Re: [EXIM] Sender verification and DNS lookups

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Szerző: Adrian Bool
Dátum:  
Címzett: hostmaster
CC: exim-users, Tim Cutts
Tárgy: Re: [EXIM] Sender verification and DNS lookups
On Mon 12 Jan, Philip Hazel wrote:
> On Mon, 12 Jan 1998, Tim Cutts wrote:
>
> > 16:43 mole:~> nslookup -querytype=mx mail.zoo.co.uk
> > Server: mole.bio.cam.ac.uk
> > Address: 131.111.36.9
> >
> > *** mole.bio.cam.ac.uk can't find mail.zoo.co.uk: Server failed
> >
> > which took a long time to appear (some sort of time out, I suppose). I'm
> > not much of a DNS expert, so:
> >
> > a) Could this be responsible for the error message that exim is
> > generating and if so,
>
> Yes. It's looking for the MX record and failing in this way.
>
> > b) Whose fault is it likely to be?
>
> The maintainer of the nameservers for zoo.co.uk. They seem to be broken:
>
> ursa$ dig @NS0.ZOO.NET.UK. mail.zoo.co.uk. mx
>
> ; <<>> DiG 2.1 <<>> @NS0.ZOO.NET.UK. mail.zoo.co.uk. mx 
> ; (1 server found)
> ;; res options: init recurs defnam dnsrch
> ;; got answer:
> ;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 10
> ;; flags: qr rd ra; Ques: 1, Ans: 0, Auth: 0, Addit: 0
> ;; QUESTIONS:
> ;;      mail.zoo.co.uk, type = MX, class = IN

>
> ;; Total query time: 5167 msec
> ;; FROM: ursa.cus.cam.ac.uk to SERVER: NS0.ZOO.NET.UK. 194.216.59.2
> ;; WHEN: Mon Jan 12 16:56:35 1998
> ;; MSG SIZE sent: 32 rcvd: 32
>
> Note that "SERVFAIL" status. However, it seems perfectly capable of
> returning A records. I suspect some configuration shambles, or maybe
> bugs in the actual zone file. I have once before seen another DNS server
> in the same state, but never discovered what actually caused it.
>
> The other one seems to be totally dead:
>
> ursa$ dig @NS1.ZOO.NET.UK. mail.zoo.co.uk. mx
>
> ; <<>> DiG 2.1 <<>> @NS1.ZOO.NET.UK. mail.zoo.co.uk. mx
> ; (1 server found)
> ;; res options: init recurs defnam dnsrch
> ;; res_send to server NS1.ZOO.NET.UK. 194.216.59.3: Connection timed out
> ursa$
>
> There is some tie up between zoo.co.uk and zoo.net.uk; something has got
> confused, I suspect. One can do an entire DNS zone
> transfer for the zoo.co.uk zone, and all looks well in there, with no MX
> record but just an A record for mail.zoo.co.uk.
>
> Ha! As I write, it seems to be working again...


Not properly though...

> nslookup

Default Server: localhost
Address: 127.0.0.1

> set q=soa
> zoo.co.uk.

Server: localhost
Address: 127.0.0.1

Non-authoritative answer:
zoo.co.uk
        origin = ns0.zoo.net.uk
        mail addr = hostmaster.zoo.net.uk
        serial = 98010801
        refresh = 10800 (3 hours)
        retry   = 3600 (1 hour)
        expire  = 432000 (5 days)
        minimum ttl = 86400 (1 day)


Authoritative answers can be found from:
zoo.co.uk       nameserver = NS0.ZOO.NET.uk
zoo.co.uk       nameserver = NS1.ZOO.NET.uk
NS0.ZOO.NET.uk  internet address = 194.216.59.2
NS1.ZOO.NET.uk  internet address = 194.216.59.3

>


[ OK - ns0.zoo.net.uk should be teh authorative source for mail.zoo.co.uk
- let's as him... ]

> server ns0.zoo.co.uk.

Default Server: ns0.zoo.co.uk
Address: 194.216.59.2

> set q=a
> mail.zoo.co.uk.

Server: ns0.zoo.co.uk
Address: 194.216.59.2

Non-authoritative answer:
Name:    mail.zoo.co.uk
Address:  194.216.59.4


At this point ns0.zoo.net.uk should be returing an Authorative
answer. The above state tends to screw things. I've seen this
a few times in our own DNS - and is usually caused by a silly
typo in the DNS file, such as a ',' in place of a '.' etc...

> mail.zoo.net.uk.

Server: ns0.zoo.co.uk
Address: 194.216.59.2

Name:    zoo5.zoo.net.uk
Address:  194.216.59.5
Aliases:  mail.zoo.net.uk


mail.zoo.net.uk. does not seem to be suffering - so the problem
really shoul dbe in te zoo.co.uk file somewhere... I could imagine
it is quite big though. To help me find the culprit list time
I used a program called nslint (or dnslint? mmm) which (after cutting
a lot of warnings out) lead me to th problem....

Regards

aid


-- 
Adrian J Bool            | mailto:aid@u-net.net
Network Operations        | http://www.noc.u-net.net/
U-NET Ltd, UK            | tel://44.1925.484461/



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