detecting subnet mismatches

[Jeffrey Birtcher]

I have a 3745 in a remote office.  i have a known-good device attached to f0/0, but i cannot reach it...so a known-good device with a suspected bad network config.

i believe that if i could configure my f0/0 to match the 'bad config' i could access the device and reconfigure it, and then reconfigure the f0/0 back to the original config.

i can only do this if i can detect the remote subnet.

-now-

i can dispatch a tech to the site to do some basic config work on the device, try to rebuild it, or figure out what's in there now, but i'd like to know if there's a way to remotely detect what's physically connected to my f0/0 port without visiting the remote site.

i've tried a variety of debug settings, and can't seem to get any response.  broadcast ping?  nope.

any ideas?

thanks!

[Maarten Vervoorn]

I think Trial and error is the best way to go. There are not may options to try a mask. I don't think it would be larger than a /22 so 9 option to try

255.255.255.252 (/30)

255.255.255.248 (/29)

255.255.255.240 (/28)

255.255.255.224 (/27)

255.255.255.192 (/26)

255.255.255.128 (/25)

255.255.255.0 (/24)

255.255.254.0 (/23)

255.255.252.0 (/22)

Be carefull if you device is routing anything. Exclude the network from your routing updates. It could mess up other parts of you network when trying large subnetmasks.

Kind regards,

Maarten Vervoorn

[lgijssel]

When it is a cisco device, you can use "sh cdp nei det" to find out the ip settings.

This works also when the ip settings don't match.

regards,

Leo