Do we need Sparse-Dense mode in BSR Networks?

[turbo_engine26]

Hello,

I have a confusion point here and i wish somebody clear it up for me.

Because Auto-RP have this problem of "Chicken-and-Egg" in which (how PIM routers could join the 224.0.1.40 if they don't know the RP and how could they select an RP if they couldn't join that group), all interfaces must run sparse-dense mode. That's clear and fine with me.

However, in BSR networks, i think this mode is not needed anymore since BSR multicast its messages to all PIM routers (224.0.0.13).

Now, this mode did not only solve the "Chicken-and-Egg" problem in Auto-RP but also it introduced another benefit that will allow network admins to select which groups to operate in dense and which ones in sparse.

My questions are:

1- Do we really need to run sparse-dense in BSR networks as well?

2- If sparse mode is better than dense mode generally in terms of explicit joins and less overhead, Why selecting groups to operate in dense mode is called a "Benefit"? .. In other words, we need only 224.0.1.39 and 224.0.1.40 to operate in dense and other groups to be in sparse normally.

I'd really appreciate if someone volunteers and clear these doubts for me because i don't want to skip this during my study.

Thx

Regards,

AM

[Edison Ortiz · Accepted solution]

1- Do we really need to run sparse-dense in BSR networks as well?

No.

You don't need sparse-dense mode with Auto-RP.

You can configure auto-rp listener

http://www.cisco.com/en/US/docs/ios/ipmulti/command/reference/imc_04.html#wp1039806

2- If sparse mode is better than dense mode generally in terms of explicit joins and less overhead, Why selecting groups to operate in dense mode is called a "Benefit"? .. In other words, we need only 224.0.1.39 and 224.0.1.40 to operate in dense and other groups to be in sparse normally.

The benefit of having those groups running in dense mode is not requiring a RP to be configured for them to operate.

[Peter Paluch]

Hello Edison,

I apologize but I do not quite see why we are talking about Auto-RP with regard to BSR.

My understanding of the BSR is that it does not need any sparse-dense, autorp-listener or any of the stuff. Candidate RPs simply unicast their presence to the BSR router, and the resulting list of RPs is flooded through the multicast domain in a hop-by-hop fashion.

Best regards,

Peter

[Edison Ortiz]

Peter,

I'm clarifying this point he made:

"Because Auto-RP have this problem of "Chicken-and-Egg" in which (how PIM  routers could join the 224.0.1.40 if they don't know the RP and how  could they select an RP if they couldn't join that group), all  interfaces must run sparse-dense mode."

Interfaces don't need to run in sparse-dense mode for Auto-RP to operate. You can run Auto-RP + Sparse mode with AutoRP listener.

I already addressed the BSR question with a No.

[Peter Paluch]

Hello Edison,

Fair enough. I apologize if I intruded inappropriately. Thank you!

Best regards,

Peter

[Edison Ortiz]

Just a misunderstanding, don't go anywhere!

[turbo_engine26]

Peter,

You didn't intrude at all and you're always welcome.

I am actually the person who were talking about Auto-RP with regard to BSR since both mechanisms are for learning the RP address in the multicast network but with different processes. Sometimes the books' authors are not clear in certain areas in their explanations. For instance, book says: "sparse-dense mode should be the best practice when configuring multicast interfaces", and he stopped. This statement opened the gate for many doubts and i asked myself "What? ... Should i enable sparse-dense also as a best practice even with BSR?" .. Honestly, i've tried to look for the author's email but i couldn't find it because i have lots of questions. He should have cleared "When" and Which situations do i need to enable sparse-dense mode as a best practice (other than the Auto-RP situation). Therefore, i asked the question (and i actually know the answer) but i wanted to make more sure in a group discussion.

Regards,

AM

[turbo_engine26]

Thx Edison.

Fortunately, your answer has shown  me how much old the  book that i am using for my study even though it is  still recommended  by the CCIE society. The bad news is, Auto-RP  Listener isn't mentioned  at all in this book, i just knew it from you.  Also, this book (or any  book) recommends to run sparse-dense mode  always in the network.

1- Do we really need to run sparse-dense in BSR networks as well?
No.

I thought so, thx.

 2- If sparse mode is better than dense mode generally in terms of explicit joins and less overhead, Why selecting groups to operate in dense mode is called a "Benefit"? .. In other words, we need only 224.0.1.39 and 224.0.1.40 to operate in dense and other groups to be in sparse normally.
The benefit of having those groups running in dense mode is not requiring a RP to be configured for them to operate.

Great, but wait a min! isn't dense mode considered as an overhead mode in terms of flooding and re-flooding after prune state expires? 
Is it still a benefit? .. Why sparse mode came into light then? Besides, consider you run sparse mode in WAN and you make certain groups to operate 
in dense mode in this WAN, isn't it consuming the WAN resources?

(Remember: Sparse mode is stuitable for WANs and Dense mode is for LANs as per my studying experience)

But maybe i am wrong and hopefully you can clear my doubts.

BTW, the book is "Developing IP Multicast Networks". I find it an EXCELLENT book for learning the IP multicasting details.

Thx

Regards,

AM

[Edison Ortiz]

Yes, dense mode is not recommended for medium/large multicast networks.

If you read my reply, I said the benefit of having those groups running in dense mode.

I didn't say running dense mode is a benefit.

You should never run dense mode in a WAN/LAN as it will consume extra bandwidth resources

and you may run into scalability issues.

[turbo_engine26]

Hmmm.. okay thx