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Multicast works on some computers

Jeremy Phillips
Beginner
Beginner

Hi everybody.  Have a question that I need confirmation on. 

I have several schools that use programs for viewing what the students are doing on their computers.  The teacher can be at their desk and see what is on the students computer screen.  This program uses multicast to connect to each of the devices. 

If you can see about 75% of the screens is this a multicast routing or switching problem? 

They were working until a week ago, you could see all the screens no problem.  Would this be a software issue with the program instead?

Thanks for your help.

Message was edited by: Jeremy Phillips

1 Accepted Solution

Accepted Solutions

rsimoni
Cisco Employee
Cisco Employee

well, it depends if teacher and students are in the same subnet or not.

If they are no mcast routing is involved while if they are in different subnets you need a L3 device to route mcast. But since you say that the teacher can see some of the screens of the students, I SUPPOSE in the same classroom of the students she/he cannot see the screen of, I would rule out routing issue, even if mcast is actually routed.

Also, you should not necessarily focus on switching issue as it might very well be an application problem (sorry I am a network guy and I hate the "uhmm  this app is not working, there must be a network problem" approach ).

Beside that since IGMP snooping might play a role in how mcast traffic is forwarded a L2 level on switches, you might quickly disable it on your switches and see if that helps. Drawback is that ALL L2 ports in the given vlan where mcast traffic is present will receive mcast streams (flooding) instead of just the ones which have actual receivers connected.

Finaly, if this does not help, can you give us more details about how this application works (traffic flow info)

Riccardo

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9 Replies 9

rsimoni
Cisco Employee
Cisco Employee

well, it depends if teacher and students are in the same subnet or not.

If they are no mcast routing is involved while if they are in different subnets you need a L3 device to route mcast. But since you say that the teacher can see some of the screens of the students, I SUPPOSE in the same classroom of the students she/he cannot see the screen of, I would rule out routing issue, even if mcast is actually routed.

Also, you should not necessarily focus on switching issue as it might very well be an application problem (sorry I am a network guy and I hate the "uhmm  this app is not working, there must be a network problem" approach ).

Beside that since IGMP snooping might play a role in how mcast traffic is forwarded a L2 level on switches, you might quickly disable it on your switches and see if that helps. Drawback is that ALL L2 ports in the given vlan where mcast traffic is present will receive mcast streams (flooding) instead of just the ones which have actual receivers connected.

Finaly, if this does not help, can you give us more details about how this application works (traffic flow info)

Riccardo

Thank you very much for the reply.  That is what I was thinking also.  I am just the only one for the school district that looks after the network and just need to talk this over with those with more experience.

The desktop and wireless are in two different subnets.  But like I mentioned they use to work fine until last Thursday.  I talked to the hardware specialist here and he said when they reinstalled the program they were able to view that laptop.  Maybe an update got sent out last week.  I will have to ask about that.

But I did take the igmp snooping off the layer 2 switch connecting those where both those vlans are found and I do see traffic on that wireless vlan now.

I will look into it some more form a layer 2 view

if u need more help feel free to ask.

I attached a document to the original message.  This is showing the show ip mroute and debug ip mrouting.

The two vlans are 163 and 164 that the computers are suppose to be communicating with multicast.

Maybe you see something I don't.

Thanks.

can you point out which desktop could not be viewed and which one could just to do basic comparison?

ebarticel
Enthusiast
Enthusiast

I also suggest checking the logs of those PCs that are not seen by monitoring software. Maybe the firewall settings have been changed and blocks multicast.

Eugen

Thanks guys.  These ideas pointed us in the right direction.  I am going to get with our Hardware Specialist and review what is happening on those computers.

Thanks for your help.

Hi guys,

Thank you for the help.  As I thought some more about how this is routed from the wired vlan to the wireless vlan I was thinking about the different layer 2 and layer 3 commands for the multicast and realized that I forgot about the wireless access points are  layer 2.  I got onto them and removed the igmp snooping and now that program using the multicast is working.

Thanks for the help.

very good news

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