Filtering, Filtering as-paths, Defining an as-path acl – Brocade Multi-Service IronWare Routing Configuration Guide (Supporting R05.6.00) User Manual
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Multi-Service IronWare Routing Configuration Guide
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Filtering
Filtering
This section describes how to configure filters for AS-paths, communities, and other BGP4
attributes.
Filtering AS-paths
You can filter updates received from BGP4 neighbors based on the contents of the AS-path list
accompanying the updates. For example, to deny routes that have the AS 10.3.2.1 in the AS-path
from entering the BGP4 route table, you can define a filter.
The device provides the following methods for filtering on AS-path information:
•
•
AS-path ACLs
NOTE
The device cannot support AS-path filters and AS-path 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 updates that do not match a filter is deny. To
change the default action to permit, configure the last filter or ACL as permit any any.
AS-path filters or AS-path ACLs can be referred to by the filter list number of a BGP4 neighbor as
well as by match clauses in a route map.
Defining an AS-path ACL
To configure an AS-path list that uses “acl 1”, enter a command such as the following.
Brocade(config)# ip as-path access-list acl1 permit 100
Brocade(config)# router bgp
Brocade(config-bgp)# neighbor 10.10.10.1 filter-list acl1 in
Syntax: [no] ip as-path access-list string [seq seq-value] deny | permit regular-expression
The ip as-path command configures an AS-path ACL that permits routes containing AS number 100
in their AS paths. The neighbor command then applies the AS-path ACL to advertisements and
updates received from neighbor 10.10.10.1. In this example, the only routes the device permits
from neighbor 10.10.10.1 are those whose AS-paths contain AS-path number 100.
The string parameter specifies the ACL name. (If you enter a number, the CLI interprets the number
as a text string.)
The seq seq-value parameter is optional and specifies the sequence number for the AS-path list. If
you do not specify a sequence number, the software numbers in increments of 5, beginning with
number 5. The software interprets the entries in an AS-path list in numerical order, beginning with
the lowest sequence number.
The deny | permit parameter specifies the action the software takes if the AS-path list for a route
matches a match clause in this ACL. To configure the AS-path match clauses in a route map, use
the match as-path command. Refer to