Difference between A= and NS= fields in 'learnt' part of Lame Server message?

[Barry Margolin]

In article <386FCB1E.46EBA66A at aset.com>,
Jon R. Kibler <Jon.Kibler at aset.com> wrote:
>Consider the following lame server message:
>
>	Dec  7 17:50:58 asethost named[136]: Lame server on '1.2.151.128.IN-ADDR.ARPA' 
>	     (in '151.128.in-addr.arpa'?): [128.151.128.52].53 'NS.UTD.ROCHESTER.EDU': 
>	     learnt (A=128.105.2.10,NS=128.8.10.90)
>
>It is clear what is lame, but what isn't clear is how to interpret the
>learnt part of the message when A= and NS= are different. What is the
>difference between A and NS? 

That section of the message tells you from whom you learned the information
used to make the query that turned out to be lame.  It says that you
learned the record:

151.128.in-addr.arpa. NS  ns.utd.rochester.edu.

from 128.8.10.90 (d.root-servers.net)

and the record:

ns.utd.rochester.edu.  A  128.151.128.52

from 128.105.2.10 (dns.cs.wisc.edu).

This is useful to know because there can be several possible reasons for a
lame server:

1) The delegation NS record is wrong;

2) The server that the domain is delegated to is misconfigured;

3) The delegation records and server are both correct, but there's an
incorrect glue A record that's causing you to query a different server than
you should be.

The two fields in the learnt section of the error can help you distinguish
cases 1 and 3.

-- 
Barry Margolin, barmar at bbnplanet.com
GTE Internetworking, Powered by BBN, Burlington, MA
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