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Within Wireshark, how would one write a display filter for the IP address of the Link State ID within an OSPF Database Description packet? The Link State ID addresses are found within the LSA Header of the DB Description packet.

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capture filter, or display filter? –  Mike Pennington♦ Jul 16 '13 at 18:19
    
Display filter. I modified my question to include that detail. –  THE DOCTOR Jul 16 '13 at 18:49
    
Whoops, sorry I meant to ask for a filter to get the Link State ID. –  THE DOCTOR Jul 16 '13 at 19:35
    
what kind if LSID? Is there a specific LSA type? –  Mike Pennington♦ Jul 16 '13 at 19:47
    
Type 5 (External LSAs) –  THE DOCTOR Jul 16 '13 at 19:58
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1 Answer

up vote 4 down vote accepted

Display Filter by advertising Router-ID:

This display filter will get you close as I can come up with...

ospf.msg.dbdesc == 1 and ospf contains <adv-router-id-as-hex>

For instance, if your advertising router is 1.1.1.1...

ospf.msg.dbdesc == 1 and ospf contains 01.01.01.01

However, the problem is that contains 01.01.01.01 matches any string contents with 01.01.01.01, so both 01.01.01.01 or 01.01.01.01.ff could match... furthermore, it's possible that some other packet in the DBD also contains a reference to that router-id.

Display Filter by advertising Link-State ID:

This is a little easier, because there is a better chance to find a unique string; as long as you know the type of LSA you're looking for. The OSPF RFC requires the packet to get sent with <lsa-type-4bits>.<link-id-4bytes>, so the display filter is:

ospf.msg.dbdesc == 1 and ospf contains <lsa-type>.<link-id>

For example, the display filter to find a Network Summary LSA (LSA Type 3) with the ID of 10.4.27.0 (hex 0a.04.1b.00):

ospf.msg.dbdesc == 1 and ospf contains 03.0a.04.1b.00

Another example, the display filter to find an External LSA (LSA Type 5) with the ID of 10.4.27.0 (hex 0a.04.1b.00):

ospf.msg.dbdesc == 1 and ospf contains 05.0a.04.1b.00

FYI, these are the numbers corresponding to the LSA types

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This was extremely helpful, thank you very much! –  THE DOCTOR Jul 17 '13 at 15:04
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