Multicast Bidirectional PIM

Lessons Discussion
41

Hello Muhammad

Yes, you are correct. I will let @ReneMolenaar know to make the necessary modifications.

Thanks!

Laz

42

Hi,
Can someone please explain the difference between designated forwarder (which is used in bidir) and designated router (used in sparse mode)?

43

Hello Nipun

The designated router is the router that will forward the PIM join message from the receiver to the RP.

The designated forwarder in BDIR is the router that will forward multicast traffic to the RP.

Notice that the designated router forwards control messages (PIM join) while the designated forward forwards actually multicast (user) traffic. Another way to say it is that the designated router functions on the control plane while the designated forwarder operates on the user plane.

For a more detailed explanation of the designated router and its function, take a look at this lesson:

I hope this has been helpful!

Laz

1 Like
44

Really helpful @lagapidis Thanks a lot.
I have another question.
How to configure PIM Bidir in bsr mode? I couldn’t add the bidr keyword in bsr commands.

45

Hello Nipun

In the Cisco IOS implementation of PIM, each multicast group individually operates in one of the following modes: dense mode, sparse mode, or bidirectional mode. Groups in sparse mode (PIM-SM) or bidirectional mode (bidir-PIM) use RPs to connect sources and receivers. All routers in a PIM domain need to have a consistent configuration for the mode and RP addresses of the multicast groups.

The Cisco IOS software learns the mode and RP addresses of multicast groups through the following three mechanisms: static group-to-RP mapping configurations, Auto-RP, and bootstrap router (BSR). By default, groups will operate in dense mode. No commands explicitly define groups to operate in dense mode.

The above is taken from this Cisco command reference for the ip pim rp-addresscommand.

Therefore, BSR should be capable of informing neighboring routers of the BIDIR mode when using BSR.

In the lesson, the RP was defined statically, and the bidir keyword was available. I went into the lab to check this out fpr BSR, and found that I had the bidir keyword available. Specifically:

R1(config)#ip pim rp-candidate gigabitEthernet 0/0 ?
  bidir       Group range treated in bidirectional shared-tree mode
  group-list  group-list
  interval    RP candidate advertisement interval
  priority    RP candidate priority
  <cr>        <cr>

The rp-candidate keyword is that used to indicate that BSR is employed.

Similarly, if you were to employ AutoRP, you have the bidir option available too.

R1(config)#ip pim send-rp-announce gigabitEthernet 0/0 scope 10 ?
  bidir       Group range treated in bidirectional shared-tree mode
  group-list  Group access-list
  interval    RP announcement interval
  <cr>        <cr>

Keep in mind that the bidir keyword is only available if BIDIR-PIM is enabled using the global ip pim bidir-enable command.

I hope this has been helpful!

Laz

46

Thanks.this helps @lagapidis

1 Like