Charter: ICMP being blocked?

[Bob George]

I moved to the area back in July, and have been very happy with
Charter's high-speed Internet offering. The speed's lower for the cost
than what I've used previously (Cox in Phoenix), but there were no nasty
surprises -- until this week.

We had a brief power outage while I was at work. I tried doing a
traceroute and ping to my system from the office, and noted that there
were no responses from within Charter's network (specifically, nothing
after att.net).

On returning home, I verified I had a solid cable light on the modem,
and powered on my system (Debian 3.0) . On boot, I was assigned a DHCP
address, but I could not ping my default gateway, nor any known host
either by name or IP address. I spent some time on the phone with
Charter support, but other than confirming that they too couldn't ping
my gateway address, the tech only suggested that I wait a while.

Curious as to why I would get a dhcp lease but not be able to get out, I
fired up tcpdump and was puzzled to see my system happily making DNS
queries and resolving addresses. I then tried a browser, and was able to
access the 'net normally otherwise.

Everything is working, including games played via NAT'ed internal
systems. I can establish connections from outside to my system on known
ports that aren't normally blocked. But I can not ping or traceroute out
or in.

I'm wondering if Charter has begun filtering ICMP traffic to/from
subscriber addresses as some sort of DoS countermeasure? Or is this
simply a "feature" that I'm experiencing? It's an interesting security
enhancement, but it does deprive me of some useful troubleshooting tools
(as well as their tech support).

Is anybody else experiencing similar problems?

Thanks all,

- Bob