Comcast Static IP Changed With New Modem?

Has anyone run into the situation where their static IP address from Comcast (on the business class cable modem Internet service) was changed when the modem was replaced?

We have a remote site that uses Comcast as a backup Internet connection and when we went to use it recently our VPN tunnel would not establish. After working with the Comcast support group we discovered Comcast changed our static IP address. I am working through trying to figure out the when and the why with Comcast still and suspect it was changed when the modem was replaced back in December. The modem was replaced by Comcast as our previous modem was apparently EOL'ed.

We're now setting up additional monitoring to verify the accessibility of our remote site via the Comcast connection so we don't have any future uh-ohs when we need to use our backup connection and it too is not fully functional.


Seen this happen quite often with Comcast. They simply didn’t provision the new modem. A simple call to them should correct it. Done it two or 3 times in the past 6 months.


Justin Wilson
Managed Services – xISP Solutions – Data Centers
Podcast about xISP topics
Peering – Transit – Internet Exchange

Yes, this is very common. You are lucky to even get a working static IP
when they replace a modem. A lot of times they forget to assign one or
assigned one that doesn't work. No, most of the time they won't tell you
the IP changed.

Couple time I was told where my IP and default gateway wasn't in the same
subnet. (example, static IP was x.x.x.4/30 and default gateway was
x.x.x.3). Surprisingly, it didn't work. It took me 30 minutes each time
to convince them that won't work.

With Time Warner Cable in my region that is expected 100% of the time.
Every single cable modem replacement requires you to initialize the static
IP configuration. I expect the cable operators to operate similarly.

Josh Luthman
Office: 937-552-2340
Direct: 937-552-2343
1100 Wayne St
Suite 1337
Troy, OH 45373

I've had a similar mistake happen with TWC. It's most likely a glitch in
their config system which should use the gateway's mac address in order to
assign a static IP on the docsis modem. Tech support should figure this out
pretty quick without escalating it much further. I've had an instance where
a second line/modem was added with the same gateway IP, and that brought us
down for over a day until they got around to fixing it.

My suggestions is to always keep your gateways/edges monitored with a
service like Monitis. I use ping monitors every single minute from three
different locations in the US (abroad available too) and get email/SMS/call
whenever something fails once, twice, etc from one, two or more locations.
Really cool monitoring system.

Hope this helps.