Q:

I'm pinging a server and getting a response, but the server is OFF

I have a server (a simple XP box) on my home network at 192.168.11.2.  I've been having trouble accessing it from my Mac, due to a change in 'location settings'.  So I'm trying to work it out.  I found I could ping the XP server from the Mac, but not connect via samba.  I then discovered I could only get a ping response when the Mac was connected to the internet.  I switched off the server, and the 192.168.11.2 ip address still gave a reply - TTL=60  
This is where my knowledge of ip networking comes unstuck.  Am I in fact pinging an address served by the ISP, and if so, why would it be a 192.168?
Any help, suggestions, most welcome for this ip ignoramus!

A:

When you send out a ping, it routes to a ping server, and the ping server sends back a ping-reply.  If you're able to get a ping-reply from 192.168.11.2 when the XP server is offline, then you're not pinging the XP server.  You're pinging something else.
This could mean that your Mac is on a different subnet where 192.168.11.2 is a different machine.  It could also mean that your XP machine has changed IP addresses (and another device now uses that IP address).
If you're on a home network, make certain that your mac is at an IP address of 192.168.11.X (or something else in the subnet), the server is 192.168.11.2, the default gateway is 192.168.11.1 (or something else in the subnet), and the subnet mask is 255.255.255.0 (or 255.255.X.0 depending on your exact configuration).  Make sure that your default gateway and subnet mask are the same on both the server and the Mac - and are within the subnet (which should be 192.168.11.X if the subnet is 255.255.255.0).
You should also check your router and verify that it has assigned the correct IP addresses to both your XP server and Mac (assuming you're using DHCP instead of static IP addresses).  You should be able to access your router configuration by going to the default gateway (most likely 192.168.11.1).

