Configure 4-byte AS numbers

Configure Autonomous System (AS) numbers using the 4-byte format and represent the numbers in octets.

Before you begin

You cannot modify the global BGP configuration unless BGP is disabled.
Configure the local AS number at Global Router (VRF0) only.
Make sure that you define AS numbers in policies the same way that you configure them for the router. The AS list for the route policies accepts AS number only in the asplain format. If you create policies using asplain and configure the switch with asdot, the match will not occur.

About this task

Use BGP 4-byte AS numbers to ensure the continuity of loop-free inter-domain routing information between autonomous systems and to control the flow of BGP updates as 2-byte AS numbers will deplete soon. AS Plain notation format is the default and the preferred form of representing 4-byte AS numbers over the AS dot notation format.

You have an option to configure AS dot notation format as well. With AS dot notation, analyzing and troubleshooting any issues encountered becomes difficult as it is incompatible with the regular expressions used by most of the network providers.

If you enable 4-byte AS numbers, or the dotted octet notation, for the Global Router (VRF0), the configuration is inherited by user-defined VRFs. You cannot enable 4-byte AS numbers on individual user-defined VRFs.

Procedure

Enter Global Configuration mode:

enable

configure terminal
Disable BGP to change the AS number format.

no router bgp enable
Enable the 4-byte AS numbering format.

router bgp as–4–byte enable
To use the dotted octet notation, enable as-dot.

router bgp as-dot enable
Configure the 4-byte AS number and enable BGP. If you have enabled as-dot, enter the AS number in octet.

router bgp WORD<0–11> enable
Access Router BGP Configuration mode:

router bgp
Optional: Configure BGP confederation identifier.

bgp confederation identifier <0–4294967295>
Optional: Configure BGP confederation peers.

bgp confederation peers WORD<0–255>

Example

Disable BGP to change the AS number format.

Switch(config)# no router bgp enable

Enable the 4–byte AS numbering format.

Switch(config)# router bgp as-4-byte enable

To use the dotted octet notation, enable as-dot.

Switch(config)# router bgp as-dot enable

Configure the 4–byte AS number and enable BGP.

Switch(config)# router bgp 65536 enable

Variable Definitions

The following table defines parameters for the router bgp command.


Variable	Value
as-4-byte <enable>	Enables the switch for using 4 byte numbers for an autonomous system (AS). The default value is disable.
as-dot <enable>	Enables or disables representing AS numbers in octets. The default is disable so the switch uses the plain notation format. If you enable the 4-byte-as and as-dot parameters, enter numbers in the range of 1.0 to 65535.65535. The default value is disable. Note: This parameter is not supported with BGP+.
WORD <0–11> enable	Sets the local autonomous system (AS) number. You cannot change local-as when BGP is set to enable. To set a 2-byte local AS number, enter a local-as number in the range of 0 to 65535. To set a 4-byte local-as number, enable the 4-byte as variable and enter a number in the range of 0 to 4294967295. Note: If as-4-byte is set to false, the range for AS number is 0–65535 and if as-4-byte is set to true, the range is 0–4294967295. If you enable as-dot, enter the AS number in octets in the range of 1.0 to 65535.65535. Note: This parameter is not supported with BGP+.