mroute explanation - basics

Unanswered Question
Oct 2nd, 2009

Hi,

I'm seeing a lot of the following:

(10.44.50.35, 239.255.3.20), 2d03h/00:02:58, flags: PT

Incoming interface: Vlan50, RPF nbr 0.0.0.0

Outgoing interface list: Null

Can someone please help me to explain why my outgoing interface is set to "Null"?

Thanks

Dan

I have this problem too.
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Peter Paluch Fri, 10/02/2009 - 01:32

Hi Dan,

The Null in the oif list indicates that while your router is receiving a multicast stream from the 10.44.50.35 machine destined to the group 239.255.3.20, there are no directly connected receivers nor other multicast routers that wish to receive that stream from your router. In essence, this router does not know about any recipients, and as a result, it does not propagate the multicast traffic anywhere.

Do you expect this multicast stream to be forwarded? Do you have any recipients in your network that are subscribed to the multicast group 239.255.3.20?

Best regards,

Peter

dan_track Fri, 10/02/2009 - 01:48

Ohhh! Basically these are clients i.e (10.44.50.35) that want to receive a stream from a source.

I have two switches each with a separate connection to the site that has the stream of data on the multicast group 239.255.3.20.

On the other switch (both are 3750) it says the follwoing:

(10.45.8.35, 239.255.3.20), 13:19:32/00:02:59, flags: JT

Incoming interface: GigabitEthernet1/0/50, RPF nbr 10.10.51.106

Outgoing interface list:

Vlan50, Forward/Sparse, 13:19:32/00:02:17

Does this affect why this switch has it's outgoing set to Null on the other switch (switch2).

Thanks

Dan

Peter Paluch Fri, 10/02/2009 - 04:20

Hi Dan,

It would be helpful if you could provide us with a brief topology picture that would clarify how your network looks like. It is difficult to provide answers to your questions on a general base.

One thing, though. If you have a VLAN where the receivers are located that has multiple gateways (like two switches you have mentioned above), then only one of these gateways will be forwarding multicast streams onto this VLAN. Otherwise, a single multicast packet could be delivered multiple times which is not appropriate.

Do you have any actual issues regarding the multicast delivery in your network?

Best regards,

Peter

dan_track Fri, 10/02/2009 - 05:50

Hi,

I'll draw up a diagram. For now I'm not having any problem, I was just poking around and saw this on my other 3750 and wondered why it was different to my first 3750 in the same location. Both are joined via a trunk link.

Dan

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