How to configure a BGP peer to set up connections with a local end using a fake AS number on S series switches

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For S series switches that support BGP, the peer fake-as command configures the specified peer to establish a connection with the local end using a fake AS number.
Carriers often use this command to change network deployment scenarios. For example, when carrier A acquires carrier B, the AS number of carrier B needs to be changed to that of carrier A because the two carriers are located in different ASs. However, during network merging, the BGP peers of carrier B located in other ASs may not modify local BGP configurations immediately. In this case, the connection with these peers will be interrupted.
To ensure smooth network merging, you can run the peer fake-as command on the ASBR of carrier B to set the AS number of carrier B to a fake AS number of carrier A so that BGP peers of carrier B can continue to establish connections using the fake AS number.
Example:
Set a 2-byte fake AS number for a peer.
[HUAWEI] bgp 100
[HUAWEI-bgp] peer 10.1.1.2 as-number 200
[HUAWEI-bgp] peer 10.1.1.2 fake-as 99

Other related questions:
Why are BGP connections reestablished after the peer connect-interface command is executed on S series switches
Currently, S series switches do not support BGP dynamic capability negotiation. Therefore, when capabilities of the BGP neighbor are changed, the BGP connection is automatically cut off and then the capabilities of the neighbor are renegotiated. If the peer connect-interface command is configured, the BGP session needs to be set up by designating the egress. Therefore, the source address of the TCP connection may be changed and the TCP connection needs to be re-established by using the new source address.

Why does an S series switch try to establish a BGP connection over 30s after peer configuration
For S series switches that support BGP, it is more complex to configure BGP than IGP. Besides peers and ASs, outbound interfaces, multiple hops, timers, and various capabilities need to be configured. At present, BGP does not support dynamic capability negotiation. Therefore, the changes of these parameters need to be negotiated again. To prevent the BGP peer relationship from being interrupted frequently, a proper timer is required. Ensure that related configurations are complete before the attempt of setting up a BGP connection. In RFC 4271, you are advised to set the value of the timer to 120s. On Huawei devices, the value of the timer is set to 32s.

How to configure BGP for S series switches
For information about how to configure basic BGP functions on a S series switch, visit Example for Configuring Basic BGP Functions

On an S series switch, after the reset bgp ipv4-address command is executed to reset BGP connections using the IPv4 unicast address family, why is the connection of BGP peers using the VPNv4 address family terminated
Q: After the reset bgp ipv4-address command is executed to reset the BGP connection of the unicast address family, why is the BGP connection of the same peers in the VPNv4 address family cut off? A: If the peers of two address families have the same addresses, the two address families share the same BGP session, that is, the same TCP connection. If one of the BGP connections is reset, the other is disconnected.

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