Concept Guide

Example of the Running Conguration When AS Notation is Disabled
AS NOTATION DISABLED
DellEMC(conf-router_bgp)#
no bgp asnotation
DellEMC(conf-router_bgp)#sho conf
!
router bgp 100
bgp four-octet-as-support
neighbor 172.30.1.250 local-as 65057
<output truncated>
DellEMC(conf-router_bgp)#do sho ip bgp
BGP table version is 28093, local router ID is 172.30.1.57
AS4 SUPPORT DISABLED
DellEMC(conf-router_bgp)#no bgp four-octet-as-support
DellEMC(conf-router_bgp)#sho conf
!
router bgp 100
neighbor 172.30.1.250 local-as 65057
DellEMC(conf-router_bgp)#do show ip bgp
BGP table version is 28093,
local router ID is 172.30.1.57
Four-Byte AS Numbers
You can use the 4-Byte (32-bit) format when conguring autonomous system numbers (ASNs).
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 dierent 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 identied routers. You cannot mix them.
Congure 4-byte AS numbers with the bgp four-octet-as-support command.
Multiprotocol BGP
MBGP is an extensison of BGP to carry routing information for multiple network-layer protocols such as IPv4 unicast and multicast, and
IPv6 unicast. MBGP provides support for multiple network layer protocol address families that allows to dene independent policy and
peering congurations. MBGP carries dierent set of routes depending on the protocol. It carries routing information for IPv4 multicast and
IPv6 unicast routes. Multiprotocol extensions for BGP (MBGP) is dened in IETF RFC 2858. MBGP allows dierent types of address
families to be distributed in parallel.
MBGP allows information about the topology of the IP multicast-capable routers to be exchanged separately from the topology of normal
IPv4 and IPv6 unicast routers. It allows a multicast routing topology dierent from the unicast routing topology.
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Border Gateway Protocol (BGP)