Administrator Guide

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 configuring 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
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 bgp four-octet-as-support command.
BGP router ID
A router ID is used to identify neighbors configured with BGP. The BGP router ID is a user given ID to a BGP router, which
is unique 32-bit value IPv4 address. The router ID is the highest IP address of the Loopback interface and if no Loopback
interfaces are configured, Dell EMC Networking OS selects the highest IP address of a physical interface on the router as the
router ID.
Sessions and Peers
When two routers communicate using the BGP protocol, a BGP session is started. The two end-points of that session are called
neighbors or peers. A local device does not identify a BGP peer automatically. You have to manually configure the connections
between BGP running devices. BGP uses TCP connection to communicate with another BGP neighbor. After establishing a TCP
connection between the peers, each peer exchange route information with other peer.
Establish a Session
Information exchange between peers is driven by events and timers. The focus in BGP is on the traffic routing policies.
In order to make decisions in its operations with other BGP peers, a BGP process uses a simple finite state machine that
consists of six states: Idle, Connect, Active, OpenSent, OpenConfirm, and Established. For each peer-to-peer session, a BGP
implementation tracks which of these six states the session is in. The BGP protocol defines the messages that each peer should
exchange in order to change the session from one state to another.
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Border Gateway Protocol (BGP)