%OSPF-4-FLOOD_WAR - type-2 adv-rtr

Ran into a strange OSPF issue yesterday when moving a router off one core router and onto another.

Basically I moved a 10.1.0.1/30 link from a Cisco 6504 and onto a C9500.

The IP addressing stayed the same so on the 6504 it kept the /30 addressing but the interface went into a down/down state so I didn't bother removing the ip address itself from the interface in case I needed to revert back. It's down so I figured it would not be in the routing table or participating in OSPF.

I didn't notice at first as OSPF established fine on the 9500 and it's connected router but after about 20 minutes I noticed that other routers could no longer contact the 9500 through that /30.

When I checked the logs I could see lots of '%OSPF-4-FLOOD_WAR - type-2 adv-rtr' errors coming up on both the C9500 and C6504 for that /30 IP address I moved to the C9500.

As I had run out of my maintenance window I swapped it back so I could look into it further.

Now I'm wondering if this happened because the same /30 was left on the 6504 despite that interface no longer being up?

I didn't think it could/would make a difference but in the '%OSPF-4-FLOOD_WAR' message between the C9500 & C6504 it does mention that specific IP.

I'll be re-doing the work again but this time completing removing the IP address from the C6504.

I'm just sure however I've done this before without having to remove the IP itself if the interface went into a down state.