Redistribution

Redistribution is the process of importing routes from one routing protocol to another. When routes are redistributed into BGP using the redistribute command, you have to specify the BGP table (Adj-RIB-In, as specified in BGP) into which the routes are to be imported. This BGP table can be either the unicast BGP table or the multicast BGP table.

Old Style

The old style of specifying the table into which a route had to go used the set nlri clause in the redistribution route map. The set nlri clause in the redistribution route map has the following semantics:

• set nlri multicast— Redistributes the matching prefix to the multicast table.

• set nlri unicast multicast— Redistributes the matching prefix to both unicast and multicast tables.

• set nlri unicast— Redistributes the matching prefix to the unicast table only.

• set nlri— Unspecified results in unicast behavior only.

The following example demonstrates redistribution into BGP so that all "connected" prefixes matching access list 1 in the routing table are imported as multicast NLRI:

router bgp 109
  redistribute connected route-map mbgp-source-map
  !
route-map mbgp-source-map
  match ip address 1
  set nlri multicast

AF Style

With the introduction of AF mode, the AF under which the redistribute command is specified determines the table into which the redistributed prefixes are injected. For example, if the redistribute statement resides under address-family ipv4 multicast mode, the redistributed prefixes are injected as multicast IPv4 NLRI. Hence, the preceding old-style redistribution configuration translates into the following in AF style:

router bgp 109
  !
  address-family ipv4 multicast
  redistribute connected route-map mbgp-source-map
  !
route-map mbgp-source-map
  match ip address 1

Note that with the introduction of the redistribute statement within AF mode, the clause set nlri is not required, and the parser would reject the presence of set nlri in the route map paragraph.