Filtering On An As-Path Attribute - Dell S4048T Configuration Manual

• Local router supports graceful restart for this neighbor or peer-group as a receiver only.
CONFIG-ROUTER-BGP mode
neighbor {ip-address | peer-group-name} graceful-restart [role receiver-only]
• Set the maximum time to retain the restarting neighbor's or peer-group's stale paths.
CONFIG-ROUTER-BGP mode
neighbor {ip-address | peer-group-name} graceful-restart [stale-path-time time-
in-seconds]
The default is 360 seconds.

Filtering on an AS-Path Attribute

You can use the BGP attribute, AS_PATH, to manipulate routing policies.
The AS_PATH attribute contains a sequence of AS numbers representing the route's path. As the route
traverses an AS, the ASN is prepended to the route. You can manipulate routes based on their AS_PATH to
affect interdomain routing. By identifying certain ASN in the AS_PATH, you can permit or deny routes based
on the number in its AS_PATH.
AS-PATH ACLs use regular expressions to search AS_PATH values. AS-PATH ACLs have an "implicit deny."
This means that routes that do not meet a deny or match filter are dropped.
To configure an AS-PATH ACL to filter a specific AS_PATH value, use these commands in the following
sequence.
1 Assign a name to a AS-PATH ACL and enter AS-PATH ACL mode.
CONFIGURATION mode
ip as-path access-list as-path-name
2 Enter the parameter to match BGP AS-PATH for filtering.
CONFIG-AS-PATH mode
{deny | permit} filter parameter
This is the filter that is used to match the AS-path. The entries can be any format, letters, numbers, or
regular expressions.
You can enter this command multiple times if multiple filters are desired.
For accepted expressions, refer to
3 Return to CONFIGURATION mode.
AS-PATH ACL mode
exit
4 Enter ROUTER BGP mode.
CONFIGURATION mode
router bgp as-number
5 Use a configured AS-PATH ACL for route filtering and manipulation.
Regular Expressions as
Border Gateway Protocol IPv4 (BGPv4)
Filters.
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