Bgp Configuration - Cisco ASR 9000 Series Routing Configuration Manual

Implementing BGP
clear bgp nexthop performance-statistics command ensures that the cumulative statistics associated with
the processing part of the next-hop show command can be cleared to help in monitoring. The clear bgp
nexthop registration command performs an asynchronous registration of the next hop with the RIB. See the
BGP Commands on Cisco ASR 9000 Series Router module of Cisco ASR 9000 Series Aggregation Services
Router Routing Command Referencefor information on the next-hop show and clear commands.
The debug bgp nexthop command displays information on next-hop processing. The out keyword provides
debug information only about BGP registration of next hops with RIB. The in keyword displays debug
information about next-hop notifications received from RIB. The out keyword displays debug information
about next-hop notifications sent to the RIB. See the BGP Debug Commands on Cisco ASR 9000 Series
Aggregation Services Router module of Cisco ASR 9000 Series Aggregation Services Router Routing Debug
Command Reference.
Autonomous System Number Formats in BGP
Autonomous system numbers (ASNs) are globally unique identifiers used to identify autonomous systems
(ASs) and enable ASs to exchange exterior routing information between neighboring ASs. A unique ASN is
allocated to each AS for use in BGP routing. ASNs are encoded as 2-byte numbers and 4-byte numbers in
BGP.
2-byte Autonomous System Number Format
The 2-byte ASNs are represented in asplain notation. The 2-byte range is 1 to 65535.
4-byte Autonomous System Number Format
To prepare for the eventual exhaustion of 2-byte Autonomous System Numbers (ASNs), BGP has the capability
to support 4-byte ASNs. The 4-byte ASNs are represented both in asplain and asdot notations.
The byte range for 4-byte ASNs in asplain notation is 1-4294967295. The AS is represented as a 4-byte
decimal number. The 4-byte ASN asplain representation is defined in draft-ietf-idr-as-representation-01.txt.
For 4-byte ASNs in asdot format, the 4-byte range is 1.0 to 65535.65535 and the format is:
high-order-16-bit-value-in-decimal . low-order-16-bit-value-in-decimal
The BGP 4-byte ASN capability is used to propagate 4-byte-based AS path information across BGP speakers
that do not support 4-byte AS numbers. See draft-ietf-idr-as4bytes-12.txt for information on increasing the
size of an ASN from 2 bytes to 4 bytes. AS is represented as a 4-byte decimal number
as-format Command
The as-format command configures the ASN notation to asdot. The default value, if the as-format command
is not configured, is asplain.

BGP Configuration

BGP in Cisco IOS XR software follows a neighbor-based configuration model that requires that all
configurations for a particular neighbor be grouped in one place under the neighbor configuration. Peer groups
are not supported for either sharing configuration between neighbors or for sharing update messages. The
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.3.x
Autonomous System Number Formats in BGP
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