Hello Pinar
That’s a great observation. This is actually the result of an NX-OS internal mechanism that is applied by a process within the device known as the Adjacency Manager. That’s what the “am” at the end of that entry means.
AM routes are installed using a feature that creates a backup route when OSPF forms adjacency over a point-to-point link. This is not necessarily a point-to-point technology like a serial link, but a direct link between neighbors, even over an Ethernet connection, just like in your output.
It acts as a fallback mechanism if the OSPF-learned route is lost. It has an AD of 250, which is a very low preference. It is only better than “unknown,” which has a value of 255. It provides reachability to the neighbor’s router ID even if OSPF fails. It has the same exit interface as the OSPF route.
The AM route with AD 250 is a backup and won’t be used unless the OSPF route disappears. Note that in your output, the asterisk “*” is on the OSPF route, which is the currently chosen route. The other one acts as a standby backup, with a metric of 0. That 0 is actually just a place-holder, it has no meaning since AM is not really a routing protocol. The route itself is derived from the neighbor/ARP entry for that on-link IP, created by the Adjacency Manager to program the adjacency.
Why does this feature exist? Well, it provides additional resiliency. If you remove/lose the OSPF route, the AM route can become the active way to reach that specific neighbor IP (since it’s directly connected), but it won’t help you reach anything beyond it. It just keeps the adjacency up.
This behavior can be modified with the no ospf passive-interface command or by adjusting OSPF network types, but it’s generally beneficial to keep it for VXLAN underlay stability.
I hope this has been helpful!
Laz