Technical: Networking – Comcast – What is your FQDN

Technical: Networking – Comcast – What is your FQDN

As previously mentioned, I have a Comcast Account. And, I get 5 IP Addresses.

It is relatively easy to get an IP Address for a new device; this time a linux test box.

So I have an IP Address. Confirmed it using ifconfig.

But, what is my Fully Qualified Domain Name?

Yes, from the outside world, I can connect using IP Address, but I am not down with remembering numbers.

So I looked on the Net and confirmed comcast’s publicly accesible DNS Servers:

  • 75.75.75.75
  • 75.75.76.76

BTW, the web page (http://forums.comcast.com/t5/Home-Networking-Router-WiFi/Change-In-DNS-Servers/td-p/1375137) is quite useful, as it brings other information and tools, as well.

Anyways back to our original need, what name do people target?

Well just issue host and pass in the IP Address:


Syntax:
   host <ip-address>

Sample:
   host 24.6.1.16

Output:

host against comcast

So that is our FQDN:

c-4thoctet-3rdoctet-2ndoctet-1stoctet.hsd1.ca.comcast.net.

There are a couple of things that makes this work.  It appears that Comcast DNS Servers are configured:

  • with Reverse DNSes for the IP Address Pool that they own
  • The DNSes are updatable — That is each time their DHCP leases a new IP Address, the DHCP Server updates their DNS Server

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