[Nmh-workers] [OT] Strange DNS for cyrus.andrew.cmu.edu was: IMAP/nmh, again

[Andy Bradford]

Thus said Ken Hornstein on Thu, 26 Oct 2017 14:22:37 -0400:

> There  is  some  variance  here.  It   seems  that  the  DNS  TTL  for
> 'cyrus.andrew.cmu.edu' is set  to 1 (!) second,  so if it has  to do a
> DNS query it takes noticably longer:

That's  a bit  extreme... I  see that  they have  an MX  record that  is
considerably longer:

$ dnsqr mx cyrus.andrew.cmu.edu        
15 cyrus.andrew.cmu.edu:
212 bytes, 1+6+0+0 records, response, noerror
query: 15 cyrus.andrew.cmu.edu
answer: cyrus.andrew.cmu.edu 21519 MX 10 andrew-mx-06.andrew.cmu.edu
answer: cyrus.andrew.cmu.edu 21519 MX 10 andrew-mx-02.andrew.cmu.edu
answer: cyrus.andrew.cmu.edu 21519 MX 10 andrew-mx-03.andrew.cmu.edu
answer: cyrus.andrew.cmu.edu 21519 MX 10 andrew-mx-01.andrew.cmu.edu
answer: cyrus.andrew.cmu.edu 21519 MX 10 andrew-mx-04.andrew.cmu.edu
answer: cyrus.andrew.cmu.edu 21519 MX 10 andrew-mx-05.andrew.cmu.edu

And the  A record  for at  least one  of those  hosts is  similarly much
longer:

$ dnsqr a andrew-mx-06.andrew.cmu.edu
1 andrew-mx-06.andrew.cmu.edu:
61 bytes, 1+1+0+0 records, response, noerror
query: 1 andrew-mx-06.andrew.cmu.edu
answer: andrew-mx-06.andrew.cmu.edu 21455 A 128.2.157.74

But the A record for that name is only 1 second... strange:

$ dnsqr a cyrus.andrew.cmu.edu 
1 cyrus.andrew.cmu.edu:
86 bytes, 1+3+0+0 records, response, noerror
query: 1 cyrus.andrew.cmu.edu
answer: cyrus.andrew.cmu.edu 1 A 128.2.158.26
answer: cyrus.andrew.cmu.edu 1 A 128.2.105.45
answer: cyrus.andrew.cmu.edu 1 A 128.2.158.29

I wonder  what the  purpose of  such a  configuration might  be. Clearly
there's a difference between  their MX for the domain and  the A for the
domain itself so  one wonders what is on  cyrus.andrew.cmu.edu that they
don't want DNS clients to cache those  records, but don't care if the MX
records are cached much longer.

Andy
-- 
TAI64 timestamp: 4000000059f235a2