Administrator Guide

Layer 3 Routing Commands 1427
set as-path
To prepend one or more AS numbers to the AS path in a BGP route, use the
set as-path command. To remove a set command from a route map, use the
no form of this command.
Syntax
set as-path prepend as-path-string
no set as-path prepend as-path-string
• prepend as-path-string — A list of AS path numbers to insert at the
beginning of the AS_PATH attribute of matching BGP routes. To prepend
more than one AS number, separate the ASNs with a space and enclose the
string in quotes. Up to ten AS numbers may be prepended.
Default Configuration
No AS paths are prepending by default.
Command Mode
Route Configuration
User Guidelines
This command is normally used to insert one or more instances of the local
AS number at the beginning of the AS_PATH attribute of a BGP route.
Doing so increases the AS path length of the route. The AS path length has a
strong influence on BGP route selection. Changing the AS path length can
influence route selection on the local router or on routers to which the route
is advertised.
When prepending an inbound route, if the first segment in the AS_PATH of
the received route is an AS_SEQUENCE,
as-path-string is inserted at the
beginning of the sequence. If the first segment is an AS_SET,
as-path-string is
added as a new segment with type AS_SEQUENCE at the beginning of the
AS path. When prepending an outbound route to an external peer,
as-path-
string
follows the local AS number, which is always the first ASN.
Command History
Introduced in version 6.2.0.1 firmware.
2CSNXXX_SWUM204.book Page 1427 Monday, January 25, 2016 1:25 PM