"/etc/resolv.conf" revisited

[Barry Margolin]

In article <200E2FA22B2AD2119AC000104B6A0A8601FEDE52 at PSBMAIL1>,
Bhangui_S  <Bhangui_S at bls.gov> wrote:
>Hello
>	Many including Barry had answered some of my queries about the
>functioning of the order of the name server in "/etc/resolv.conf" but it
>looks like I still have some confusion.
>
>I am on Solaris Box whose e"/etc/resolv.conf" looks like
>
>
>domain 		xyz.com
>
>nameserver	IP address of M/C A (Primary Internal DNS server, A solaris
>Box, Bind 4.9.4)
>
>nameserver	IP address of M/C B (Secondary Internal DNS Server, NT box)
>
>nameserver       IP address of M/C C  (Our DNS outiside the firewall with
>very few internal entries, Bind 8.2.2P5)
>
>With the above configuration I am able to resolve all the internal names to
>an IP addr as defined in the Internal DNS.
>
>Now the questions I have are.
>
>1. With the above configuration if something happens to bind on M/C A . M/C
>B should pick up and should answer to the queries with a lag of whatever
>time bind will spend querying the m/c A and I think that is 5 seconds. Is
>that correct? 

Correct.  This is as described on p.107 of the DNS & BIND book.


>Now if the order in "/etc/resolv.conf is changed to the following
>
>domain 		xyz.com
>
>nameserver 	M/C C	(External DNS outside the firewall)
>
>nameserver	M/C  B   (Secondary Internal DNS Server)
>
>Following discussions pertaining to the configuration above.
>
>Now if I try to resolve a Internal name (the name is not defined on M/C C) I
>believe as long as the named is alive on M/C C I should get a response as
>unknown host. Now if the named for some reason is not up and running or is
>dead on M/C C than it will wait for a response from M/C C and after that 5
>seconds interval query M/C B and I should be able to resolve that name as
>the M/C B knows about the internal name" Is this correct 

Correct.

>So can I state this that as long as BIND is running on M/C C and it responds
>to a query it will never roll over to M/C B even though it cannot resolve a
>Internal name. It will go and query M/C B only if M/C C is down or BIND on
>M/C C does not respond to the DNS queries.

Correct.

Failover to backup nameservers only occurs when a query times out, not when
a response with an error comes back.  The purpose of multiple nameservers
is to provide fault-tolerance when nameservers crash.

-- 
Barry Margolin, barmar at genuity.net
Genuity, Burlington, MA
*** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.