Dell PowerEdge FN I/O Module Configuration Guide 9.10(0.0)

The 4-Byte support is advertised as a new BGP capability (4-BYTE-AS) in the OPEN message. If a 4-Byte BGP speaker has sent and received this capability from another speaker, all the messages will be 4-octet. The behavior of a 4-Byte BGP speaker is different with the peer depending on whether the peer is a 4-Byte or 2-Byte BGP speaker.

Where the 2-Byte format is 1-65535, the 4-Byte format is 1-4294967295. Enter AS numbers using the traditional format. If the ASN is greater than 65535, the dot format is shown when using the show ip bgp commands. For example, an ASN entered as 3183856184 appears in the show commands as 48581.51768; an ASN of 65123 is shown as 65123. To calculate the comparable dot format for an ASN from a traditional format, use ASN/65536. ASN%65536.

Traditional Format	DOT Format
65001	0.65501
65536	1.0
100000	1.34464
4294967295	65535.65535

When creating Confederations, all the routers in a Confederation must be either 4-Byte or 2-Byte identified routers. You cannot mix them.

Configure 4-byte AS numbers with the four-octet-support command.