Enabling As4 Numbers - Brocade Communications Systems FastIron SX 800 Configuration Manual

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, a peer group, or globally for the entire device, according to
the following bottom-up hierarchy:
• If a neighbor has no configuration for AS4s but it belongs to a peer group, the neighbor uses the configuration from the peer
group. For example, if you configure a neighbor but do not include a specification for AS4s, one of the following applies:
– The neighbor uses the AS4 configuration for a peer group if it belongs to a peer group.
– The neighbor uses the device configuration if it does not belong to a peer group or the peer group has no AS4
configuration.
• If a peer group has no configuration for AS4s, it can use the global configuration of the device. If the device has no configuration
for AS4s, then a neighbor or peer group without a configuration for AS4s use the device default--no announcement or
negotiation of AS4s.
• If a neighbor belongs to peer group with an AS4 configuration but you want that neighbor to be disabled or have a different AS4
configuration, the neighbor AS4 configuration overrides the peer group configuration. For example, you can ensure that
neighbor has no AS4 announcement and negotiation activity even though the peer group is enabled for AS4 capability.
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. For example, you can use a CLI
command to disable AS4s on a neighbor that is a member of a peer group that is enabled for AS4s.
Normally, AS4s are sent only to a device, peer group, or neighbor that is similarly configured for AS4s. If a AS4 is configured for a local-
autonomous systemS, 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-byte 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, a peer group, and a neighbor. For global configuration, the capability command in the BGP4
configuration context enables or disables AS4 support. For a peer group or a neighbor, capability is a keyword for the neighbor
command. In addition to enabling AS4s for a neighbor or a peer group, 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
Neighbor configuration of AS4s section illustrates this capability.
Global AS4 configuration
To enable AS4s globally, use the capability command in the BGP4 configuration context as shown.
device(config-bgp)# capability as4 enable
Syntax: [no] capability as4 enable | disable
The no form of the capability command deletes the announcement and negotiation configuration of AS4s (if it has been enabled) at the
global level. Using the regular form of the command with the disable keyword has the same effect on the global configuration. Disabling
or using the no form of the command does not affect the configuration at the level of a peer or neighbor.
FastIron Ethernet Switch Layer 3 Routing
53-1003627-04
Four-byte Autonomous System Numbers (AS4)
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