I have physical ethernet link between a ASR-1001-X and a N3K (3048-TP). When I enabled OSPF on the interface and brought the interface up, everything looked find and dandy. Interfaces show up/up. I could see CDP. I got my neighborship going via OSPF . I was learning the routes as expected from both sides.
However, ping is failing between the N3K and the ASR-1001-X. I tried pinging from the N3k to the ASR (other side of the /31 interface) and the ping failed. Ping / all standard traffic was failing even though I learned of routes via OSPF. For some reason the N3k and the ASR were isolated, but still could form a OSPF neighbor-ship. As I was troublehsooting this, I decided to take one command off at a time on the interface level to see if it would fix it. After removing the medium p2p on the ASR end, communication was restored.
Since the devices are being staged and not actually moving traffic, I decided to troubleshoot what the behavior is like. I put the medium p2p command back on the interface of ASR. I do a packet capture on the ASR and from it's perspective, it is receiving OSPF hellos (as well as sending out OSPF hellos) @ 224.0.0.5. Ping is being received from the N3K, and responded. For some reason though, I am still timing out pings on the N3k. (and vice versa if i try send a ping on the ASR end). I then tried removing P2P on the N3K, and leaving it still on ASR. Still fails. I take off medium p2p on the ASR and wa-la it works just fine. I have no idea what is happening on the wire but this medium p2p command on ASR is just bad.
From OSPFs perspective, the links are seen as p2p with or without the medium p2p command present. OSPF communication works just fine. But everything else does not between each other when medium p2p is configured. It is my understanding this command is suppose to force OSPF to view it as a p2p link. Instead, it is breaking communication.
As a final note, The ASR is also directly connected via ethernet to same model ASR. Both sides of interface (ASR-1 and ASR-2) have the medium p2p command configured. And communication works fine between those two ASRs. But whenever it is enabled when interconnected with the N3K, it just straight up breaks.
interface config:
ASR Config:
interface GigabitEthernet0/0/1
xx.xx.xx.xx/31
no ip redirects
no ip proxy-arp
medium p2p
ip ospf network point-to-point
ip ospf xxxx area 0.0.0.0
negotiation auto
cdp enable
N3K Config:
interface Ethernet1/37
xx.xx.xx.xx/31
no switchport
medium p2p
no ip redirects
ip ospf network point-to-point
no ip ospf passive-interface
ip router ospf xxxx area 0.0.0.0
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