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New Member

multicast problem in routers

hey guys
I have a problem with multicast, here is the senario.
I have a video Server that sends streams in multicast to its clients. the clients in same subnet with server don't have any problem and receives streams clear but the clients that are not in same subnet which means their packets must cross the routers  receive the streams so slow and not clear.
all of my routers are 3845 but my RP is 3945.
I changed all routers IOS but it doesn't fix the problem.
I enabled cef and MFIB on all router and on 3845 routers configurations are so simple, just setting  sparse-dense-mode and MFIB in interfaces and rp address for global.
so I will thank anybody who help me for rest of my life because I kinda thinking about killing myself because of this just doesn't make sense
thanks guys 

Everyone's tags (1)

I think you've posted this in

I think you've posted this in the wrong forum, but assuming the links between routers have enough bandwidth and aren't congested this sounds like you could have an MTU issue.

New Member

heythank you for the answer,


thank you for the answer, but please can you explain more about it....

the links between routers is ok because the same streams in unicast works well on them just when I send them multicast the problem comes up and it seems like i have a lot of packet loss or something

my software, I mean the app that sends the stream has a mtu field and i set it to 1500 should i change that?

Hi Amir - it would be worth

Hi Amir - it would be worth testing.  Try changing it to 1200 and see how you go.

It might be interesting to

It might be interesting to check on a wireshark trace what the device sends out and how the packets look like which are received.

(like if complete packets are missing, or only parts of a packet are received, ...)

There are multiple things that could happen. MTU could be one thing, but if its a local network with the standard mtu that might not be it.

The cpu load on the router could be to high, you might have some input threshold set, ...

If its a wireless lan you broadcast to, that might have its issues as well and multicast bandwidth might be limited by configuration as well, ....


Here is some multicast trouble shooting guide, maybe you get some more ideas there:


I also agree that this might be a question better asked and followed up in one of the router groups.

Please remember to rate helpful responses and identify

New Member

ok I check with wireshark, I

ok I check with wireshark, I receive a lot of multicast packets from my source the seem normal, but dont know if some of them drop or not

i just test something, I used that app which my source of multicast traffic in a lab environment and i had the same problem

multicast traffic i ok in layer 2 before they pass the router(I can see the stream clear) but when it pass the first router and it route the traffic the problem occurs(i can see the video stream but its slow motion) 

thank you for your help