Filtering Communities - Dell PowerConnect B-RX Configuration Manual

26
Filtering

Filtering communities

You can filter routes received from BGP4 neighbors based on community names.
A community is an optional attribute that identifies the route as a member of a user-defined class
of routes. Community names are arbitrary values made of two five-digit integers joined by a colon.
You determine what the name means when you create the community name as one of a route's
attributes. Each string in the community name can be a number from 0 – 65535.
This format allows you to easily classify community names. For example, a common convention
used in community naming is to configure the first string as the local AS and the second string as
the unique community within that AS. Using this convention, communities 1:10, 1:20, and 1:30
can be easily identified as member communities of AS 1.
The BigIron RX provides the following methods for filtering on community information:
•
•
NOTE
The BigIron RX cannot actively support community filters and community list ACLs at the same time.
Use one method or the other but do not mix methods.
NOTE
Once you define a filter or ACL, the default action for communities that do not match a filter or ACL
is "deny". To change the default action to "permit", configure the last filter or ACL entry as "permit
any any".
Community filters or ACLs can be referred to by match statements in a route map.
Defining a community ACL
To configure community ACL 1, enter a command such as the following.
BigIron RX(config)# ip community-list 1 permit 123:2
This command configures a community ACL that permits routes that contain community 123:2.
NOTE
Refer to
community list as a match condition in a route map.
Syntax: ip community-list standard <string> [seq <seq-value>] deny | permit <community-num>
Syntax: ip community-list extended <string> [seq <seq-value>] deny | permit
The <string> parameter specifies the ACL name. (If you enter a number, the CLI interprets the
number as a text string.)
The standard or extended parameter specifies whether you are configuring a standard community
ACL or an extended one. A standard community ACL does not support regular expressions whereas
an extended one does. This is the only difference between standard and extended IP community
lists.
788
Community filters - refer to
Community list ACLs
"Matching based on community ACL"
<community-num> | <regular-expression>
"Defining a community filter"
on page 794 for information about how to use a
on page 744.
BigIron RX Series Configuration Guide
53-1001986-01