Concept Guide
NOTE: It is possible to congure BGP peers that exchange both unicast and multicast network layer reachability information
(NLRI), but you cannot connect multiprotocol BGP with BGP. Therefore, you cannot redistribute multiprotocol BGP routes into
BGP.
MBGP for IPv4 Multicast
PIM feature uses IPv4 multicast routing for data distribution. MBGP provides a link that is dedicated specic to multicast trac. MBGP
also allows a unicast routing apart from the multicast routing. A multicast routing protocol, such as PIM, uses both the unicast and
multicast BGP database to form a routing table for unicast and multicast. You can congure BGP peers that exchange both unicast and
multicast Network Layer Reachability Information (NLRI) in which MBGP routes is redistributed into BGP. The default is IPv4 unicast.
BGP Address Family model
Dell EMC Networking OS supports BGP address family identier (AFI) with MBGP to provide scalability for multiple AFI and subsequent
address family identier (SAFI) congurations. MBGP carries routing information for address families (IPv4 and IPv6) of multiple network-
layer protocols. Each address family has a separated BGP database, so that you can congure BGP policy based on address family.
IPv4 and IPv6 address family
The IPv4 address family conguration in Dell EMC Networking OS is used for identifying routing sessions for protocols that use IPv4
address. You can specify multicast within the IPv4 address family. The default of address family conguration is IPv4 unicast. You can
congure the VRF instances for IPv4 address family conguration.
The IPv6 address family conguration is used for identifying routing sessions for protocols that use IPv6 address. You can specify unicast
within the IPv6 address family. You can congure the VRF instances for IPv6 address family conguration.
Sessions and Peers
When two routers communicate using the BGP protocol, a BGP session is started. The two end-points of that session are Peers. A Peer is
also called a Neighbor.
Establish a Session
Information exchange between peers is driven by events and timers. The focus in BGP is on the trac routing policies.
In order to make decisions in its operations with other BGP peers, a BGP process uses a simple nite state machine that consists of six
states: Idle, Connect, Active, OpenSent, OpenConrm, and Established. For each peer-to-peer session, a BGP implementation tracks which
of these six states the session is in. The BGP protocol denes the messages that each peer should exchange in order to change the
session from one state to another.
State
Description
Idle BGP initializes all resources, refuses all inbound BGP connection attempts, and initiates a TCP connection to the
peer.
Connect In this state the router waits for the TCP connection to complete, transitioning to the OpenSent state if successful.
If that transition is not successful, BGP resets the ConnectRetry timer and transitions to the Active state when the
timer expires.
Active The router resets the ConnectRetry timer to zero and returns to the Connect state.
176 Border Gateway Protocol (BGP)