Brocade Virtual ADX Switch and Router Guide (Supporting ADX v03.1.00) - Manual (Page 238)

224 Brocade Virtual ADX Switch and Router Guide
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Requiring the first AS to be the neighbor AS
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The hierarchy for enforcement of this feature is: a neighbor will try to use the enforce-first-as value
if one is configured; if none is configured, enforcement is simply that of the global configuration
(which is disabled by default).
To enable this feature globally, enter the enforce-first-as command at the BGP4 configuration level
of the CLI.
Virtual ADX(config-bgp)# enforce-first-as
Syntax: [no] enforce-first-as
To enable this feature for a specific neighbor, enter the following command at the BGP4
configuration level.
Virtual ADX(config-bgp)# neighbor 10.1.1.1 enforce-first-as enable
Syntax: [no] neighbor ip-address enforce-first-as [enable | disable]
The ip-address value is the IP address of the neighbor.
When the first-as requirement is enabled, its status appears in the output of the show running
configuration command. The optional last keyword choice of enable or disable lets you specify
whether the output of the show running configuration command includes the configuration of the
first-as requirement. This option allows the show running configuration command output to show
what is actually configured.
The following example shows a running configuration with the first-as enforcement items in bold.
Virtual ADX(config)# router bgp
BGP4: Please configure 'local-as' parameter in order to enable BGP4.
Virtual ADX(config-bgp-router)# local-as 1
Virtual ADX(config-bgp-router)# enforce-first-as
Virtual ADX(config-bgp-router)# neighbor A.B.C.D remote-as 2
Virtual ADX(config-bgp-router)# neighbor A.B.C.D enforce-first-as disable
Virtual ADX(config-bgp-router)# neighbor 192.168.1.2 enforce-first-as enable
Enabling fast external fallover
BGP4 devices rely on KEEPALIVE and UPDATE messages from neighbors to signify that the
neighbors are alive. For BGP4 neighbors that are two or more hops away, such messages are the
only indication that the BGP4 protocol has concerning the alive state of the neighbors. As a result,
if a neighbor becomes non-operational, the device waits until the Hold Time expires or the TCP
connection fails before concluding that the neighbor is not operational and closing its BGP4
session and TCP connection with the neighbor.
The device waits for the Hold Time to expire before ending the connection to a directly-attached
BGP4 neighbor that becomes non-operational.
For directly-attached neighbors, the device immediately senses loss of a connection to the
neighbor from a change of state of the port or interface that connects the device to the neighbor.
For directly-attached EBGP neighbors, the device uses this information to immediately close the
BGP4 session and TCP connection to locally attached neighbors that become non-operational.
NOTE
The fast external fallover feature applies only to directly attached EBGP neighbors. The feature does
not apply to IBGP neighbors.