Understanding NLRI Keywords and Address Families

MBGP was introduced in Cisco IOS Release 11.1(20)CC and Cisco IOS Release 12.0(2)S prior to it being integrated into Cisco IOS Release 12.1. In Cisco IOS Release 11.1(20)CC and later releases and Cisco IOS Release 12.0(2)S and later releases, the Cisco IOS software uses NLRI keywords to enable MBGP over a BGP session and to populate unicast BGP prefixes in the unicast database and multicast BGP prefixes in the multicast database. In Cisco IOS Release 12.1, the Cisco IOS software uses separate address families to enable MBGP over a BGP session and to populate unicast BGP prefixes in the unicast database and multicast BGP prefixes in the multicast database.

Cisco IOS Release 12.1 does not support the NLRI keywords. However, for backward compatibility, the NLRI keyword configuration of a Cisco router is automatically converted to an address family configuration when a router is upgraded to Cisco IOS Release 12.1. The following example shows an NLRI keyword configuration for a Cisco router that is running Cisco IOS Release 12.0(8)S:

The following example shows the resulting address family configuration after the same router is upgraded to Cisco IOS Release 12.1:

Although supported in Cisco IOS Release 12.1, the following sections do not explain how to configure the BGP-4 extensions for Virtual Private Network (VPN) address family prefixes. Configuring VPN address family prefixes will be explained in a later release of the Cisco IOS IP Configuration Guide and the Cisco IOS IP Command Reference, Volume 2 of 3: Routing Protocols.

Configuring an MBGP Peer

To configure MBGP between two routers, use the following commands beginning in global configuration mode:

By default, neighbors that are defined using the neighbor remote-as command in router configuration mode exchange only unicast address prefixes. To exchange other address prefix types, such as multicast and VPNv4, neighbors must also be activated using the neighbor activate command in address family configuration mode, as shown.

See the MBGP Peer Example section for MBGP peer configuration examples.

Configuring an MBGP Peer Group

To configure a peer group to perform MBGP routing, use the following commands beginning in global configuration mode:

By default, neighbors that are defined using the neighbor remote-as command in router configuration mode exchange only unicast address prefixes. To exchange other address prefix types, such as multicast and VPNv4, neighbors must also be activated using the neighbor activate command in address family configuration mode, as shown.

• Peer groups that are defined in router configuration mode using the neighbor peer-group command exchange only unicast address prefixes by default. To exchange other address prefix types, such as multicast, peer groups must be defined in address family configuration mode using the neighbor activate command, as shown.

Members of a peer group automatically inherit the address prefix configuration of the peer group.

Refer to the section “Configure BGP Peer Groups” of the “Configuring BGP” chapter in the Cisco IOS IP Command Reference, Volume 2 of 3: Routing Protocols for information and instructions on assigning options to the peer group and making a BGP or MBGP neighbor a member of the peer group.

Advertising Routes into MBGP

To advertise (inject) a network number and mask into MBGP, use the following commands beginning in global configuration mode:

Networks that are defined in router configuration mode using the network command are injected into the unicast database by default. To inject a network into another database, such as the multicast database, the network must be defined in address family configuration mode using the network command, as shown.

To redistribute Distance Vector Multicast Routing Protocol (DVMRP) routes into MBGP, see the “Redistributing DVMRP Routes into MBGP” section. See the MBGP Network Advertisement Example section for MBGP network advertisement configuration examples.

Configuring Route Maps for MBGP Prefixes

To configure a route map for MBGP prefixes, use the following commands beginning in global configuration mode:

By default, neighbors that are defined using the neighbor remote-as command in router configuration mode exchange only unicast address prefixes. To exchange other address prefix types, such as multicast and VPNv4, neighbors must also be activated using the neighbor activate command in address family configuration mode, as shown.

Route maps that are applied in router configuration mode using the neighbor route-map command are applied to unicast address prefixes by default. Route maps for other address families, such as multicast, must be applied in address family configuration mode using the neighbor route-map command, as shown. The route maps are applied either as the inbound or outbound routing policy for neighbors under each address family. Configuring separate route maps under each address family simplifies managing complicated or different policies for each address family.

See the “MBGP Route Map Example” section for MBGP route map configuration examples.

Redistributing Prefixes into MBGP

Redistribution is the process of injecting prefixes from one routing protocol into another routing protocol. The tasks in this section explain how to inject prefixes from a routing protocol into MBGP. Specifically, prefixes that are redistributed into MBGP using the redistribute command are injected into the unicast database, the multicast database, or both.

To inject prefixes from a routing protocol into MBGP, use the following commands beginning in global configuration mode:

Route maps that are applied in router configuration mode using the redistribute route-map command are applied to unicast address prefixes by default. Route maps for other address families, such as multicast, must be applied in address family configuration mode using the redistribute route-map command, as shown.

See the “MBGP Route Redistribute Example” section for MBGP route redistribution configuration examples.

Configuring DVMRP Interoperability with MBGP

Cisco multicast routers using PIM can interoperate with non-Cisco multicast routers that use DVMRP.

PIM routers dynamically discover DVMRP multicast routers on attached networks. Once a DVMRP neighbor has been discovered, the router caches DVMRP routes that the neighbor sends. Those routes describe sources in a DVMRP cloud that want their packets to be received by receivers outside of this routing domain. MBGP allows the source prefixes of those sources to be known outside of the routing domain.

The router periodically sends DVMRP report messages advertising the unicast sources reachable in the PIM domain.

Redistributing MBGP Routes into DVMRP

By default, no MBGP routes are redistributed into DVMRP. However, you can configure all MBGP routes to be redistributed into DVMRP with a specified metric. Furthermore, to redistribute only certain MBGP routes into DVMRP, you can configure the metric and subject it to route map conditions. If you supply a route map, you can specify various match criteria options for the MBGP routes. If the route passes the route map, then the route is redistributed into DVMRP.

If there are multicast sources in other routing domains that are known via MBGP and there are receivers in a DVMRP cloud, they will want to receive packets from those sources. Therefore, you need to redistribute the MBGP prefix routes into DVMRP. This will be the scenario when distributing MBGP prefixes into the MBONE.

To redistribute MBGP routes into DVMRP, use the following command in interface configuration mode:

Redistributing DVMRP Routes into MBGP

If there are multicast sources in a DVMRP routing domain that need to reach receivers in MBGP routing domains, you need to redistribute DVMRP prefixes into MBGP. If you supply a route map, you can also use the set route-map configuration commands to specify various BGP attribute settings.

To redistribute DVMRP prefixes into MBGP, use the following command in address family configuration mode:

To redistribute DVMRP prefixes into MBGP, use the following command in router configuration mode:

See the “MBGP Route Redistribute Example” section for an example of redistributing DVMRP routers into an MBGP routing domain.

Configuring an MBGP Route Reflector

To configure a local router as a route reflector of MBGP prefixes, use the following commands beginning in global configuration mode:

By default, neighbors that are defined using the neighbor remote-as command in router configuration mode exchange only unicast address prefixes. To exchange other address prefix types, such as multicast and VPNv4, neighbors must also be activated using the neighbor activate command in address family configuration mode, as shown.

Route reflectors and clients (neighbors or internal BGP peer groups) that are defined in router configuration mode using the neighbor route-reflector-client command reflect unicast address prefixes to and from those clients by default. To reflect prefixes for other address families, such as multicast, define the reflectors and clients in address family configuration mode using the neighbor route-reflector-client command, as shown.

See the MBGP Route Reflector Example section for MBGP route reflector configuration examples.

Configuring Aggregate MBGP Addresses

The tasks in this section explain how to configure an aggregate address for MBGP. Specifically, the tasks in this section explain how to inject an aggregate address into the multicast database, the unicast database, or both.

To configure an aggregate address for MBGP, use the following commands beginning in global configuration mode:

Aggregate addresses that are defined in router configuration mode using the aggregate-address as-set command are injected into the unicast database by default. To enter an aggregate address in another database, such as the multicast database, the aggregate address must be defined in address family configuration mode using the aggregate-address as-set command, as shown.

See the Aggregate MBGP Address Example section for aggregate MBGP address configuration examples.

Verifying MBGP Configuration and Operation

To verify MBGP configuration and operation, perform the following steps:

MBGP Configuration Examples

MBGP Peer Example

Example 1: The following example shows how to use an address family to configure a neighbor as both unicast and multicast-capable:

MBGP Peer Group Example

Example 2: The following example shows how to use an address family to configure a peer group so that all members of the peer group are both unicast and multicast-capable.

The neighbor activate command is not required in this configuration because peer groups are activated automatically as peer group configuration parameters are applied.

MBGP Network Advertisement Example

The following examples show how to use an address family to inject a network number and mask into the unicast database and the multicast database:

MBGP Route Map Example

The following example shows how to use an address family to configure BGP so that any unicast and multicast routes from neighbor 10.1.1.1 are accepted if they match access list 1:

MBGP Route Redistribute Example

The following example shows how to use an address family to redistribute DVMRP routes that match access list 1 into the multicast database and the unicast database of the local router:

MBGP Route Reflector Example

The following example shows how to use an address family to configure internal BGP peer 10.1.1.1 as a route reflector client for both unicast and multicast prefixes:

Aggregate MBGP Address Example

The following example shows how to use an address family to configure an aggregate MBGP address entry in both the unicast database and the multicast database: