BGP vs MBGP

Currently BGP is running in version 4, which has been published in 2006 (RFC 4271). By default, BGPv4 only supports IPv4 unicast prefixes, But BGP can do much more than carrying IPv4 prefixes only. RFC 4760 Multiprotocol extensions for BGPv4 has been developed in order to enhance the capacity of carrying routing related information other than carrying ipv4 only.

Multiprotocol Extensions for BGPv4 added some new attributes.


  • Multiprotocol Reachable NLRI (MP_REACH_NLRI): It carry set of reachable destination with next-hop information.
  • Multiprotocol Unreachable NLRI (MP_UNREACH_NLRI): It carry set of unreachable destinations.

Note : –MP_REACH_NLRI” and “MP_UNREACH_NLRI” are optional and Non-transitive attribute, because of this if neighbor doesn’t support the multiprotocol capabilities, it will just ignore information carried in these attributes and will not pass it to other BGP neighbor.

Both “MP_REACH_NLRI” and “MP_UNREACH_NLRI” contains two fields.

  • Address family identifier (AFI): use for identifies address types.
Example to check MBGP AFI types

R1(config)#router bgp 65001

R1(config-router)# address-family ?

ipv4            Address family

ipv6            Address family

l2vpn          Address family

rtfilter         Address family

vpnv4        Address family

vpnv6        Address family

  • Subsequent address family identifier (SAFI): Use for provide further address family information.

Example to check MBGP SAFI types

R1(config-router)#address-family ipv4 ?

mdt                  Address Family modifier

multicast          Address Family modifier

mvpn               Address Family modifier

unicast            Address Family modifier

vrf                    Specify parameters for a VPN Routing/Forwarding instance

Multiprotocol BGP address family types

  • Unicast: – IPv4, IPv6
  • Multicast: – IPv4, IPv6
  • Virtualization: – VPNv4, VPNv6, L2VPN, VPLS, MCAST-VPN, MDT, Encapsulation, Tunnel, 4over6, 6over4.

MBGP configuration Example

Step 1: – First define address family under BGP configuration.

R1(config-router)#address-family {ipv4 | ipv6} {Unicast | Multicast}

Step 2: – Activate neighbor session.

R1(config-router-af)#neighbor {ipv6-address| IPv6-address | Peer-group-name} activate

Step 3: – Configure policies and networks.

Example of IPv4 unicast address family

R1(config-router)#address-family ipv4 unicast

R1(config-router-af)#network <IPv4-address> mask <Subnetmask>

Step 4: – exit address family configuration.

R1(config-router-af)#exit-address-family
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