluation of all members must be successful for the named community evaluation to be successful.
• Each member in a named community is either a literal community value or a regular expression. Each member is evaluated against each community associated with the route. (Communities are an unordered property of a route. For example, 1:2 3:4 is the same as 3:4 1:2.) Only one community from the route is required to match for the member evaluation to be successful.
• Community regular expressions are evaluated on a character-by-character basis. For example, if a route contains community 1234:5678, the regular expressions see nine discrete characters, including the colon (:), instead of two sets of numbers (1234 and 5678) separated by a colon. For example:

  [edit]

  policy-options {

  policy-statement one {

  from {

  community [comm-one comm-two];

  }

  }

  community comm-one members [ 1:2 "^4:(5|6)$" ];

  community comm-two members [ 7:8 9:10 ];

  }

  Note: If a community member is a regular expression, a string match is made rather than a numeric match.

• To match routing policy one, the route must match either comm-one or comm-two.
• To match comm-one, the route must have a community that matches 1:2 and a community that matches 4:5 or 4:6.
• To match comm-two, the route must have a community that matches 7:8 and a community that matches 9:10.

Copyright © 2009, Juniper Networks, Inc. All rights reserved. Trademark Notice.