Comcast SMC Router Issues - Smart Packet Detection

Symptoms:

Intermittent success reaching a website, or high numbers of TCP retransmits when looking at a packet dump. Possible problems with IPSEC client vpns running over UDP or even TCP.

This does not seem to be as much of an issue with site to site IPSEC vpns behind Cisco ASAs and OpenBSD firewalls (as of yet) but we are still tracking this issue.

Goto the SMC router web admin tool:
http://10.1.10.1
login with the username cusadmin passwd highspeed

Disable Gateway Smart Packet Detection

More info:

http://ckdake.com/content/2008/disable-gateway-smart-packet-detection.html
http://www.default-password.info/smc/

One reported case from a net admin via NANOG:
The symptoms are basically complete
loss of connectivity (lasting minutes to sometimes hours), or sometimes
flapping for a period of time. More often than not, a reboot of the
cable modem is required. The most interesting ones involve the
following: a PIX or ASA configured as an EZvpn client, connecting to a
3000 concentrator, authentication over RADIUS. When I go to look at the
RADIUS logs, I see connections from the same box with small intervals.
Timeout is 8 hours, so theoretically I should see 3 connections in a
24-hr period. In some cases, I see dozens, in the most egregious cases,
thousands over a 24-hour period. I am taking that as an indicator of a
really unstable Comcast circuit. We have not had this problem with any
other ISP, anywhere in the country.