ospf data length

[joeblough]

Pardon this post if it is strictly a Windows issue.

I have a 2514 router connected to a pc running w2k server with routing enabled. Both are running ospf. Both generate error messages when attempting to update.

The error log in windows says "rejected ospf packet because data length was 48 but length calculated for the IP header field was 60".

The error message on the router was somewhat obtuse for me (new to routing), but made reference to packets being rejected due to some violation.

I'm just toying around in a lab setup, so it's nothing critical.

If anyone can point me toward some info on this situation I would appreciate it.

Thanks

[ruwhite]

Interesting. :-) So, I've never tried hooking up a cisco to a windows machine, but wouldn't have expected this, exactly. There are two lengths in an OSPF packet (just like in TCP), one of which describes the length of the OSPF data, and the other of which describes the length of the entire IP packet. Thus, it's something like this:

IP(length of IP)(OSPF(length of OSPF)..)

If you add the length of the OSPF information to the length of the IP header, you should come up with the length of the IP packet, in theory. Well, the two implementations are computing their lengths differently, or something, because they are both complaining about the two lengths not matching. I could kindof understand it on the windows side. OSPF does use a set of extensions to the OSPF hellos called link local signalling that would make these two not match (intentionally). I don't know about the cisco giving those error messages for the windows router, though....

You might try turning LLS off, depending on the version of code you're on:

http://www.cisco.com/en/US/products/sw/iosswrel/ps5207/products_command_reference_chapter09186a00801a807f.html#wp1036468

is how you can turn it off, to see if that's the issue.

:-)

Russ.W