ospf network statement

[amms68958]

Hi,

Whats the meaning of the staement"network 0.0.0.0 255.255.255.255 area 0 in ospf .I think all my network is under area 0.Am I correct..?

Thanks in advance..

[paddyxdoyle]

I belive this means that OSPF will be running on all interfaces on your router and indeed the area ID will be 0.

HTH

Paddy

[jdilley]

Typically in an OSPF implementation you would have the specific networks or interfaces that you want to participate in OSPF. Example:

router ospf 1

network 10.1.1.0 0.0.0.255 area 0

network 172.16.1.0 0.0.0.255 area 0

The statement you are refering to will activate ospf on any network you have configured on that router and all those networks will be in area 0 which may or may not be what you want

[amms68958]

Hi,

Thanks for your replies....One more silly doubt I got....Whether it is valid if I give network 255.255.255.255 0.0.0.0 area 0.

Thanks..

[Kevin Dorrell]

That would not be valid. It means the single broadcast address, which would not correspond to any interface. I don't know whether the router would reject it, or simply not implement anything.

Kevin Dorrell

Luxembourg

[Harold Ritter]

Bear in mind that the only purpose of the network statement is for the ospf process to determine which interfaces are attached to which area based on the interface primary IP address. This command will not be rejected by IOS but will have no effect whatsoever since no interface has an IP address of all one.

Hope this helps,

[Kevin Dorrell]

Harold, just out of curiosity, if you have a primary address on an interface that falls within OSPF the network list, and a secondary address that does not, will the secondary address be distributed in OSPF or not? I'm away from the lab at the moment, and I don't have the chance to test this out.

Kevin Dorrell

Luxembourg

[Harold Ritter]

You need a network statement that includes the secondary ip address for this one to be advertised as part of the router LSA. Bear in mind that adjacency will be not be established using the secondary IP address.

Hope this helps,

[Kevin Dorrell]

Thanks Harold. So you are saying also that if the secondary address is in the network list, but the primary is not, then it will not form any adjacencies on that interface, even if there are other OSPF routers on the secondary subnet?

But I suppose it will still include the secondary address in the LSA to other interfaces, since it is not necessary for an interface to have an adjacency for it to appear in an LSA. Right?

Kevin Dorrell

Luxembourg

[Harold Ritter]

Correct, the primary IP address needs to be covered by a network statement for the adjacency to be established.

Correct, the secondary IP address subnet would still be included in the LSA type 1 but no LSA type 2 would be generated.

Hope this helps,

[Kevin Dorrell]

Thanks once again Harold for your guidance. If ever I make it to CCIE, it will be in no small measure to your help.

Kevin Dorrell

Luxembourg

[Harold Ritter]

Kevin,

you are very welcome and good luck on your CCIE.