Concept Guide

In BGP, routers with an established TCP connection are called neighbors or peers. After a connection is established, the neighbors
exchange full BGP routing tables with incremental updates afterward. In addition, neighbors exchange KEEPALIVE messages to maintain
the connection.
In BGP, neighbor routers or peers can be classied as internal or external. External BGP peers must be connected physically to one another
(unless you enable the EBGP multihop feature), while internal BGP peers do not need to be directly connected. The IP address of an EBGP
neighbor is usually the IP address of the interface directly connected to the router. First, the BGP process determines if all internal BGP
peers are reachable, then it determines which peers outside the AS are reachable.
Following is the sample conguration steps to enable BGP, congure a BGP router-id and network for a router. The same congurations
have to be repeated with appropriate changes in the IP addresses for a peer or router to achieve BGP session between two devices. In the
below conguration example, no address family is congured. So, the routing information for the IPv4 unicast address family is advertised
by default.
1 Assign an AS number and enter ROUTER BGP mode.
CONFIGURATION mode
router bgp as-number
• as-number: from 0 to 65535 (2 Byte) or from 1 to 4294967295 (4 Byte) or 0.1 to 65535.65535 (Dotted format).
Only one AS is supported per system.
NOTE: If you enter a 4-Byte AS number, 4-Byte AS support is enabled automatically.
2 Add a BGP neighbor or peer and AS number.
CONFIG-ROUTER-BGP mode
neighbor {ip-address | ipv6-address| peer-group name} remote-as as-number
• ip-address: IPv4 address of the neighbor
• ipv6-address: IPv6 address of the neighbor
• peer-group name: Name of the peer group. It can contain 16 characters.
• as-number: from 0 to 65535 (2 Byte) or from 1 to 4294967295 (4 Byte) or 0.1 to 65535.65535 (Dotted format)
NOTE
: Neighbors that are dened using the neighbor remote-as command in the CONFIGURATION-ROUTER-BGP
mode exchange IPv4 unicast address prexes only.
3 Enable the BGP neighbor.
CONFIG-ROUTER-BGP mode
neighbor {ip-address | ipv6–address | peer-group-name} no shutdown
Example conguration steps to enable BGP
NOTE
: When you change the conguration of a BGP neighbor, always reset it by entering the clear ip bgp * command in
EXEC Privilege mode.
To view the BGP conguration, enter show config in CONFIGURATION ROUTER BGP mode. To view the BGP status, use the show
ip bgp summary command in EXEC Privilege mode. The example shows that the summary with a 4-byte AS number using the show
ip bgp summary command (displays a 4–byte AS number in bold).
Following is the conguration steps:
DellEMC# configure terminal
DellEMC(conf)# router bgp 65550
DellEMC(conf-router_bgp)# neighbor 20.20.20.1 remote-as 20
DellEMC(conf-router_bgp)# neighbor 20.20.20.1 no shutdown
DellEMC(conf-router_bgp)#exit
DellEMC(conf)#
Border Gateway Protocol (BGP)
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