Brocade FastIron Ethernet Switch Layer 3 Routing Configuration Guide - Manual (Page 437)

Filtering
This section describes the following:
• AS-path filtering
• Route-map continue clauses for BGP4 routes
• Defining and applying IP prefix lists
• Defining neighbor distribute lists
• Defining route maps
• Router-map continue clauses for BGP4 routes
• Configuring cooperative BGP4 route filtering
AS-path filtering
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 filters
• 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.
device(config)# ip as-path access-list acl1 permit 100
device(config)# router bgp
device(config-bgp-router)# neighbor 10.10.10.1 filter-list acl1 in
Syntax: [no] ip as-path access-list string [ seq s eq-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 seqseq-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.
Filtering
FastIron Ethernet Switch Layer 3 Routing Configuration Guide 437
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