[CentOS] DNS is confusing! (I really need some help understanding!)

Paul Heinlein heinlein at madboa.com
Fri Oct 9 18:38:53 UTC 2009


On Fri, 9 Oct 2009, ML wrote:

> So, Comcast, 13 public IP's bound to my modem.
>
> Each public IP has a DNS name from comcast (they assign it
> automatically) like:
>
> 173.13.167.209 --> 173-13-167-209-sfba.hfc.comcastbusiness.net
>
> I created a DNS entry at GoDaddy for 173.13.167.209 that is
> 'inhouse.theindiecompanyllc.com'
>
> When eth0 is alive, I see that it tells me my name is 
> 173-13-167-209-sfba.hfc.comcastbusiness.net since I am using a 
> comcast DNS Server.
>
> So if I setup my own internal caching name server for 173.13.167.209 
> then I have a third name or can I just use the GoDaddy DNS entry I 
> gave it? Do I then set my systems to use my local name server for 
> their information and not Comcast? How does that effect internet 
> browsing where I dont have entries for google.com, etc in my local 
> name server?

Others have mentioned contacting Comcast to ask for a change in the 
reverse-pointer they publish to the world. That's the best solution, 
albeit one out of your control.

If your concern is mostly internal name resolution, you can tell your 
local DNS server that it's authoritative for 173.13.167.0/24 and set 
up local A and PTR entries. Obviously, you're not really authoritative 
for that subnet (Comcast is), but it allows you to control how your 
network resolves all the addresses you've been assigned, presumably 
173.13.67.208-223. The rest of the world will still see Comcast's 
names, but your network will resolve them as you'd like.

> Lastly, If I have two NICS (one is 173.13.167.209 and second private
> internal IP) For my local name server I would have two entries, one
> for public and one for the private card so I can do something like
> 'inhouse.local' and get intranet or ssh inhouse.local, etc correct?

Just tell your local DNS server that it's authoritative for whatever 
subnet you're using for your private internal IP, set up the zone and 
revp files, and you're in like Flynn.

> I see that Paul Heinlin put out a DNS tutorial here: 
> http://www.madboa.com/geek/soho-bind/ Paul, I appreciate this!

Thank Carla Schroder. She asked me to write that bit for her 
(excellent) Linux Cookbook and encouraged me to publish my original 
version of it...

-- 
Paul Heinlein <> heinlein at madboa.com <> http://www.madboa.com/


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