changed ISP and router, problems with XEP setup

[wuench]

My point was that you don't have to be on the same network address space (PC and XEP) to configure the XEP via ElkRP. To show this, I just changed the IP address on my PC to a completely different network (172.20.1.x) while I left my XEP settings alone. I could still connect via ElkRP and get to the settings page to change the IP address (see attachment).
 
However, with this configuration, I would not be able to ping the XEP from my PC because of the network differences.

 
You are absolutely correct, but there is some luck involved in that working.  If a device tries to talk to another that is not on it's network, it will send it to the gateway (router) address.  It works if the router broadcasts the ARP for the PC to the Elk (ProxyARP).  Most, but not all routers will do this by default and it can be disabled.   Also the Elk does not have a correct gateway address so initiation from that side would fail.  It would also work, if the devices are doing inverse arps the tables will get populated, but not all devices do that either.  
 
It is safest to put both devices on the same network (subnet and mask matching), then you are assured it will work for all protocols in all directions without worrying about the router configuration.

 

[tmbrown97]

Yes - not to nitpick but for the sake of accuracy for those not familiar with networking that follow this thread:
 
The serial connection is between the XEP and the M1; it has very little to do with how your computer talks to the M1 (the serial connection at least) - your computer is using the TCP/IP network to talk to the XEP which has a direct connection to the M1; therefore you must have working connectivity between your PC and the XEP.
 
I haven't used Ethereal to trace how the M1's lookup goes - I've found it to be pretty unreliable (The XEP that is)... but it could be one of the methods wuench states above; TCP/IP is just one method for two devices on the same physical network to communicate - there are others that require no "IP Address" at all - and work via the devices' MAC Addresses directly.  With that, there are a lot of devices that you can connect to on a network and they have utilities such as the Find XEP that let you find a device by scanning MAC addresses and issuing some set of ARP or other commands to get info about them from the networking environment - but can also communicate outside of TCP/IP enough to at least send a command to it saying "Set your IP to this".  Essentially meaning IF the manufacturer builds this in AND provides the tools to do it, you can get two devices to talk even if they're not on the same TCP/IP subnet.