How to Go Insane Using Comcast

It's simple to go insane when using Comcast as your cable modem provider.

1. Watch as Comcast-provided cable modem goes dead. (Not insane yet).


2. Swap out cable modem at store. (Not insane yet).


3. Plug in cable modem and watch router receive IP address. (Not insane yet. Happy, actually.)


4. Notice machines begin trying to reach 1.1.1.1 when using TCP. (Slight insanity.)


5. Observe that UDP traffic like NTP updates work properly. (Higher insanity level.)


6. Notice that your cannot ping your default gateway. (Insane. Period.)

Apparently when my new cable modem is put on the network, it was given 68.87.96.204 (CPSDNS.selfprov.pa.comcast.net) as its DNS server. This is a really amazing system. Check it out.

orr:/home/richard$ nslookup www.google.com 68.87.96.204
Server:         68.87.96.204
Address:        68.87.96.204#53

Name:   www.google.com
Address: 1.1.1.1

orr:/home/richard$ nslookup www.taosecurity.com 68.87.96.204
Server:         68.87.96.204
Address:        68.87.96.204#53

Name:   www.taosecurity.com
Address: 68.87.96.200

The first 1.1.1.1 IP address is reserved. The second 68.87.96.200 belongs to act02.selfprov.pa.comcast.net, which goes to a www.comcast.net Web server. Apparently I was supposed to not use a site like Google as my home page, but something else that would bring me to the Comcast site so I could "self-provision" my new cable modem.

So why could I update time with NTP? Check out the wonders of 68.87.96.204:

orr:/home/richard$ nslookup clock.isc.org 68.87.96.204
Server:         68.87.96.204
Address:        68.87.96.204#53

Name:   clock.isc.org
Address: 68.87.96.200

That's not correct.

orr:/home/richard$ nslookup clock.isc.org 209.98.98.98
Server:         209.98.98.98
Address:        209.98.98.98#53

Non-authoritative answer:
Name:   clock.isc.org
Address: 204.152.184.72

But guess what -- 68.87.96.200 is running a time server.

orr:/home/richard$ sudo ntpdate 68.87.96.200
Looking for host 68.87.96.200 and service ntp
host found : act02.selfprov.pa.comcast.net
 5 May 20:56:17 ntpdate[874]: adjust time server 68.87.96.200 offset 0.016223 sec

Hence, my insanity. Some applications worked (NTP), others (TCP to certain Web sites) did not. Good grief. By the way, my equipment came with zero setup instructions. I should have just called tech support earlier and said "the Internet is broken," rather than network troubleshoot!