I've never really heard of the behavior being called "split-horizon" in the multicast context so I Googled around about it. I see it unofficially referred to in that manner by blogs and a quote from Doyle, vol II, but I believe it is actually part of the overall RPF-based loop prevention feature which prevents the receiving interface (which would be the RPF interface) from being added to the OIL.
Frankly if Michael is prepping for lab as opposed to written, understanding the feature operation and when to deploy it is more important than semantics of the best name to call it. Do you have a reference for your recommendation to reload the router after enabling? I've never had to do that. Good point about dense mode. A place that can be confusing is AutoRP, which relies on dense-style flooding. AutoRP does not work with PIM NBMA. Best Regards, Bob On Thursday, March 21, 2013, Imran Ali wrote: > pim nbma has nothing to do with RPF . > > only three parameters matters to RPF , igp unicast table , MBGP , > mroutes. > > " pim nbma " is used for disable split horizon , similar to any distance > vector split horizon rule. > > By default a router includes the interface S 0/0 in OIL , after enabling > pim nbma it inclued based on neighbors ip's on that interface. you will > see after S0/0 , an ip address of remote dlci appear in oil . > > After enabling nbma , i always reload the router router :-) . > > The only thing to worry about here is spoke should not become ASSERT > winner on a hub and spoke topology , as now hub prunes back and > remaining spokes which are only connected to hub will not get the feed. > > further " pim nbma " does not work with dense mode... > > > On Thu, Mar 21, 2013 at 8:02 AM, Bob McCouch > <[email protected]<javascript:_e({}, 'cvml', '[email protected]');> > > wrote: > >> Hey Michael, >> >> I'm pretty certain you won't get a PIM adjacency up over a frame PVC that >> does not have pseudo-broadcast enabled. PIM uses 224.0.0.13 for neighbor >> discovery. And the multicast packets that PIM is routing most definitely >> need a broadcast-enabled frame PVC. >> >> The 'ip pim nbma-mode' is not related to whether PIM uses link-local >> multicast for neighbor discovery, rather it is used to deal with potential >> RPF issues in a frame-relay hub and spoke network. If the hub receives a >> multicast packet from a spoke off of the frame-relay link on Serial1/0, >> for >> example, it would not be able to forward that same packet back out to >> another spoke neighbor off the same interface as the interface the packet >> was received on (the RPF interface) cannot be included in the OIL for the >> group (as that would indicate an automatic RPF violation). >> >> 'ip pim nbma-mode' simply allows the router to include the actual PIM >> neighbor ID rather than the interface in the OIL so that the router can >> "hairpin" the multicast packet and send it back out to spokes other than >> the one it was received by. >> >> Can you get PIM and multicast across a non-broadcast frame-relay link? >> Sure >> -- that's what tunnels are for ;-) >> >> Good luck on your lab! >> >> >> On Thu, Mar 21, 2013 at 12:03 AM, Michael Davis - Webquor < >> [email protected] <javascript:_e({}, 'cvml', >> '[email protected]');>> wrote: >> >> > Hi everyone – I am working on multicast which is my biggest weakness >> > leading up to the lab next week. I am trying to get a PIM adjacency >> over a >> > non broadcast frame-relay connection. It is not coming up. Can someone >> > please explain if it is possible and why the command "ip pim nbma-mode" >> is >> > necessary on non-broadcast networks? The command doesn't seem to do >> > anything to be honest. I suppose the big question is can I establish a >> PIM >> > adjacency over a frame-relay connection where no broadcast capability is >> > enabled? >> > >> > _______________________________________________ >> > For more information regarding industry leading CCIE Lab training, >> please >> > visit www.ipexpert.com >> > >> > Are you a CCNP or CCIE and looking for a job? Check out >> > www.PlatinumPlacement.com >> > >> > http://onlinestudylist.com/mailman/listinfo/ccie_rs >> > >> _______________________________________________ >> For more information regarding industry leading CCIE Lab training, please >> visit www.ipexpert.com >> >> Are you a CCNP or CCIE and looking for a job? Check out >> www.PlatinumPlacement.com >> >> http://onlinestudylist.com/mailman/listinfo/ccie_rs >> > > _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com http://onlinestudylist.com/mailman/listinfo/ccie_rs
