Four-byte autonomous system numbers (as4), Enabling as4 numbers – Brocade Virtual ADX Switch and Router Guide (Supporting ADX v03.1.00) User Manual
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Brocade Virtual ADX Switch and Router Guide
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Four-byte Autonomous System Numbers (AS4)
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Virtual ADX(config-bgp)# compare-routerid
Syntax: [no] compare-routerid
For more information, refer to
“How BGP4 selects a path for a route”
Four-byte Autonomous System Numbers (AS4)
This section describes the reasons for enabling four-byte autonomous system numbers (AS4s).
AS4s are supported by default. You can specify and view AS4s by default and using the enable
facility described in this section. However, because not all devices in a network are always capable
of utilizing AS4s, the act of enabling them on the local device initiates a facility for announcing the
capability and negotiating its use with neighbors. If you do not enable AS4s on a device, other
devices do not know that this device is sending them.
The system uses a hierarchy to prioritize the utilization of the AS4 capability. The prioritization
depends on the CLI configuration commands. AS4s can be enabled and configured at the level of a
neighbor or globally for the entire device:
NOTE
The configuration for AS4 can be enabled, disabled, or can have no explicit configuration.
CLI commands allow you to disable AS4s on an entity whose larger context has AS4s enabled.
Refer to
Normally, AS4s are sent only to a device or neighbor that is similarly configured for AS4s. If a AS4 is
configured for a local-AS, the system signals this configuration by sending AS_TRANS in the My
Autonomous System field of the OPEN message. However, if the AS4 capability for a neighbor is
disabled, the local device does not send the four-octet Autonomous System number capability to
the neighbor.
Enabling AS4 numbers
This section describes how to enable the announcement and negotiation of AS4s and describes
the different types of notation that you can use to represent a AS4.
You can enable AS4s on a device and a neighbor. For global configuration, the capability command
in the BGP4 configuration context enables or disables AS4 support. For a neighbor, capability is a
keyword for the neighbor command. In addition to enabling AS4s for a neighbor, you can also use
the combination of the capability keyword and the optional enable or disable keyword to disable
this feature in a specific case where the AS4s are enabled for a larger context. The
section illustrates this capability.
Global AS4 configuration
To enable AS4s globally, use the capability command in the BGP4 configuration context, as shown.
Virtual ADX(config-bgp)# capability as4 enable
Syntax: [no] capability as4 enable | disable