Cisco Cisco IOS Software Release 12.2(27)SBC
BGP Support for Dual AS Configuration for Network AS Migrations
How to Configure Autonomous System Migration
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Cisco IOS Release: Multiple releases (see the Feature History table)
How to Configure Autonomous System Migration
This section contains the following procedures:
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Configuring Dual-AS Peering for Network Migration
The neighbor local-as command is used to customize the AS_PATH attribute by adding and removing
autonomous system numbers for routes received from eBGP neighbors. This feature allows a router to
appear to external peers as a member of another autonomous system for the purpose of autonomous
system number migration. This feature simplifies this process of changing the autonomous-system
number in a BGP network by allowing the network operator to merge a secondary autonomous system
into a primary autonomous system and then later update the customer configurations during normal
service windows without disrupting existing peering arrangements.
autonomous system numbers for routes received from eBGP neighbors. This feature allows a router to
appear to external peers as a member of another autonomous system for the purpose of autonomous
system number migration. This feature simplifies this process of changing the autonomous-system
number in a BGP network by allowing the network operator to merge a secondary autonomous system
into a primary autonomous system and then later update the customer configurations during normal
service windows without disrupting existing peering arrangements.
Confederations, Individual Peering Sessions and Peer Groupings are Supported
This feature supports confederations, individual peering sessions and configurations applied through
peer-groups and peer templates. If this feature is applied to a group peers, the individual peers cannot be
customized.
peer-groups and peer templates. If this feature is applied to a group peers, the individual peers cannot be
customized.
Ingress Filtering can be Applied to Minimize the Possibility of Routing Loop Creation
Autonomous-system path customization increases the possibility that routing loops can be created if
misconfigured. The larger the number of customer peerings, the greater the risk. You can minimize this
possibility by applying policies on the ingress interfaces to block the autonomous-system number that
is in transition or routes that have no local-as configuration.
misconfigured. The larger the number of customer peerings, the greater the risk. You can minimize this
possibility by applying policies on the ingress interfaces to block the autonomous-system number that
is in transition or routes that have no local-as configuration.
Caution
BGP prepends the autonomous system number from each BGP network that a route traverses to maintain
network reachability information and to prevent routing loops. This feature should be configured only
for autonomous-system migration, and should be deconfigured after the transition has been completed.
This procedure should be attempted only by an experienced network operator, as routing loops can be
created with improper configuration.
network reachability information and to prevent routing loops. This feature should be configured only
for autonomous-system migration, and should be deconfigured after the transition has been completed.
This procedure should be attempted only by an experienced network operator, as routing loops can be
created with improper configuration.
Restrictions
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This feature can be configured for only true eBGP peering sessions. This feature cannot be
configured for two peers in different subautonomous systems of a confederation.
configured for two peers in different subautonomous systems of a confederation.
•
This feature can be configured for individual peering sessions and configurations applied through
peer-groups and peer templates. If this command is applied to a group of peers, the peers cannot be
individually customized.
peer-groups and peer templates. If this command is applied to a group of peers, the peers cannot be
individually customized.
SUMMARY STEPS
1.
enable
2.
configure terminal