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New Member

OSPF and "switchport block multicast"

Hello:

I have a series of 3550 switches between a core and edge router that are passing all traffic at Layer 2 (no Layer 3 services enabled on the 3550's). On each of the uplink ports between switches, we have "switchport block multicast" enabled because the network is being used for a lot of multicast traffic.

We are having difficulties forming OSPF adjacencies between the two routers, but IP traffic passes with no trouble. The devices are in their own VLAN across the switch. Thus, my question. Could it be that blocking unknown multicast is also filtering the OSPF LSA's riding on that VLAN?

Thanks,

Mike

2 REPLIES
New Member

Re: OSPF and "switchport block multicast"

I understand from this link that there is no distinction is being made from the LSA's multicast and other multicast, http://www.cisco.com/en/US/products/hw/switches/ps646/products_configuration_guide_chapter09186a008007e707.html

One option that you can try is to increase the multicast suppression threshold.

New Member

Re: OSPF and "switchport block multicast"

Hello,

you can use unicast vs multicast communication. But this will have some admin overhead.

int f0/0

ip ospf network non-broadcast

router ospf 1

neighbor 1.2.3.4

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