Configuring BGP Multicasting

The BGP multiprotocol extensions (MP-BGP) enable BGP to carry IP multicast routes used by the Protocol Independent Multicast (PIM) to build data distribution trees (see ERX Routing Protocols Configuration Guide, Vol. 1, Chapter 3, Configuring IP Multicasting for information on PIM). You can configure a multicast routing topology different from your unicast topology to achieve greater control over network resources. This application of MP-BGP is often referred to as multicast BGP (MBGP).

The BGP multiprotocol extensions specify that BGP can exchange information within different types of address families:

• Unicast IPv4 - When you enable BGP, the system employs unicast IPv4 addresses by default. You must specify an address family other than unicast IPv4 for the new features.
• Multicast IPv4 - If you specify the multicast IPv4 address family, you can configure the system to exchange routes to multicast sources (as opposed to routes to unicast destinations).
• VPN-IPv4 - If you specify the VPN-IPv4 address family, sometimes referred to as VPNv4, you can configure the system to provide IPv4 VPN services via an MPLS backbone.

As discussed in Understanding BGP Command Scope (p 1-15), BGP configuration commands fall into five categories. If you specify the multicast address family, from within the Address Family Configuration mode you can issue the commands listed in Table 1-4 to configure parameters that affect the multicast address family globally. You can issue the commands listed in Table 1-6 to configure a peer or peer group that you have activated in the multicast address family without affecting those configuration parameters for any other address family within which the peer or peer group is activated.

If you issue any of the commands listed in Table 1-5 from within the default IPv4 unicast address family to configure a peer or peer group, you can apply those configuration values to the same entity in the multicast address family by activating the peer or peer group in the multicast address family.

Example

To add a peer to the multicast routing table, first add the peer to the unicast routing table, and then copy it to the multicast routing table.

host1(config)#router bgp 22

host1(config-router)#neighbor 192.168.55.122 remote-as 33

host1(config-router)#address-family ipv4 multicast

host1(config-router-af)neighbor 192.168.55.122 activate

    address-family

• Use to configure the router to exchange IPv4 addresses in unicast, multicast, or VPN mode.
• The default setting is to exchange IPv4 addresses in unicast mode from the default router.
• Examples

host1:vr1(config-router)#address-family ipv4 multicast

host1:vr1(config-router)#address-family vpnv4 

host1:vr1(config-router)#address-family ipv4 unicast vrf vr2

• This command takes effect immediately.
• Use the no version to disable the exchange of a type of prefix.

    exit-address-family

• Use to exit Address Family Configuration mode and access Router Configuration mode.
• Example

host1:vr1(config-router-af)#exit-address-family

• There is no no version.

    neighbor activate

• Use to specify a peer with which routes of the current address family are exchanged.
• A peer can be activated in more than one address family. By default, a peer is activated only for the IPv4 unicast address family.
• The peer must be created in unicast IPv4 or VPN IPv4 before you can activate it in another address family.
• If you specify a BGP peer group by using the peerGroupName argument, all the members of the peer group inherit the characteristic configured with this command unless it is overridden for a specific peer.
• The address families that are actively exchanged over a BGP session are negotiated when the session is established.
• Example

host1:vr1(config-router-af)#neighbor 192.168.1.158 activate

• This command takes effect immediately. If dynamic capability negotiation was not negotiated with the peer, the session is automatically bounced so that the exchanged address families can be renegotiated in the open messages when the session comes back up.

If dynamic capability negotiation was negotiated with the peer, BGP sends a capability message to the peer to advertise or withdraw the multiprotocol capability for the address family in which this command is issued. If a neighbor is activated, BGP also sends the full contents of the BGP RIB of the newly activated address family.

• Use the no version to indicate that routes of the current address family should not be exchanged with the peer.

Monitoring BGP Multicast Services

To display values from the BGP multicast routing table, use the show BGP commands with the ipv4 multicast keyword. For more information about displaying BGP parameters, see Monitoring BGP in this chapter.