CentOS - Oct 2009 - DNS is confusing! (I really need some help understanding!)

OK, I am confused and DNS is the reason.

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?

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?

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

-ML

ML wrote:
> OK, I am confused and DNS is the reason.
>
> So, Comcast, 13 public IP's bound to my modem.
>   
13 IPs for your modem?  Is this a business account or something?
> 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'
>   
You can use Godaddy to set DNS for 'inhouse.theindiecompanyllc.com' to
173.13.167.209, but to do the reverse, you will need Comcast to delegate
DNS authority to you for the reverse domains.  (For just a few of them,
you would be better off asking Comcast to set the reverse names for you
... don't know if they will do that or not).
> 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.
>   
Doesn't matter what server you use, they should all return this since
Comcast is in control here.
> 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?
>   
I think you are confusing forward and reverse DNS lookups.

A forward DNS lookup is this:

$ host buc.com
buc.com has address 205.245.136.11

A reverse lookup is this:

$ host 205.245.136.11 localhost
11.136.245.205.in-addr.arpa domain name pointer menu.buc.com.

The forward lookup is handled by your Godaddy DNS.  This is all that is
needed for letting someone get to your server by name.  The reverse
lookup must be handled by whoever controls the IP addresses.  This is
usually your ISP (Comcast).  Changing the reverse lookup may not be
necessary depending on what you are trying to do.

If you tell us what you are trying to accomplish we may be able to offer
further suggestions.
> 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?
>   
I'm not sure what you are trying to say here.  The two NICs should not
matter as long as you have them configured correctly.  The system will
use whichever NIC it requires to get to the IP address given to it by
the DNS (or host file, or whatever).

-- 
Bowie

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/