Multicast on a cisco 4506

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May 2nd, 2008
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My server admin hasn't used Norton Ghost in awhile and he went to use it the other day and it didn't work. I asked him try pushing it out by unicast and it worked. I enable IP Multicast-routing on my core switch but it still doesn't seem to be working. I know there are tons of pages of documentation out there, but i was wondering if anyone had any suggestions. It seems like by enabling that IP Multicast-routing the core switch should be able to just forward it out to the appropriate vlan.

Correct Answer by cisco_lad2004 about 9 years 1 month ago

800, u might be better off using pim dense mode then.


anyways, for RP "ip pim rp-address x.x.x.x" x.x.x.x is a loopback for example.

ur RP should be located close to the source. it will set the source of multicast forwarding tree.


also, if the application needs a good uptime, redundant RP is best.


I still think with 800 trees, dense mode is best and no RP is needed.


to be sure it work, do "so ip mroute count" u will see if packets are forwarded.


HTH


Sam

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cisco_lad2004 Fri, 05/02/2008 - 06:56
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u also need to enable PIM on the interfaces that u wish to use for multicast forwarding.

if u do not have many devices, I suggest you use pim sparse mode and static RP. this is basically all what u need for a simple set up.


HTH


Sam

cowetacoit Fri, 05/02/2008 - 07:04
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Thanks Sam. I have enabled IP MULTICAST-ROUTING, I enables IP PIM SPARSE-MODE on the vlans i want it to run on. As far as the RP, i just randomly choose a class d address? I have about 800 devices on our network. My 4506 does the intervlan routing with about 30 vlans. I did everything but set a RP and i htink it is working now. How do i set a static RP?

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cisco_lad2004 Fri, 05/02/2008 - 07:15
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800, u might be better off using pim dense mode then.


anyways, for RP "ip pim rp-address x.x.x.x" x.x.x.x is a loopback for example.

ur RP should be located close to the source. it will set the source of multicast forwarding tree.


also, if the application needs a good uptime, redundant RP is best.


I still think with 800 trees, dense mode is best and no RP is needed.


to be sure it work, do "so ip mroute count" u will see if packets are forwarded.


HTH


Sam

cowetacoit Fri, 05/02/2008 - 08:42
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ok Sam. It seems to be working now. I have IP Multicast-routing enabled, IP PIM Dense-Mode running on vlans i need multicast.

Harold Ritter Sat, 05/03/2008 - 06:56
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Samir,


There is 800 devices in the network doesn't necessarily mean that the multicast traffic is needed everywhere. Running dense mode could have negative effect if the multicast traffic is not required everywehere.


Very few networks are still running dense mode. Dense mode is more efficient at the control plane level as it leads to less state information but this is significant only if you have lots of source and groups. On the other hand, it is very inefficient as it will flood the mcast streams everywhere in the network, even where it is not required, and this every 3 minutes by default.


Rgards,

cowetacoit Sat, 05/03/2008 - 07:08
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my show ip mroute routing table is HUGE! I have pim dense running on 4 vlans. it's working but the application i know that needs it right now it Norton Ghost. Any reason the routing table is so big? Lots of different multicast addresses. Seems like all of my hosts should be responding to one multicast address. maybe i need to go back and read some more.

cisco_lad2004 Sat, 05/03/2008 - 07:45
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unless you have other applications sourcing multicast. there should not be that many groups.


I suggest you start by identifying which multicast addresses are sourced from where.


look at the ip mroute, and if u have (S,G) you can trace the source to validate.

once you have all addresses you need, it will be simpler troubleshoot and eliminate unnecessary streams.


HTH


Sam

cisco_lad2004 Sat, 05/03/2008 - 07:40
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Harold,


As per initial posts, I suggested sparse mode. however, based on the assumption that all 800 are requesting multicast I went on to recommend dense mode.

of course I agree with using sparse as much as possible. and if I may add even stop switchover from RPT to SPT.


Sam

Harold Ritter Sat, 05/03/2008 - 08:36
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Samir,


It is always dangerous to assume ;-) I agree with your latest recommendation.


Regards,

Harold Ritter Sat, 05/03/2008 - 08:35
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Just as a correction. PIM dense mode will always build a source tree, which means more state information than sparse mode RPT. Consider that a momentary lapse of reason ;-)


Regards,

cowetacoit Mon, 05/05/2008 - 04:48
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I removed dense-mode and configured sparse-mode. The only thing i have done is enabled IP PIM SPARE-MODE on about 4 vlans and like i said my routing table is huge. Hoe do i track down Norton Ghost multicast address and only allow that IP to run?

cisco_lad2004 Mon, 05/05/2008 - 05:13
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To be 100% sure , u need to find out from the application itself which group it is streaming.


At the end of the day, if dont desire any other Multicast, identify the sources and stop them from streaming.


Sam

cowetacoit Mon, 05/05/2008 - 06:38
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I'm also seeing a multicast address that a bunch of hosts are talking to, i did a tracert to the 2 multicast addresses and they came back as our proximity panels. Why would random hosts be talking with them through mcast?

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