OSPF wildcard

Jun 09, 2005 11 Replies

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Tim Pope 21 years ago

For OSPF network commands there are plenty of examples in the Lammle book and Cisco book for nice, neat subnet masks with all 1's in an octet.

255.255.255.0 for example would yield a wildcard of 0.0.0.255.

But what about the network config for a mask like 255.255.255.240 ? If my IP address is ..say...170.50.10.17.

Would it be ...network 170.50.10.0 0.0.0.15 area 1

Or... network 170.50.10.17 0.0.0.15 area 1

Or something else?

Also it seems that you could just use wildcard 0.0.0.0 for all you network commands and only the wildcard notation for summarization right? Would that work on the exam?

Tim

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Bill 21 years ago

Hi Tim,

If your ip address is 170.50.10.17 and snm is 255.255.255.240, your network range is

170.50.10.16 through 170.50.10.31 so you would use

network 170.50.10.16 0.0.0.15 area 1

170.50.10.17 is wrong because it is a host address.

170.50.10.0 is wrong because it is a different subnet

The network part of the statement should contain the subnetwork address, not a host address.

The exam will not allow you to do it any other way.

Bill

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Make 21 years ago

This works also: network 170.50.10.17 0.0.0.0 area 1

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Tayfun Tuna 21 years ago

I would say

network 170.50.10.16 0.0.0.15 area 1

because, as the sunben mask is 255.255.255.240, this IP .17 belongs to

10.50.10.16 network *first usable IP is 17)

if the ip was 10.50.10.82 255.255.255.240

network 170.50.10.80 0.0.0.15 area 1

Tayfun

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Cas 21 years ago

Yep if you want to only match host 170.50.10.17. If you need to match

170.50.10.17's subnet, it will not work.

Cas..

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Make 21 years ago

Actually it works. It adds the network to ospf, not the host. It looks the right mask from the interface.

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Doan 21 years ago

It's by design. The network statement indicates which interfaces will participate in the OSPF processs. Since you can have only one interface in a particular subnet on a router, you can specify either the interface or the subnet.

Doan

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Cas 21 years ago

Strange... Is that by design, or a coincidental side effect ?

Just curious...

Cas...

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Jonathan 21 years ago

Yeah, it will.

The router will change it to the correct subnet.

Jonathan

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Jonathan 21 years ago

By design.

The router realizes what you are trying to do and does it.

Jonathan

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Cas 21 years ago

Clear ! Thanks...

Cas.

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Ivan Ostres 21 years ago

Router will not change the configuration in this example. The only thing you're matching here is the interface (which is always /32) and router will pick up the subnet which is defined on matched interface (in ospf database), except if that interface is loopback. Then it will pick it as /32 by default.

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