Administrator Guide

To turn off the default, use the no bgp enforce-first-as command.
Defaults Enabled.
Command Modes ROUTER BGP
Command History
Version Description
9.9(0.0) Introduced on the C9010.
9.2(1.0) Introduced on the Z9500.
8.2.1.0 Introduced on the E-Series ExaScale.
7.4.1.0 Introduced
Usage Information
This is enabled by default, that is for all updates received from EBGP peers, BGP ensures that the first AS of the
first AS segment is always the AS of the peer. If not, the update is dropped and a counter is incremented. Use the
show ip bgp neighbors command to view the “failed enforce-first-as check” counter.
If you disable enforce-first-as, you can view it using the show ip protocols command.
Related
Commands
• show ip bgp neighbors – views the information exchanged by BGP neighbors.
• show ip protocols – views information on routing protocols.
bgp fast-external-fallover
Enable the fast external failover feature, which immediately resets the BGP session if a link to a directly connected external peer fails.
C9000 Series
Syntax
bgp fast-external-fallover
To disable fast external fallover, use the no bgp fast-external-fallover command.
Defaults Enabled.
Command Modes ROUTER BGP
Command History
Version Description
9.9(0.0) Introduced on the C9010.
9.2(1.0) Introduced on the Z9500.
8.2.1.0 Introduced on the E-Series ExaScale.
7.4.1.0 Introduced
Usage Information The bgp fast-external-fallover command appears in the show config command output.
bgp four-octet-as-support
Enable 4-byte support for the BGP process.
C9000 Series
Syntax
bgp four-octet-as-support
To disable fast external fallover, use the no bgp four-octet-as-support command.
Defaults Disabled (supports 2-Byte format).
Command Modes ROUTER BGP
Border Gateway Protocol 429