Cisco Cisco IOS Software Release 12.2(14)S
BGP Hide Local-Autonomous System
How to Configure BGP Hide Local-Autonomous System
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Cisco IOS Release 12.0(18)S, 12.2(8)T, and 12.2(14)S
feature can be used to help transparently change the autonomous system number of a BGP network and
ensure that routes are propagated throughout the autonomous system, while the autonomous system
number transition is incomplete. Because the local autonomous system number is not prepended to these
routes, external routes will not be rejected by internal peers during the transition from one autonomous
system number to another.
ensure that routes are propagated throughout the autonomous system, while the autonomous system
number transition is incomplete. Because the local autonomous system number is not prepended to these
routes, external routes will not be rejected by internal peers during the transition from one autonomous
system number to another.
Caution
BGP prepends the autonomous system number from each BGP network that a route traverses. This
behavior is designed to maintain network reachability information and to prevent routing loops from
occurring. Configuring this feature incorrectly could create routing loops. So, the configuration of this
feature should only be attempted by an experienced network operator.
behavior is designed to maintain network reachability information and to prevent routing loops from
occurring. Configuring this feature incorrectly could create routing loops. So, the configuration of this
feature should only be attempted by an experienced network operator.
Benefits of the BGP Hide Local-Autonomous System Feature
You can use the BGP Hide Local-Autonomous System feature to transparently change the autonomous
system number of a BGP network and ensure that routes can be propagated throughout the autonomous
system while the autonomous system number transition is incomplete.
system number of a BGP network and ensure that routes can be propagated throughout the autonomous
system while the autonomous system number transition is incomplete.
How to Configure BGP Hide Local-Autonomous System
This section contains the following procedures:
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Configuring BGP to Not Prepend the Local Autonomous System Number to
Routes Learned From External Peers
Routes Learned From External Peers
To configure a router that is running BGP with the BGP Hide Local-Autonomous System feature to not
prepend the local autonomous system number to routes that are received from external peers, use the
following steps.
prepend the local autonomous system number to routes that are received from external peers, use the
following steps.
Configuring the no-prepend Keyword
The no-prepend keyword should be used only to change the autonomous system number in a BGP
network and should be deconfigured after the transition is complete because routing loops can be created
if this feature is used incorrectly.
network and should be deconfigured after the transition is complete because routing loops can be created
if this feature is used incorrectly.
Caution
BGP prepends the autonomous system number from each BGP network that a route traverses. This
behavior is designed to maintain network reachability information and to prevent routing loops from
occurring. Configuring this feature incorrectly could create routing loops. So, the configuration of this
feature should only be attempted by an experienced network operator.
behavior is designed to maintain network reachability information and to prevent routing loops from
occurring. Configuring this feature incorrectly could create routing loops. So, the configuration of this
feature should only be attempted by an experienced network operator.