Multicast over the WAN

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Oct 26th, 2009
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I have 2 devices on a spanned vlan on my WAN that require multicasting between them. Both devices are on the same vlan and connected to Cisco 6500 switch, but in different locations on my network. The switch has a L3 vlan configured for this interface, but with no PIM mode configured. The more I read about IGMP snooping as a possible solution, the more confused I become. Ideas anyone???

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Overall Rating: 3.5 (2 ratings)
lgijssel Mon, 10/26/2009 - 05:14
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As long as you have a layer2 vlan between the hosts, all multicast traffic will be received by default.

Multicast routing only applies when you are traversing layer 3 boundaries.



austin0824 Mon, 10/26/2009 - 08:31
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Thanks Leo.

I just tried it now, but multicasting worked with 2 devices within spanned vlan on same site.But when I tried it with devices on a different site on same vlan, it did not return any multicast.

Someone recommended I configure PIM Sparse-dense mode on the vlan interface. This seemed to work, but returned duplicate multicast for every unicast initiated. What do you reckon is wrong here?

Find below the output;

unicast from, seq=1093 dist=-1 time=0.000 ms

multicast from, seq=1093 dist=-1 time=0.000 ms

multicast from, seq=1093 dist=-1 time=0.000 ms (DUP!)



lgijssel Tue, 10/27/2009 - 07:36
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Within the same vlan, you should see all broad- and multicast traffic.

At least, that is the default behavior.

When you have configured anything with multicast, this behavior is altered and you will not get multicasts from non-standard sources like the range.


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