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show ip mroute detail: inactive flow

MATTHIAS SCHAERER
Level 3
Level 3

‎04-12-2023 04:05 AM

In "show ip mroute detail" on a Nexus 9k (let's call it N1) a S,G entry shows a flow that is described as "inactive". The entry is based on a static IGMP join that I have configured on a Loopback interface. On a neighbouring router (let's call it N2) the same flow is "active", also static join with Loopback, the counters show that traffic is being received and also sent out over the interface to N1 and to the local Loopback.
In N1's routing table the path to the multicast source is present, so I assume that the RPF check should succeed. N1 has an established PIM neighborship to N2, N2 vice versa and another neighborship towards the router behind which the multicast source is located.
The whole setup is PIM sparse mode, MSDP is in play but seems to work at least for N2. What needs to happen that N1 also shows an active flow and receives the multicast stream that N2 happily receives?

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MATTHIAS SCHAERER
Level 3
Level 3

‎04-14-2023 04:34 AM

Interesting detail to add:

when removing the static ip igmp join on N2, the flow on N1 gets active immediately and I can see packet/byte counters increase with "show ip mroute detail"

So the question is:
-Is N2 not forwarding the Mcast traffic out to N1 event though the interface is in the outgoing interface list of "show ip mroute"?

I found  a document for the Nexus 3548 that states something like that under https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus3548/sw/93x/multicast/b-cisco-nexus-3548_switch-nx-os-multicast-routing-configuration-guide-93x/b-cisco-nexus-3548_switch-nx-os-multicast-routing-configuration-guide-93x_chapter_011.html#.... I did not yet find a similar document for the Nexus 9000, however configuring "ip igmp static-oif" instead of "ip igmp join-group" results in having increasing counters on both Nexus devices. So it somewhat explains how it works. If someone knows why it works that way, this might be interesting.