Friday, June 3, 2011

Multicast for MPLS VPN Extranet

In my earlier blog post, I've mentioned briefly about Multicast VPN across MPLS VPN. In this setup, the VRF must share the same default Multicast Distribution Tree (MDT), in this example, for the multicast VPN to form dynamically. Consider the following setup:

The source server (on PE1) is streaming on multicast mode. The VRF-Green, on the other side of PE2, would be able to join to the same multicast distribution tree ( and recieve the multicast stream. For this Intranet Multicast VPN to work, the VRF-Green on both PE routers should share the basic common configuration as follows:

Router PE1 and PE2
  ip vrf VRF-Green
  mdt default
  route-target export 65001:100
  route-target import 65001:100
ip multicast-routing
ip multicast-routing vrf VRF-Green
ip pim rp-address
ip pim vrf VRF-Green rp-address
router bgp 55
  address-family ipv4 mdt
    neighbor x.x.x.x activate
    neighbor x.x.x.x send-community extended
  address-family vpnv4
     neighbor x.x.x.x activate
     neighbor x.x.x.x send-community extended

However, the VRF-Blue (on PE2) won't be able to join the same MDT, as Cisco routers do not support multiple duplicate default MDT across VRFs. However, there is a workaround for this Extranet setup. Do note that data flow in MPLS VPN happens in label-exchange. Create another VRF-Green on the source PE1 and import the multicast traffic over to VRF-Blue on PE2. There are 2 options of importing, either import it on the source PE or on the reciever PE. I observed that the latter reciever PE option is more reliable if there are more than 1 reciever PE routers.

Configuring the Receiver MVRF on the Source PE (Option 1)
On PE1, add "route-target import 65001:100" on VRF-Blue, enable multicast routing "ip multicast-routing vrf VRF-Blue", and specify the same Rendezvous Point (RP) as VRF-Green for VRF-Blue using "ip pim vrf VRF-Blue rp-address".
For this setup, assign a new default MDT group for VRF-Blue on both PE routers ( in this example). Import the label on VRF-Green over (route-target import 65001:100) as shown in above diagram. In this way, two multicast distribution trees (MDTs) can be created from the same source server. When you perform a "show ip mroute vrf VRF-Green" on PE1, you'll see Extranet receivers in VRF-Blue.

Configuring the Source MVRF on the Receiver PE (Option 2)
Another option is to do the import on the reciever PE (PE 2 in this example). As mentioned earlier, I observed that the stream is slightly more stable if there is more than 1 reciever PE. You'll need to do the import on every reciever PE.
Ensure RPF and multicast routing is sound for GRT level on all PE and P routers, as well as VRF level for all PE. In this example (some outputs truncated):
GRT level
#sh ip mroute
(,, 00:54:29/00:02:12, flags: TA
  Incoming interface: Port-channel1, RPF nbr
  Outgoing interface list:
    Port-channel2, Forward/Sparse, 00:54:29/00:03:15

VRF level
#sh ip mroute vrf VRF-Green
(,, 00:54:29/00:02:12, flags: TA
  Incoming interface: Tunnel1, RPF nbr
  Outgoing interface list:
    VLAN123, Forward/Sparse, 00:54:29/00:03:15

For further details, refer to the Cisco Multicast VPN Extranet support.

Multipath with Redundant Routers
If you have redundant paths with some load splitting or sharing, you may have to consider enabling multipath options using following steps on every router:

  1. enable
  2. configure terminal
  3. ip multicast multipath s-g-hash next-hop-based
  4. ip multicast vrf vrf-Name multipath s-g-hash next-hop-based
  5. end
  6. show ip rpf source-address group-address
  7. show ip route ip-address


  1. Thanks. Literally the only Extranet "working" solution on the Internet.

  2. It should be noted that for Option 2 the RP must be local to PE2. It can be in either VRF, but it can't be learned via MPLS (from PE2's point of view).