Question : Find 2 devices with same IP accross WAN

I've had situations where 2 network devices have the same IP address, but they are distributed across WAN:

e.g.
The device reporting a duplicate IP issue is in Seattle, I - the admin am in San Francisco, but the OTHER device could be anywhere from New York to Nashville.

What technique have you used to track stuff like this down?

Answer : Find 2 devices with same IP accross WAN

O.K., you can't pick up a device and move it and have it still responed, unless you have the same IP subnets at two different locations.

The 1st step is to find out what all the IP subnets are at all of the locations and then figure out what sites have duplication or over lapping IP subnets.  Clean that up and your problem will go away.

You should be able to figure this out by looking at the routing table on the router at your site, or in this case what ever is the VPN device at your site.