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

Cisco IOS Release: Multiple releases (see the Feature History table)

router bgp as-number

neighbor ip-address remote-as as-number

neighbor ip-address local-as [as-number [no-prepend [replace-as [dual-as]]]

neighbor ip-address remove-private-as

end

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

•

Enter your password if prompted.

Step 2

configure

terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

router bgp

as-number

Example:

Router(config)# router bgp 100

Enters router configuration mode, and creates a BGP
routing process.

Step 4

neighbor

ip-address remote-as as-number

Example:

Router(config-router)# neighbor 10.0.0.1

remote-as 200

Establishes a peering session with a BGP neighbor.

Step 5

neighbor

ip-address local-as [as-number

[no-prepend [replace-as [dual-as]]]]

Example:

Router(config-router)# neighbor 10.0.0.1

local-as 300 no-prepend replace-as dual-as

Customizes the AS_PATH attribute for routes received from
an eBGP neighbor.

•

The replace-as keyword is used to prepend only the
local autonomous-system number (as configured with
the ip-address argument) to the AS_PATH attribute.
The autonomous-system number from the local BGP
routing process is not prepended.

•

The dual-as keyword is used to configure the eBGP
neighbor to establish a peering session using the real
autonomous-system number (from the local BGP
routing process) or by using the autonomous-system
number configured with the ip-address argument
(local-as).

•

The example configures the peering session with the
10.0.0.1 neighbor to accept the real autonomous system
number and the local-as number.