OSPF Passive Interfaces

[Mokhalil82]

Hi

I am just trying to verify if I am right about the passive interface in ospf. If I have 2 x Layer 3 switches connected to each other (Core A and Core B) via a routed link. Both switches have various vlan interfaces configured acting as the gateway for the access networks.

I want both layer 3 switches to form an ospf neighbor relationship and be able to see all networks connected to each other so a host on the Core A side can see a host on the Core B side.

Would I use network statements on each core to advertise the connected vlans, then use passive-interface default to make all interfaces passive, then do a no passive on only the one interface on each core that points to the other core. 

(Question here being if a network or interface is defined in the network statement, and set at passive, does that mean the network in advertised by ospf but just not forming neighbors on that interface)

Heres the sample config im looking to apply

Core A

Router ospf 1

network 172.16.10.0 0.0.0.255 area 0

network 172.16.20.0 0.0.0.255 area 0 (assuming all interfaces are in the 172.16.10 and .20 range)

passive interface default

no passive interface gig  1/0/1 (interface to core B)

Core B

Router ospf 1

network 172.16.30.0 0.0.0.255 area 0

network 172.16.40.0 0.0.0.255 area 0

passive interface default

no passive interface gig  1/0/1 (interface to core A)

Now in addition if have networks not directly connected but currently reachable by a static route. Is it just a matter of redistributing these static routes into ospf as:

ip prefix-list STATIC-REDIS seq 1 permit 192.168.2.0/24

ip prefix-list STATIC-REDIS seq 2 permit 192.168.3.0/24

route-map STATIC-REDIS permit 10

  match ip address prefix-list STATIC-REDIS

router ospf1

  redistribute static <e1/e2> subnets route-map STATIC-REDIS

Thanks

[Jon Marshall · Accepted solution]

Question here being if a network or interface is defined in the network statement, and set at passive, does that mean the network in advertised by ospf but just not forming neighbors on that interface

Yes, exactly right.

And yes to your static question as well.

Just for your information redistributing statics into OSPF will make the L3 device an ASBR in OSPF terms.

Nothing wrong with that, just thought I'd point it out.

Jon

[Mokhalil82]

Thanks a lot Jon, I'm guessing the same concept applies to eigrp as well in terms of advertising and passive interfaces?

[Jon Marshall]

Yes, you would do exactly the same with EIGRP.

Jon