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rp in multicast pim-sparse mode

Posted on 2011-04-20
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Last Modified: 2012-05-11
Hello experts,

In my environment, the RP is statically assigned to each pim-enabled router and I am looking to change it to dynamically discover.
Regarding auto-rp in a pim-sparse environment, what do they mean by:

"When you configure an auto-RP router for PIM sparse mode, you must assign a static RP router to these two groups. You can then specify an RP mapping agent for other multicast groups."

I understand dynamic discover will take precedence over statically assigned. Does this mean I must leave the statically assigned RP on each router.
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Question by:trojan81
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6 Comments
 
LVL 17

Expert Comment

by:surbabu140977
ID: 35432319
No.

Auto-RP requires that you configure the RPs to announce their availability as RPs and mapping agents. The RPs use 224.0.1.39 to send their announcements. The RP mapping agent listens to the announced packets from the RPs, then sends RP-to-group mappings in a discovery message that is sent to 224.0.1.40. These discovery messages are used by the remaining routers for their RP-to-group map. You can use one RP that also serves as the mapping agent, or you can configure multiple RPs and multiple mapping agents for redundancy purposes

Source Router config
#####################
ip multicast-routing
 
ip pim send-rp-announce <interface> scope 16


ip pim send-rp-discovery

 scope 16

interface loopback0
ip address <address> <mask>
ip pim sparse-dense-mode
 
interface ethernet0
ip address <address> <mask>
ip pim sparse-dense-mode

interface serial0
ip address <address> <mask>
ip pim sparse-dense-mode
###########################

Client/receiver router config
######################
ip multicast-routing


interface ethernet0
ip address <address> <mask>
ip pim sparse-dense-mode

interface serial0
ip address <address> <mask>
ip pim sparse-dense-mode
############################

The above is extract from the below link. You can go through the below quick config guide for brief understanding.
http://www.cisco.com/en/US/tech/tk828/technologies_tech_note09186a0080094821.shtml

Best,
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Author Comment

by:trojan81
ID: 35434027
thanks, however it does not answer my question regarding initial static setup.

Here's another quote regarding auto-rp in a sparse environment:

"Of course, there's a chicken and egg problem there: how can you send out multicast information via multicast if the Auto-RP information is needed to make PIM-SM work in the first place?
The other choice with PIM-SM only interfaces is to configure static RP addresses for the Auto-RP multicast groups (the multicast groups used by Auto-RP itself to communicate). That way, the static info gets the Auto-RP multicasts distributed in sparse mode, and then the Auto-RP mapping information allows the other multicast groups to be joined.

http://www.netcraftsmen.net/resources/archived-articles/375-ip-multicast-and-pim-rendezvous-points.html

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Author Comment

by:trojan81
ID: 35435051
also, the reason I am doing this is to have multiple RPs. I will have two. Is it good practice to have those two RPs also be Mapping agents to each other? Would that work?

Do the two RPs have to be MSDP peers?
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LVL 17

Accepted Solution

by:
surbabu140977 earned 2000 total points
ID: 35440320
You have got this "chicken-egg issue" because you are using sparse mode. Sparse mode is totally pull technology and dense is push. That's why as a solution to this we have sparse-dense mode i.e if a RP is available (auto/static) it will use sparse else it use dense.

Autp-RP is cisco proprietory.
To Enable Auto RP you must specify an RP-Candidate and RP-Mapping
 
RP-Candidate is to announce your self as an RP, you can also announce one Router to be RP for certain groups and different Router to be RP for different groups.
 
RP-Mapping the Mapping agent can be the same Router as the Candidate but it also can be a different Router the mapping agent is telling all the routers in the Multicast Domain where is the RP for each group.
 
When you enable the RP Candidate you Join a Group 224.0.1.39 and all other routers in the multicast join Group 224.0.1.40 listening to the Mapping agent.

Following 3 lines will announce your RP
##################
ip pim autorp listener
ip pim send-rp-announce <IP>  scope 255 interval 10
ip pim send-rp-discovery <INTERFACE> scope 255 interval 10
###################

You can remove your static RP statement (ip pim rp-address) because you have already announced the RP using second line.

Best,
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LVL 17

Expert Comment

by:surbabu140977
ID: 35440350
btw, there is really not much admin overhead saving issue using auto RP or static RP. It's just a line difference. I generally leave it to sparse dense with static RP's. It's not like the dynamic routing vs static that it will save lot of admin overhead unless you are really into a very big multicast environment.

Best,
0
 

Author Comment

by:trojan81
ID: 35451917
It's a big environment and I dont want the chance mcast failing to dense mode if the RP goes down..i'd rather have mcast fail all together :).

my auto-rp is working in the test lab. I picked two switches to announce itself as RPs and mapping agents. When I take down 1 rp, the other (with lower IP) picks up as the rp.

I kept everything on sparse mode and issued the autorp listener command.
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