I've got a stupid tcpdump question, and I'm not sure what I'm missing
here. (tcpdump is what I'm using, but I'm thinking I need a different
tool or just learn how to use tcpdump correctly)
My "requirement" is that I be able to plug in my laptop (Linux for this
example) and be able to instantly see what the IP address of a network
device (AP, switch, hub, router, etc) using just a cross over cable.
Up to this point, I've been using tcpdump (e.g. with the flags -i arp)
and it's worked, but it's not working lately, and I suspect that it's
because some of the devices are on a different subnet entirely.
e.g.
tcpdump -i eth0 arp
If I'm on the same subnet as the device, I'll get back tons of info,
including the right IP and MAC address.
If, however, it's a weird different IP, I don't see that same info.
In the field, I sometimes know the password of the wireless unit, but
the IP address is whacked (sometimes it's something stupid, like
1.2.3.4). To make matters worse, the wireless units are meshed to other
units, so there are dependencies on this "working" system, and I can't
just reset them like I could if it was all from scratch. I have to
change the IP address of this unit eventually, as remotely managing a
bogus IP like 1.2.3.4 is a pain in the butt.
So, here's my scenario: in the end of the day, I want to be able to get
in a cherry picker, plug in the bottom of a unit, and slam out one
command (or a set of commands) and instantly "see" the IP address of the
unit so that I can remote in locally and change it's IP. (No, there's
no console connection on this box, which is half my problem).
(A little back history: these units come defaulted on a 10net network,
but then they, and then they're updated to the right 192 or 172 network
or whatever. However, admins often forget to write to memory after that
config change, and if I have to get in it afterwards, it's very
difficult without resetting the unit, as these units don't have console
ports and the only way to get the password back is to reinitialize the
unit with a dongle in the battery, thus nuking the whole config and
starting from scratch. Having this quick fix would be a godsend.)
Thanks, guys. I'm all ears if you have a better way of possibly doing this.
