“Comcast is a tool designed to simulate common network problems like latency, bandwidth restrictions, and dropped/reordered/corrupted packets.”
Accurately named network distortion tool
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Tag Archives: comcast
DIY Ground-based Ion Cannon
Hobbit’s netcat can be used to vomit forth network traffic as fast as your machine can generate it. We don’t need no steenkin’ LOIC!
Anyway, I needed to test a WAN pipe to see if Comcast was delivering the bandwidth we’re paying for – we’re supposed to have a 200 Mbps link to Boston.
[root@monster ~]# yes | nc -4 -u -v -v -n remotehost.boston.com 9
The yes command just screams “yes!” incessantly, like a teenage boy’s dream girlfriend. We pipe the output to netcat, and force it to use UDP and IPv4 to send all the yes traffic to a host in Boston. UDP port 9 is the “discard” service, of course, so the machine at the other end just throws the traffic away. We already constantly monitor all the routing nodes in the path so we can see and graph what happens to the packets in real time.
Turns out the host can generate 80Mbps, sustainable indefinitely. That goes into the 200Mbps Comcast pipe… and only 4Mbps comes out the other end! Thanks, netcat! Time to call Comcast!
Don’t do this if you aren’t ready to deal with the repercussions of completely smashing your network. Saturating interfaces, routers and pipes will severely impact normal business routines, and should be saved as a last resort.
Comcast DNS highly unreliable
Today we finally solved our email mystery. The reason some people could not get their email from their homes was that they were using Comcast as a service provider.
Querying Comcast’s DNS servers at 75.75.75.75 and 75.75.76.76, we discovered that our domain won’t resolve there at all, and even with the domains that do resolve properly there’s between 20% and 50% packet losses. Comcast’s DNS is broken.
A little googling around shows that these problems have been continuously reported by Comcast customers since at least 2006, and Comcast has never fixed it. This has been broken for so long that linux-based home router systems like DD-WRT actually support several workarounds!
We’re a Comcast Business Internet customer, and the people failing to communicate with our site are Comcast Home Internet customers (typically “Triple play” buyers) so this is a case where they are actually failing to provide a critically important customer service to both sides of their business. Our users who have Verizon FIOS are working fine, despite Verizon’s long standing practice of unethical DNS hijacking.