Pinging domain names resolves but times out

First, few assumptions:

• you want to do that programatically, and not looking at the leds
• you don't know the current IP of xbox
• you know the subnet that dhcp gives IPs from

To list IP/MACs currently known to system: cat /proc/net/arp

So you would have to ping every IP from the subnet, then check the arp table, and to be sure ping the IP.

Something like:

ping -c 1 `cat arp | grep "00:12:34:45:78:AB" | cut -d" " -f 1` >/dev/null; echo $?

Will output 0 if Xbox is answering to pings, and 1 otherwise. Depending on what you want to do, you can do some if on $? or something.

Did you set the gateway on the D-link when you set it as an AP?

Since pings work from local network, but not from other networks, this could be the most obvious problem, and easiest to verify.

After edit:

Did you check the firewall rules on the AP? Some allow pings only from "LAN" networks (not from WAN), or directly attached networks.

With default firmware, it's hard to debug, but if there's *wrt on it, you can try testing with tcpdump if packets come to the AP (they should), and check the firewall rules.