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Multicast in VXLAN Underlay

jlimbo987
Level 1
Level 1
 

Hi all, hoping for a bit of help from any multicast gurus out there.

 

I'm building the underlay network for a VXLAN setup and I can't get the multicast working properly. I'm using 4 nexus 9500v for the spines and 8 9300v for the leaves, both running v9.3.3 in GNS3

 

I've configured pim on all interfaces and have setup anycast rps with each spine available as an rp all having a loopback configured with the same rp address which is advertised into ospf. Each leaf has 4 routes to that IP so IGP routing is fine. 

 

The config on each spine is :-

 

ip pim rp-address 1.1.1.1 group-list 224.0.0.0/4
ip pim anycast-rp 1.1.1.1 1.0.0.1
ip pim anycast-rp 1.1.1.1 1.0.0.2
ip pim anycast-rp 1.1.1.1 1.0.0.3
ip pim anycast-rp 1.1.1.1 1.0.0.4

 

Each leaf switch has the following config:-

 

ip pim rp-address 1.1.1.1 group-list 224.0.0.0/4


As I understand it, when one rp gets a (s,g) it's supposed to register these with the other rps in the rp group so that when any of them receive a (*,g) they can tie the 2 together and start the flow from source to destinations. This doesn't seem to be happening. I have joined a loopback on a leaf to a mulicast group and then done a multicast ping from a loopback on another leaf. This fails.

 

When I check the mroutes on the spines, I find only one has the (*,g) and none have the (s,g). (s,g)s are only registered if the ping is sourced from the leaf interface connected to that spine and (*,g)s only appear on one random spine per multicast group.  The only way a multicast ping works is if it's sourced from the local interface on the leaf that is connected to the one spine that has the (*,g). That makes sense, but the point of the anycast config is that all the spines get (s,g) and (*,g) for a given stream. Also, why can't I get through from the loopback, which is what I'm going to need when it comes time to build the vxlan overlay on top

 

I've tried this on older 9ks and on titanium images, but the result is the same, so it doesn't look like a platform issue.

 

Any help is appreciated as always

 

Thanks

John

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