Setup Two AS number on NE20

Hi @mrod,

You can use the "peer fake-as" command.

Function
The peer fake-as command configures the local device to use a fake AS number to set up a BGP peer relationship with the specified peer.

The undo peer fake-as command cancels the existing configuration.

By default, a peer uses the actual local AS number.

Format
peer { group-name | ipv4-address | ipv6-address } fake-as { as-number-plain | as-number-dot } [ dual-as ] [ prepend-global-as ] [ prepend-fake-as ]

Usage Guidelines
Usage Scenario

The peer fake-as command is used in a scenario where a carrier modifies network deployment. For example, in a carrier merger and acquisition scenario, if the acquirer's network and the acquiree's network belong to different ASs, BGP peers on the acquiree's network need to be shifted from their original AS to the AS of the acquirer's AS. If the customers of the acquiree do not want their BGP configurations to be changed or do not want them to be changed immediately during the shift, BGP peer relationships may be interrupted for a long time.

In Figure 1, the AS number of carrier A is 100, whereas the AS number of carrier B is 200. Device A belongs to carrier B. Then carrier A acquires carrier B. In this case, the AS number of device A needs to be changed from 200 to 100. Because device A already has a BGP peer relationship established with device B in AS 300 using AS 200, device A's AS number used to establish the BGP peer relationship needs to be changed to 100. The carrier of AS 100 and the carrier of AS 300 then need to communicate about the change. In addition, the AS number configured on device A and peer AS number configured on device B may not be changed at the same time, which will lead to a lengthy interruption of the BGP peer relationship between the two devices. To ensure a smooth merger, you can run the peer fake-as command on device A to set AS 200 of carrier B as a fake AS number so that device A's AS number used to establish the BGP peer relationship between devices A and B does not need to be changed.

In addition, the AS number of the original BGP speakers of carrier B may be changed to the actual AS number at any time when BGP peer relationships are established with devices of carrier A after the merger. If carrier B has a large number of BGP speakers and some of the speakers use the actual AS number whereas other speakers use the fake AS number during BGP peer relationship establishment with devices of carrier A, the local configuration on BGP speakers of carrier B needs to be changed based on the configuration of the peer AS number, which increases the workload of maintenance. To address this problem, you can run the peer fake-as command with dual-as specified to allow the local end to use the actual or fake AS number to establish a BGP peer relationship with the specified peer.

Example
# Set a 2-byte fake AS number for a peer.

<HUAWEI> system-view
[~HUAWEI] bgp 100
[*HUAWEI-bgp] peer 1.1.1.2 as-number 200
[*HUAWEI-bgp] peer 1.1.1.2 fake-as 99
# Set a 4-byte fake AS number for a peer.

<HUAWEI> system-view
[~HUAWEI] bgp 100
[*HUAWEI-bgp] peer 1.1.1.2 as-number 200
[*HUAWEI-bgp] peer 1.1.1.2 fake-as 100.200