Ghostcast slow on some clients
I am trying to do a GhostCast using Multicast to several clients (using GhostCast Server 11.5.0.2113). I used to be able to do so to any of the clients on my network with speeds around 550 MB/min. Now, however, I am getting speeds closer to 60 MB/min! I have noticed that of the four clients I have been using to troubleshoot this, two of them are on an older Cisco switch (3500XL series), and the other two are on a newer switch (Cisco 3750 series). I have also noticed that if I GhostCast to just the two on the newer switch, I get a decent rate; but if I include the ones on the older switch I get the slower rate.
I have seen all the forum discussions about IGMP affecting this, however my network setup is extremely simple: all my switches are just joined together with no routers on the network. I did make sure IGMP was disabled on the newer switch, and CGMP is disabled on the older switch (which doesn't support IGMP). I don't know what would have changed on my network that would cause this to suddenly stop working (it worked as of about a week ago).
Perhaps another helpful piece of information: I turned on debugging in the GhostCast Server, and I noticed at the end of the session there was an extremely high number of "Retransmits on Timeout". On the session that was fast, I only had 3669; on the slow session there were 488,635.
I realize this is probably something configured wrong in my network, but I am appealing to the group knowledge of networking (since my knowledge is very limited). Does anyone have any ideas of what to try? I'm flat out of ideas.
Thank you,
Keith
Comments
Re-enable IGMP and CGMP
Hi,
First of all, you are mentioning that you have disabled the CGMP protocol on the older switch and IGMP on the newer switch. CGMP (IGMP snooping protocol) and IGMP are the Cisco protocols used to handle multicast traffic. In your situation, Ghost Cast is trying to multicast the information and expects your clients to join a multicast group before starting the image transfer. As none of your switch is set to handle multicast groups, your server will retransmit its request. In the meantime your clients will try to download the image in unicast. You speed/rate is therefore affected.
I would suggest you re-enable those two protocols. Then you can connect your clients to the switch you like taking into consideration the two following points:
- On your newer switch IGMP will manage the multicasting groups. Note: make sure your switch support IGMP v3
- On your older switch CGMP optimize the multicast redirecting it.
PS:
- IGMP is a layer 3 protocol and can only be enabled on Layer 3 switches. IGMP protocol aims at saving bandwidth as a single communication channel is opened to several clients.
- CGMP or IGMP Snooping is a Layer 2 protocol with limited Layer 3 capabilities to listen to IGMP requests. CGMP will listen to the multicast requests and redirect the `Multicast traffic to the proper ports to avoid flooding the network.
Hope it helps
Got it working somehow
Thanks for the suggestions. The reason I'd disabled them is that I was under the impression that IGMP would not work without a router to send out the group requests. Of course, my networking knowledge is very limited, so I'll defer to your advice. Unfortunately, I will not be able to try it out until next month, as we are just entering a release testing phase. I don't think they'd appreciate me messing with the network just before some heavy testing.
Fortunately, I managed to get the GhostCasts working before the holidays. I'm not sure what fixed it, but I have my suspicions. Here are some of the things I tried:
I suspect fixing #3 is what cleaned up the network. Since it's been longer than a week, I can't remember for sure, but I think I tried it after the first two changes and still had the issue.
I'll have to play with it some more in February.
Thanks again,
Keith
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