MSDP peer name resolution fails outside of GRT

[Philip DG]

We run MSDP across a mixture of IOS/XE 17.12 devices, both in GRT and in VRFs. These boxes all have name resolution enabled for NTP and other purposes.
We have noticed that executing "show ip msdp summary" on a device where MSDP is running in the GRT, displays the mesh peers and correctly resolves their IP addresses into FQDNs. However, on devices where MSDP is running in a VRF (and the GRT is empty of interfaces/routes/config etc), the name resolution does not take place even though those names are resolved correctly by a ping in the same vrf.

Troubleshooting this using debug domain and trying various VRF/GRT versions of the ip domain lookup, ip name-server commands  suggests that MSDP is only sending reverse lookups in the GRT. This is most strongly indicated by using the "ip host ..." command to manually add a peer record to the local host table in the GRT - "show msdp vrf XXX summary" immediately reflects that in the output, but not if the peer record is added instead to the local host table in the VRF.

Anybody else having the same problem? Am I missing something obvious or is it just a bug? MSDP itself is working fine otherwise.

[Giuseppe Larosa]

Hello @Philip DG ,

I think your understanding is correct .

MSDP is a routing protocol to be exchanged between RPs belonging to same or different BGP numbers.

With same AS --> Anycast RP with PIM SM or ASM (either with Cisco auto RP  or standard based BSR bootstrap protocol introduced with PIMv2)

within same AS no RP is required for PIM SSM but IGMPv3 is required

within same AS a phantom RP on a common L3 on core multilayer switches with PIM Bidirectional

Now coming to your question I would say that what you see is expected.

the same happens in IS-IS that uses CLNP packets over L2 (3 bytes are consumed by the greater encapsulation. without IP host command the show isis neighbors should show the net and not the hostame at least this happened in IOS.

What is your context ? are you introducing multicast support over Cisco Viptela SD WAN or you are just doing labs?

Hope to help

Giuseppe