DNS order in /etc/resolv.conf . How does that work

[Barry Margolin]

In article <200E2FA22B2AD2119AC000104B6A0A8601E95716 at PSBMAIL1>,
Bhangui_S  <Bhangui_S at bls.gov> wrote:
>General question apologizes if it has been answered before.

I don't think it has been answered here recently, but it's certainly
answered in the DNS & BIND book.  I think you owe Cricket some $$, not just
apologies.

>If the Server  A or the named on Server A dies will the queries be left
>hanging or immediately the Server B should pick up and answer the queries. I
>thought that in the event this happened Server B will pick up
>instantaneously. But apparently that did not happen . Is there a setting
>somewhere which one has to set so that it picks up the second listed server
>immediately if Server A does not respond. Could somebody throw some light on
>this so that I  can understand the proper use of the  DNS order.

The only way that you know that A is down is due to a timeout waiting for a
response.  The resolver will send a query to A, wait a few seconds, and
then query B, wait a few seconds, and then query C.  If this times out it
will repeat the process with a longer timeout for each server.

Also, it doesn't remember from one lookup to the next that A was down, so
there will be a delay before asking B for *every* name you look up.  So
make sure that A is a reliable machine.

The full details are on p.107 of the book.  Note: you can't test this with
nslookup.  It uses a different lookup order; instead of ABCABCABC it uses
AAABBBCCC.

-- 
Barry Margolin, barmar at genuity.net
Genuity, Burlington, MA
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