OSPF same subnet different areas

[Luis Seyler]

Hi!

I have an OSPF process with several areas, in two areas different than 0 I have the same subnet, this was done because it some sort of requirement to put production vlans outside area 0, but that subnet (and some others) communicate through L2 and are separated physically by a DCI. The solution is working but I'm getting some OSPF logs and would like to stop those logs from showing.... or maybe a better solution? this was done using nx-os

Thanks!

[dbeattie]

Hi Luis,

If I understand your question correctly, you have two segments that make up one sub-net. The segments exist either side of a DCI link. If these are access segments (i.e. not used for transit) and the DCI link is just used to allow servers in each segment to run sync/heartbeat (not unusual), you should be able to set all of the SVIs in the subnet to being OSPF Passive. This will prevent the switches from trying to peer with each other and will stop the logs happening. Obviously, this will not help if you actually need the switches to peer on this sub-net.

Hope this helps,

Dave

[Luis Seyler]

Thanks! don't know how I forgot about that, just wondering here... If I do that and I have a cost associated with that SVI, would it affect the cost that I assigned to it? I think it shouldn't but not 100% sure, just in summary it would be something like this

MLS1

interface vlan 10

 ip address 192.168.10.1/24

 ip ospf cost 1

router ospf 1

 network 192.168.10.1 0.0.0.0 area 10

 passive-interface vlan 10

MLS2

interface vlan 20

 ip add 192.168.10.2/24

 ip ospf cost 10

router ospf 1

 network 192.168.10.2 0.0.0.0 area 20

 passive-interface vlan 20

assuming an L2 interconnection, the core, area 0, would know subnet 192.168.10.0/24 through MLS1 with a cost of 1, is that right?