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IGMP config - how to?

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Mutex
Occasional Advisor

IGMP config - how to?

Hello!

Can anyone explain how to configure my switches correctly to get IGMP working correctly in VLAN1? See attached picture.

Used equipment are two 2910al and two 2610al switches.

When I turn on IGMP in the webinterface for VLAN1 on every switch multicast traffic doesn't go through.

Do I have to configure the switches with the CLI? If yes can anyone show me how.

Thanks in advance Harald
16 REPLIES
Natasha Samoylenko
Trusted Contributor

Re: IGMP config - how to?

A Querier is required for proper IGMP operation. So you need IP address at least on one switch in VLAN 1.

In CLI you need to enable IGMP in VLAN 1 on every switch:
switch(config)# vlan 1 ip igmp

You can check if IGMP is enabled after you configured it in the webinterface or CLI:
show ip igmp config
show ip igmp

The source and client in common subnet, so you don't need any aditional steps.
Mohammed Faiz
Honored Contributor

Re: IGMP config - how to?

Hi,

It's easier to confirm that things are working as expected via the CLI, so what you can do is this:

on each switch -

switch# show ip igmp 1

That should tell you if IGMP is enabled on VLAN 1. If it isn't you need to run (on each switch)

switch# conf t
switch(config)# vlan 1 ip igmp

Then to determine whether your switches are seeing any multicast traffic run the first command again

switch# sh ip igmp 1

which should give you an output similar to:

VLAN ID : 1
VLAN Name : VLAN1
Querier Address : No Querier detected yet

Active Group Addresses Reports Queries Querier Access Port
---------------------- ------- ------- -------------------
224.0.1.60 280 0
224.0.1.127 12 0
Mutex
Occasional Advisor

Re: IGMP config - how to?

Hi!

Which switch should be the querier? Is there any rule?

And how do I set up an IP for that Switch in VLAN1.

Thanks for your Help!
Natasha Samoylenko
Trusted Contributor
Solution

Re: IGMP config - how to?

Generally it should work without querier, as I remember, but maybe this is the issue why it don't.
To configure IP in VLAN 1:
switch(config)# vlan 1 ip address x.x.x.x/xx

In your network topology this can be any switch.
Natasha Samoylenko
Trusted Contributor

Re: IGMP config - how to?

And also it is good to check if you can ping streaming server from streaming client.
Mutex
Occasional Advisor

Re: IGMP config - how to?

Hi!

Unicast traffic is no problem! Ping and everthing else like http work without problems. Only multicast makes problems in this configuration.
Just for Info: See attachemt -> Config of the first 2910 (where the streaming server is connected)
moreover: default_Vlan has id 1 and the VLAN1 of my schematic diagram is called Tripleplay and has id 3.
Natasha Samoylenko
Trusted Contributor

Re: IGMP config - how to?

I'm a little confused about VLAN 1 and VLAN 3 in your topology.

You have all devices in VLAN 3?
They all in general subnet? Is the streaming server and clients in general subnet?

If all devices in VLAN 3, then you need to configure IGMP in this VLAN.

From show command its looks like clients send IGMP report to server.
Mutex
Occasional Advisor

Re: IGMP config - how to?

Sorry for confusing! Now I have corrected the names and ids -> see attachment!

Yes I have my multicast Clients and the streaming Server in VLAN 3 (Tripleplay).
This devices are only in VLAN 3!

Here I have made a flickr set where I post my screenshots: http://www.flickr.com/photos/weillechner/sets/72157625017882781/with/5071547898/
Natasha Samoylenko
Trusted Contributor

Re: IGMP config - how to?

In your topology switches are connected with ports labeled as ports in VLAN 1.
May be this port also tagged in VLAN 3?
How streaming server and clients see each other?

You can also try to connect streaming client and server to the same switch. In this way you can test is this a switch to switch issue or may be some multicast streaming software issue.
Mutex
Occasional Advisor

Re: IGMP config - how to?

when I connect one client directly to the switch where the server is, then multicast works without problems.
When I switch the client back to the first switch SA004HP00_1 then suddenly the stream works on this switch too, but not on SA004HP00_2.

But when I power off all switches and restart them then streaming on SA004HP00_1 doesn't work again.

It seems that the switches have to learn something but after a restart they have lost this information and need to learn again.

By the way why does the switch loose the ip I set for VLAN 3 everytime I power off the switches?
Natasha Samoylenko
Trusted Contributor

Re: IGMP config - how to?

When multicast is enabled on switches they need to receive IGMP report from hosts to send multicast flow on ports.
After restart they once again must receive IGMP report from host.

Can you copy configurations of all your switches, at least part of config for VLANs 1 and 3?

"By the way why does the switch loose the ip I set for VLAN 3 everytime I power off the switches?"
You need to save your running configuration:
copy run start
Mutex
Occasional Advisor

Re: IGMP config - how to?

"Can you copy configurations of all your switches, at least part of config for VLANs 1 and 3?"
I will do that!

copy run start -> doesn't work!
Maybe there is another command, do you have any idea?
Natasha Samoylenko
Trusted Contributor

Re: IGMP config - how to?

Sorry :)
Instead of copy run start, use:
wr mem
Mutex
Occasional Advisor

Re: IGMP config - how to?

Thanks for your help! I found the command
write memory which is the long version of wr mem.

Moreover the problem is solved:

A querier was need in my topology. Therefore one Switch needs an IP address. -> see attachment.
After I have configured an IP address for one switch, the other switches register the configured switch as querier.

Thank you very much for your help!
Regards Mutex
Natasha Samoylenko
Trusted Contributor

Re: IGMP config - how to?

Glad to hear that your problem is solved.

I also read the docs and copy in my first answer information about querier. :)
But I also remember that in real life I did not face such a problem (I think this is because at least one switch always had an IP). So I was not quite sure about the querier.

For me it also good to recall that querier is always needed.
Pieter 't Hart
Honored Contributor

Re: IGMP config - how to?

It's the IGMP-snooping function that gets in your way.
This is to forward multicasts only to the subbscribed ports an NOT "flood" multicasts to all ports on the switch (all switches).

But there needs to be a DR (designated )router for the multicasts in the network for correct operation of IGMP(snooping).
It's not the switch that specificly need an ip-adress.

Without DR the switch that is NOT directly connected to the multicast source cannot determine what (uplink) port to subscribe to the multicasts.

By giving some switch an ip-address in the network, this takes the DR function and IGMP can forward the multicasts to the subscribed ports.

As such the switch closest to the multicast source seems the best candidate for the ip-adress.

A section from this document may clarify things: http://www.h3c.com/portal/Products___Solutions/Products/Switches/H3C_S5810_Series_Switches/White_Paper/200912/656291_57_0.htm

PIM-DM assumes that at least one multicast group member exists on each subnet of a network, and therefore multicast data is flooded to all nodes on the network. Then, branches without receivers downstream are pruned from the forwarding tree, leaving only those branches with receivers. This â flood and pruneâ process takes place periodically, that is, pruned branches resume multicast forwarding when the pruned state times out and then data is re-flooded down these branches, and then are pruned again.