Concept Guide

State Description
OpenSent After successful OpenSent transition, the router sends an Open message and waits for one in return.
OpenConrm After the Open message parameters are agreed between peers, the neighbor relation is established and is in the
OpenConrm state. This is when the router receives and checks for agreement on the parameters of open
messages to establish a session.
Established Keepalive messages are exchanged next, and after successful receipt, the router is placed in the Established state.
Keepalive messages continue to be sent at regular periods (established by the Keepalive timer) to verify
connections.
After the connection is established, the router can now send/receive Keepalive, Update, and Notication messages to/from its peer.
Peer Groups
Peer groups are neighbors grouped according to common routing policies. They enable easier system conguration and management by
allowing groups of routers to share and inherit policies.
Peer groups also aid in convergence speed. When a BGP process needs to send the same information to a large number of peers, the BGP
process needs to set up a long output queue to get that information to all the proper peers. If the peers are members of a peer group
however, the information can be sent to one place and then passed onto the peers within the group.
Implementing BGP global and address family
Implementing BGP is splitted as global and address family conguration.
BGP conguration command levels are grouped as high level and address family conguration. All independent commands are grouped at
the beginning of the conguration and followed by separate sub commands specic to each address family.
Following is the order of BGP conguration:
• Global conguration — General conguration that is applied to BGP. For example, conguring BGP timer, Adding additional BGP paths,
etc.
• Address family conguration — Congurations that are applied to a specic address family.
The BGP address family model consists of three address families such as IPv4 unicast, IPv4 multicast, and IPv6 unicast. The default
address family is IPv4 unicast. The neighbors congured under CONFIGURATION-ROUTER-BGP mode is considered to be IPv4 unicast
neighbor. To congure a neighbor for IPv4 multicast or IPv6 unicast, you have to explicity activate the neighbor in the respective address
family conguration, as shown the following example conguration.
Example of BGP conguration command levels
Following is an example conguration, which explains the neighbor conguration for all the address families.
DellEMC(conf)#router bgp 10
DellEMC(conf-router_bgp)#neighbor 20.20.20.1 remote-as 200
DellEMC(conf-router_bgp)#neighbor 20.20.20.1 no shutdown
DellEMC(conf-router_bgp)#neighbor 2001::1 remote-as 200
DellEMC(conf-router_bgp)#neighbor 2001::1 no shutdown
DellEMC(conf-router_bgp)#address-family ipv4 multicast
DellEMC(conf-router_bgp_af)#neighbor 20.20.20.1 activate
DellEMC(conf-router_bgp_af)#exit
DellEMC(conf-router_bgp)#address-family ipv6 unicast
DellEMC(conf-router_bgpv6_af)#neighbor 2001::1 activate
DellEMC(conf-router_bgpv6_af)#exit
Border Gateway Protocol (BGP)
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