Exchanging C-Multicast Routes

Advertising C-Multicast Routes Using BGP

If the C-join received over a VPN interface is a source tree join (C-S, C-G), then the receiver PE router simply originates a Type 7 route (Step 7 in the following procedure). If the C-join is a shared tree join (C-*, C-G), then the receiver PE router needs to go through a few steps (Steps 1-7) before originating a Type 7 route.

Note that Router PE1 is the candidate RP that is conveniently located in the same router as the sender PE router. If the sender PE router and the PE router acting as (or MSDP peering with) the candidate RP are different, then the VPN multicast register messages first need to be delivered to the PE router acting as the candidate RP that is responsible for originating the Type 5 route. Routers referenced in this topic are shown in Understanding Next-Generation MVPN Network Topology.

1. A PE router that receives a (C-*, C-G) join message processes the message using normal C-PIM procedures and updates its C-PIM database accordingly.

   Enter the show pim join extensive instance vpna 224.1.1.1 command on Router PE3 to verify that Router PE3 creates the C-PIM database after receiving the (*, 224.1.1.1) C-join message from Router CE3:

2. The (C-*, C-G) entry in the C-PIM database triggers the generation of a Type 6 route that is then installed in the <routing-instance-name>.mvpn.0 table by C-PIM. The Type 6 route uses the candidate RP IP address as the source.

   Enter the show route table vpna.mvpn.0 detail | find 6:10.1.1.1 command on Router PE3 to verify that Router PE3 installs the following Type 6 route in the vpna.mvpn.0 table:

3. The route distinguisher and route target attached to the Type 6 route are learned from a route lookup in the <routing-instance-name>.inet.0 table for the IP address of the candidate RP.

   Enter the show route table vpna.inet.0 10.12.53.1 detail command on Router PE3 to verify that Router PE3 has the following entry for C-RP 10.12.53.1 in the vpna.inet.0 table:

4. After the VPN source starts transmitting data, the first PE router that becomes aware of the active source (either by receiving register messages or the MSDP source-active routes) installs a Type 5 route in its VRF mvpn table.

   Enter the show route table vpna.mvpn.0 detail | find 5:10.1.1.1 command on Router PE1 to verify that Router PE1 has installed the following entry in the vpna.mvpn.0 table and starts receiving C-PIM register messages from Router CE1:

5. Type 5 routes that are installed in the <routing-instance-name>.mvpn.0 table are picked up by BGP and advertised to remote PE routers.

   Enter the show route advertising-protocol bgp 10.1.1.3 detail table vpna.mvpn.0 | find 5: command on Router PE1 to verify that Router PE1 advertises the following Type 5 route to remote PE routers:

6. The receiver PE router that has both a Type 5 and Type 6 route for (C-*, C-G) is now ready to originate a Type 7 route.

   Enter the show route table vpna.mvpn.0 detail command on Router PE3 to verify that Router PE3 has the following Type 5, 6, and 7 routes in the vpna.mvpn.0 table.

   The Type 6 route is installed by C-PIM in Step 2. The Type 5 route is learned via BGP in Step 5. The Type 7 route is originated by the MVPN module in response to having both Type 5 and Type 6 routes for the same (C-*, C-G). The route target of the Type 7 route is the same as the route target of the Type 6 route because both routes (IP address of the candidate RP [10.12.53.1] and the address of the VPN multicast source [192.168.1.2]) are reachable via the same router [PE1]). Therefore, 10.12.53.1 and 192.168.1.2 carry the same route target import (10.1.1.1:64) community

7. The Type 7 route installed in the VRF MVPN table is picked up by BGP and advertised to remote PE routers.

   Enter the show route advertising-protocol bgp 10.1.1.1 detail table vpna.mvpn.0 | find 7:10.1.1.1 command on Router PE3 to verify that Router PE3 advertises the following Type 7 route:

8. If the C-join is a source tree join, then the Type 7 route is originated immediately (without waiting for a Type 5 route).

   Enter the show route table vpna.mvpn.0 detail | find 7:10.1.1.1 command on Router PE2 to verify that Router PE2 originates the following Type 7 route in response to receiving a (192.168.1.2, 232.1.1.1) C-join:

Receiving C-Multicast Routes

A sender PE router imports a Type 7 route if the route is carrying a route target that matches the locally originated route target import community. All Type 7 routes must pass the __vrf-mvpn-import-cmcast-<routing-instance-name>-internal__ policy in order to be installed in the <routing-instance-name>.mvpn.0 table.

When a sender PE router receives a Type 7 route via BGP, this route is installed in the <routing-instance-name>.mvpn.0 table. The BGP route is then translated back into a normal C-join inside the VRF table, and the C-join is installed in the local C-PIM database of the receiver PE router. A new C-join added to the C-PIM database triggers C-PIM to originate a Type 6 or Type 7 route. The C-PIM on the sender PE router creates its own version of the same Type 7 route received via BGP.

Use the show route table vpna.mvpn.0 detail | find 7:10.1.1.1 command to verify that Router PE1 contains the following entries for a Type 7 route in the vpna.mvpn.0 table corresponding to a (192.168.1.2, 224.1.1.1) join message. There are two entries; one entry is installed by PIM and the other entry is installed by BGP. This example also shows the Type 7 route corresponding to the (192.168.1.2, 232.1.1.1) join.

Remote C-joins (Type 7 routes learned via BGP translated back to normal C-joins) are installed in the VRF C-PIM database on the sender PE router and are processed based on regular C-PIM procedures. This process completes the end-to-end C-multicast routing exchange.

Use the show pim join extensive instance vpna command to verify that Router PE1 has installed the following entries in the C-PIM database: