Good IGMP tutorials 1

[baddos]

Anyone have any links to a good IGMP tutorial or a book for that matter. I'm running Catalyst and 3com switches with IGMP Snooping, but it still seams that the OSPF LSA's are still flooded to all ports on the switches.

 

[ADB100]

All link-local multicast traffic will ALWAYS flood within a VLAN. This is by design and you can't stop it unless you get into some hard-filtering. OSPF uses 224.0.0.5 & 224.0.0.6 (and also a TTL of 1) - these must be flooded for the protocol to work. Switches will ALWAYS forward these packets to all ports within a VLAN. Any Address that begins 224.0.x.x will always flood.

If you don't have any OSPF speakers on a VLAN (i.e. a User VLAN) then make the interface Passive.

Andy

 

[ADB100]

Sorry not 224.0.x.x, but 224.0.0.x and 224.0.1.x.

Reasonable page here

http://www.firewall.cx/multicast-intro.php

But try CCO

Andy

 

[baddos]

Can't you disable that on a per port basis? Like obviously, I want my trunk ports and router ports to flood multicast traffic. But host pcs on the vlan running ospf shouldn't need that. I already run passive interfaces on the vlan's that I know are only hosts, but not on my main vlan (for obvious reasons ).

I guess I could create a separate VLAN for my OSPF routers, but it seems like a waiste.

 

[ADB100]

No, as I said you could set up some custom filters and apply them to Workstation/Server ports and not to Router ports, but thats it.

Why have you got PC's on a VLAN where OSPF is anyway? In a typical design you won't have PCs/Servers on a VLAN where routed traffic needs to traverse - these should be 'backbone' links and router-to-router links. User traffic should generally be 'stub' type networks where OSPF should be 'passified'.

Andy

 

[baddos]

It's my server VLAN. It does routing, servers, and network printers. The users are on their own vlans with passive interfaces.

 

[ADB100]

Create another VLAN?

Andy