[NTLUG:Discuss] Mail server not propagating?

[Greg Edwards]

Nice example.

As someone mentioned where your physical files exist really indicate 
where your master is located.  The terms master, secondary, tertiary, 
etc. are really meaningless.  You have a primary server and everybody 
else is a secondary (or slave but that just muddies the water here) server.

What determines if a DNS server is primary or secondary is whether or 
not it can answer as Authoritary and this is a function of the server 
software.  If the server reads the source files and finds a master type 
it'll answer as Authoritary.  The resolvers don't give a hoot if the 
answer comes from a primary, secondary, or master server unless an 
Authoritative answer is required, which is a small percentage of the 
requests.

One big problem on the net is that you can have as many master servers 
as you can find places to provide the hosting.  This SHOULD NOT be done 
but it is done allot.  What SHOULD be done is to have only 1 master and 
everyone else provides secondary servers.  This practice can work but 
the problem is keeping the master (source) files in sync.

I think the best way to resolve the original problem (updated DHCP 
assigned IP) is to run a local primary server and ask others to run 
secondary servers.  Use long TTL values so that updates are not needed 
on a regular basis.  When a changed IP is realized or say 75% of the TTL 
period has passed automate the updating of the host files and force BIND 
to send the updates to all of the secondary servers (IIRC HUP, but check 
the book or man page).

Now having said that I'll also say that I would not recommend doing this 
either.  Your going to find that you WILL NOT be able to update reverse 
addr records cause you don't own the IP block that your Dynamic IP was 
in.  Trying to host from a dynamic IP just causes more problems than 
it's worth.  Using non static IPs on the net creates traffic that can 
never be resolved due to the reverse addr lookup problem as well as the 
incorrect delivery of traffic while a new address is being propagated to 
countless servers.  Just my $.02.


Bug Hunter wrote:

>   In the dns database, you can have as many name servers listed as you
> wish.
>   
>   Essentially, here is what happens on a DNS query.
> 
>   machine A asks DNS server B what www.ntlug.org is.  B asks root server C
> who handles ntlug.org.  C says use machine D.  Machine D runs the DNS
> server for ntlug.org.  It is queried and is asked, "what are your dns
> servers? (the SOA)",  then the first server in the  list is asked "what is
> www.ntlug.org?"
> 


-- 
Greg Edwards
New Age Software, Inc.
http://www.nas-inet.com