Got a good one here...
I have a home based client on an Embarq DSL line. They have a ZyXel EQ-660R DSL modem connected to a Linksys WRT54GX2 router. THe dsl modem is acting as a router as well. It has a public IP on the WAN side, and uses 192.168.2.1 as its LAN IP.
The Linksys WRT54GX2 gets it's WAN ip from the ZyXel via dhcp. Currently 192.168.2.2. I know, not really a wan ip, it's private, but as far as the linksys is concerned, it's the route to the rest of the world.
WiFi is enabled, with WPA2 encryption.
All has been fine for a while.
Today, I got a call from them that they couldn't check their email. They had internet access. I remoted in, and found that they were unable to ping any IP on the subnet that their email servers were on (which we host). Our network was fine, not an issue there.
A traceroute from the laptop in question showed successful pings to:
192.168.55.1 (the linksys ip)
192.168.2.1 (the zyxel ip)
76.2.x.x (the embarq network)
138.210.x.x (another embarq ip)
then timetimouts for a bit
sometimes it would continue to an alter.net ip, then a level3 ip, but ultimately timeout before our public IP subnet.
I was able to ping my client's public embarq address from one of our servers on that unreachable subnet.
I was able to ping 1 hop away from our subnet from the client's machine, and the traceroute there was fine all the way including right after that 4th hop, where the first timeout was consistently happening when pinging the router for our subnet.
To eliminate this being some crazy problem with the laptop being used, I had them try a second laptop over wifi. Same results.
The linksys has a diagnostic option in the admin interface. It's able to ping and do a traceroute to the subnet in question without issue.
Grasping at straws, I tried having the client connect one of the laptops to the linksys router using an ethernet cable and turn off wifi. POOF! It started working. Full access to that subnet.
I've been doing this a long time, but have never seen anything like this.
If it's a problem with WiFi, how in the world would it get out to the embarq network, but stop after the 4th hop (same spot every time), but not get stuck using a wired connection via the same box? It just doesn't make any sense to me.