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BGP and BGP4+ Introduction
Software Reference Supplement for SwitchBlade® x8112, x908, x900 and x610 Series Switches
C613-50032-01 REV D AlliedWare Plus
TM
Operating System - Software Version 5.4.3-2.6 1.39
How to remove private AS numbers for BGP
There are public and private AS numbers, in the same way there are public and private IP
addresses. Like the private IP addresses that you cannot send to the Internet, you cannot
send private AS numbers to the Internet. This functionality enables you to remove them.
Public AS numbers range from 1 to 64,511. Private AS numbers range for 64,512 and
65,535. Private AS numbers are used to divide large ASs into smaller multiple ASs for eBGP.
ISPs may assign private AS numbers to save public AS number usage. When you receive
private AS numbers, you need to remove them before you send updates to the Internet. To
remove private AS numbers for BGP, use this command in the Router Configuration mode:
For the filtering to apply, both peering devices must be set to use either 2-byte or
extended 4- byte ASN (with the same ASN type set on both peers). For example, if a device
(which defaults to use a 4-byte ASN), is peered with a device that defaults to a 2-byte ASN,
then the device using a 2-byte ASN device also needs to be configured with the command
bgp extended-asn-cap for the filtering to apply.
The neighbor remove-private-AS (BGP) command is not available in IPv6 Address
Family Configuration mode for BGP4+. This command is only available in Router
Configuration mode for BGP.
Verify the application of this command with the show running-config and show ip bgp
commands. See sample verification output in the following sections:
■ How to remove BGP filtering for private AS numbers
■ How to apply BGP filtering for private AS numbers.
awplus(config-router)#
neighbor <neighborid>
remove-private-AS
This command removes private AS numbers for BGP in Router
Configuration mode. This command is not supported for
BGP4+ in IPv6 Address Family Configuration mode.
This command removes a private AS number and makes an
update packet with a public AS number as the AS path
attribute. So only public AS numbers are entered in Internet
BGP routing tables, and private AS numbers are not entered in
Internet BGP tables.