Connectivity Guide

neighbors or peers. After a connection establishes, the neighbors exchange full BGP routing tables with incremental updates afterward.
Neighbors also exchange the KEEPALIVE messages to maintain the connection.
You can classify BGP neighbor routers or peers as internal or external. Connect EBGP peers directly, unless you enable EBGP multihop —
IBGP peers do not need direct connection. The IP address of an EBGP neighbor is usually the IP address of the interface directly
connected to the router. The BGP process rst determines if all internal BGP peers are reachable, then it determines which peers outside
the AS are reachable.
1 Assign an AS number, and enter ROUTER-BGP mode from CONFIGURATION mode, from 1 to 65535 for 2-byte, 1 to 4294967295 for
4-byte. Only one AS number is supported per system. If you enter a 4-byte AS number, 4-byte AS support is enabled automatically.
router bgp as-number
2 Enter a neighbor in ROUTER-BGP mode.
neighbor ip-address
3 Add a remote AS in ROUTER-NEIGHBOR mode, from 1 to 65535 for 2-byte or 1 to 4294967295 for 4-byte.
remote-as as-number
4 Enable the BGP neighbor in ROUTER-NEIGHBOR mode.
no shutdown
5 (Optional) Add a description text for the neighbor in ROUTER-NEIGHBOR mode.
description text
To reset the conguration when you change the conguration of a BGP neighbor, use the clear ip bgp * command. To view the BGP
status, use the show ip bgp summary command.
Congure BGP
OS10# configure terminal
OS10(config)# router bgp 100
OS10(config-router-bgp-100)# neighbor 5.1.1.1
OS10(config-router-neighbor)# remote-as 1
OS10(config-router-neighbor)# description n1_abcd
OS10(config-router-neighbor)# exit
OS10(config-router-bgp-100)# template t1
OS10(config-router-template)# description peer_template_1_abcd
View BGP summary with 2-byte AS number
OS10# show ip bgp summary
BGP router identifier 202.236.164.86 local AS number 64901
Neighbor AS MsgRcvd MsgSent Up/Down State/Pfx
120.10.1.1 64701 664 662 04:47:52 established 12000
View BGP summary with 4-byte AS number
OS10# show ip bgp summary
BGP router identifier 11.1.1.1, local AS number 4294967295
BGP local RIB : Routes to be Added 0, Replaced 0, Withdrawn 0
1 neighbor(s) using 8192 bytes of memory
Neighbor AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/Pfx
5.1.1.2 4294967295 0 0 0 0 0 00:00:00 Active
For the router ID, the system selects the rst congured IP address or a random number. To view the status of BGP neighbors, use the
show ip bgp neighbors command. For BGP neighbor conguration information, use the show running-config bgp command.
The example shows two neighbors — one is an external BGP neighbor; and the other is an internal BGP neighbor. The rst line of the
output for each neighbor displays the AS number and states if the link is external or internal.
The third line of the show ip bgp neighbors output contains the BGP state. If anything other than established displays, the neighbor
is not exchanging information and routes. For more information, see
IPv6 commands.
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