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# 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 JUNOSe Multicast Routing Configuration Guide for information about 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—If you do not explicitly specify the address family, the router is configured to exchange unicast IPv4 addresses by default.
- Multicast IPv4—If you specify the multicast IPv4 address family, you can use BGP to exchange routing information about how to reach a multicast source instead of a unicast destination. For information about BGP multicasting commands, see Configuring BGP Routing . For a general description of multicasting, see JUNOSe Multicast Routing Configuration Guide.
- VPN IPv4—If you specify the VPN-IPv4 (also known as VPNv4) address family, you can configure the router to provide IPv4 VPN services over an MPLS backbone. These VPNs are often referred to as BGP/MPLS VPNs.
- Unicast IPv6—If you specify the IPv6 unicast address family, you can configure the router to exchange unicast IPv6 routes. For a description of IPv6, see JUNOSe IP, IPv6, and IGP Configuration Guide.
- Multicast IPv6—If you specify the multicast IPv6 address family, you can use BGP to exchange routing information about how to reach an IPv6 multicast source instead of an IPv6 unicast destination. For a general description of multicasting, see JUNOSe Multicast Routing Configuration Guide.
- VPN IPv6—If you specify the VPN-IPv6 address family, you can configure the router to provide IPv6 VPN services over an MPLS backbone. These VPNs are often referred to as BGP/MPLS VPNs.
- L2VPN—If you specify the L2VPN address family, you can configure the PE router for VPLS L2VPNs or VPWS L2VPNs to exchange layer 2 network layer reachability information (NLRI) for all VPLS or VPWS instances. Optionally, you can use the signaling keyword with the address-family command for the L2VPN address family to specify BGP signaling of L2VPN reachability information. Currently, you can omit the signaling keyword with no adverse effects. For a description of VPLS, see Configuring VPLS. For a description of VPWS, see Configuring VPWS.
- VPLS—If you specify the VPLS address family, you can configure the router to exchange layer 2 NLRI for a specified VPLS instance. For a description of VPLS, see Configuring VPLS.
- VPWS—If you specify the VPWS address family, you can configure the PE router to exchange layer 2 NLRI for a specified VPWS instance. For a description of VPWS, see Configuring VPWS.

As discussed in Understanding BGP Command Scope , 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 7 to configure parameters that affect the multicast address family globally. You can issue the commands listed in Table 9 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 8 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 or IPv6 addresses by creating the specified address family.
- IPv4 addresses can be exchanged in unicast, multicast, or VPN mode. IPv6 addresses can be exchanged in unicast mode.
- The default setting is to exchange IPv4 addresses in unicast mode from the default router.
- This command takes effect immediately.
- 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
  `
- Use the no version to disable the exchange of a type of prefix.
- See address-family.

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.
- See exit-address-family.

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.
- 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 routing table of the newly activated address family.

- Example
  `
  host1:vr1(config-router-af)#neighbor 192.168.1.158 activate
  `
- Use the no version to indicate that routes of the current address family must not be exchanged with the peer.
- See neighbor activate.

## 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.

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