PIM DR

[rajeshk200_2]

Dudes

we have two routers providing 2 different feeds , if we have one DR, multicast groups on non-dr has not been forwarded to segment.

Can we have two pim DR elected on single LAN segment based on multicast groups?, If not pls advice any alternative to receive both feeds.

I tried blocking PIM neighbor on LAN,But it generates huge amount of hellos that brings down switches.

Many thanks

Rajesh

[Giuseppe Larosa]

Hello Rajesh,

there are two different roles/concepts:

PIM DR is elected per IP subnet

the PIM forwarder is chosen for each  (S,G) using PIM assert messages .

PIM assert messages are used to compare route to the source S including admin distance and metric.

There are then rules for breaking ties so the highest IP address on the subnet provides PIM DR election and may be PIM forwarder election.

IGMP querier is the lowest IP address on the subnet among multicast capable routers.

And this is a third role.

Depending on the unicast routing protocol in use you can influence PIM assert winner for a source S by making one device to have a better unicast route to S.

For example using a static route for S on device 2 it can win the PIM assert competition with device1.

So if the multicast streams have diffeerent source addresses you can try this way, if the source is the same you should accept that one router is the forwarder for both streams with the other one ready to take over.

>> I tried blocking PIM neighbor on LAN,But it generates huge amount of hellos that brings down switches.

not recommended

Hope to help

Giuseppe

[rajeshk200_2]

HI Giuseppe

Many thanks for the response.

Let me explain bit more, I have two routers each have different set of multicast groups and sources, By default only one DR elected

for all groups, So the scenario I have only half of groups getting forwared by DR(Router1) and non DR multicast groups geting dropped on router(Router2)

Ideally I need both the routers(router1 and 2) should be forwarding to LAN segment and obviously unique multicast groups and source.

Can this be achievd with your the solution ?

Regards

Rajesh

[Giuseppe Larosa]

Hello Rajesh,

the source addresses must be different and device 2 has to provide the best route to source2  in order to be chosen as the forwarder for (G2, S2) into the common LAN segment.

It is the same concept of RPF that applies to  the source address

if this happens you are fine.

Hope to help

Giuseppe

[rajeshk200_2]

Hello Giuseppe

I tried adding static route on Non-DR to influence the packet forwarding but no respite.

I can see packets being received on g 0/1 but not getting forwarded to g 0/0

The moment I change DR prioroty to higher number it's getting forwarded, but by this time other router stops sending packet on to g 0/0.

It's a standard setup where we receive two unique feeds from two leased circuits , I'm struggling to find the remedy but so far unsuccessful.

Many thanks

Rajesh

[hemantjohn]

Hi Rajesh,

I think you are confusing PIM DR and Multicast forwarder for a segment.

DR is tasked to relay the IGMP join messages from the segment to the RP, and to register a source to the RP.

Your requirement is to have different multicast "forwarders" on the same segment. This can be achieved if you have different sources of multicast streams. The order of choosing a forwarder of the multicast stream for a segment is:

1. The router with the lowest administrative distance to the source of the multicast stream will be the elected PIM forwarder.  This only happens if you are using two routing protocols or if you used  a static route pointing to the source.
2. If the AD is equal we will compare the unicast routing metric towards the source.
3. If the AD and metric are both the same we will elect the PIM forwarded based on the highest IP address.

Read more: http://networklessons.com/multicast/multicast-pim-assert-explained/#ixzz2efTBhxBv

I think Giuseppe is correct in suggesting manipulating the metric to the source to accomplish this.

thanks,

Hemant