[bdNOG] Yahoo Mail can't communicate with my domain servers
Brian Candler
brian at nsrc.org
Thu Dec 24 02:57:53 BDT 2015
On 23/12/2015 20:27, Anurag Bhatia wrote:
> Your reply is bit confusing from part below since I own and manage the
> test server (server7) not Jasim's server. :)
>
> Keep in mind I am not running btraccl.net <http://btraccl.net> DNS
> servers. It's Jasim who is having trouble. But yes I get hints you are
> sharing for troubleshooting. :)
>
The confusion is entirely mine; I apologise for spreading it :-)
So, what you can do on your side is:
# in one window
sudo tcpdump -i eth0 -nn -s0 -v host 103.9.185.229 or icmp
# in another window
dig @103.9.185.229 <http://103.9.185.229> btraccl.net
<http://btraccl.net> mx
Probably you will just see your outbound packets, but you *might* see
ICMP "Admin Prohibited" coming back. If so, that's hard evidence of
filtering, and will show exactly where the filtering is taking place,
which is extremely useful.
If you don't mind sharing your IP address (privately with Jasim if you
prefer), then:
1. Jasim can try a traceroute to that address and see if it works.
(Presumably it does, because of the end-to-end ping and traceroute you see)
2. Jasim can run tcpdump on the DNS server and look for traffic from
your IP while you send a query, and see if the query arrives or not. It
might be that the inbound packets are arriving, but the responses are
being filtered.
I think you're right it's most likely a broken firewall somewhere, but I
*have* seen ISPs intentionally block UDP 53/123 in a misguided attempt
to "protect" their customers, and/or to force them to use the ISP's own
caching resolver (for example because they are doing anti-porn or
anti-warez filtering in DNS)
Another outside possibility is that there is a layer2 bonded pair of
links in the path, and one of the links is faulty. These typically use a
hash of source/destination IP and port to decide which link to send the
packet over. This could mean that ICMP is taking one path but UDP port
53 taking a different one.
Out of interest: if you do "telnet 103.9.185.227 25" from server7, does
it connect successfully? This would imply that if Jasim gets a proper
secondary DNS, the mail would flow happily (and also more strongly
points the finger at UDP port 53 filtering)
I see:
$ telnet 103.9.185.227 25
Trying 103.9.185.227...
Connected to 103.9.185.227.
Escape character is '^]'.
<< long delay here; implies reverse DNS lookup problems at the server
side >>
220-cp1.btraccl.net ESMTP Exim 4.86 #2 Thu, 24 Dec 2015 02:55:58 +0600
220-We do not authorize the use of this system to transport unsolicited,
220 and/or bulk e-mail.
Regards,
Brian.
P.S. For comparison, here's traceroute from a VM in the UK. The last few
hops are the same as you see, but in this case it's not going via
airtel.in. That *might* be where the problem is occuring.
$ traceroute -w1 103.9.185.229
traceroute to 103.9.185.229 (103.9.185.229), 30 hops max, 60 byte packets
1 213-138-103-3.no-reverse-dns-set.uk0.bigv.io (213.138.103.3) 0.578
ms 0.575 ms 0.612 ms
2 te3-4.cr2.man.bytemark.co.uk (91.223.58.64) 0.811 ms 0.952 ms
1.073 ms
3 te0-0-1-0.cr4.man.bytemark.co.uk (91.223.58.132) 6.914 ms 7.160
ms 7.248 ms
4 te0-0-1-2.cr1.lon.bytemark.co.uk (91.223.58.27) 7.090 ms
te0-0-2-2.cr1.lon.bytemark.co.uk (91.223.58.25) 7.129 ms
te0-0-1-2.cr1.lon.bytemark.co.uk (91.223.58.27) 7.215 ms
5 81.25.207.213 (81.25.207.213) 7.186 ms 7.194 ms 7.198 ms
6 ae-7.r23.londen03.uk.bb.gin.ntt.net (129.250.6.54) 28.439 ms
12.812 ms 41.834 ms
7 ae-0.r22.londen03.uk.bb.gin.ntt.net (129.250.4.85) 8.765 ms 8.743
ms 8.735 ms
8 ae-3.r00.sngpsi05.sg.bb.gin.ntt.net (129.250.7.21) 194.383 ms
190.415 ms 190.434 ms
9 ae-3.r00.sngpsi05.sg.bb.gin.ntt.net (129.250.7.21) 191.934 ms
194.400 ms 192.356 ms
10 116.51.28.130 (116.51.28.130) 243.758 ms
103-16-152-25-noc.bsccl.com (103.16.152.25) 241.136 ms 239.398 ms
11 103-16-152-25-noc.bsccl.com (103.16.152.25) 241.584 ms
103-16-152-33-noc.bsccl.com (103.16.152.33) 241.600 ms
103-16-152-25-noc.bsccl.com (103.16.152.25) 239.196 ms
12 103-16-155-26-noc.bsccl.com (103.16.155.26) 255.071 ms
103-16-152-33-noc.bsccl.com (103.16.152.33) 243.217 ms 241.485 ms
13 103-16-155-26-noc.bsccl.com (103.16.155.26) 256.580 ms 256.585 ms
po1-ar1-bn1-dh.equitel.com.bd (103.9.186.66) 259.161 ms
14 po1-ar1-bn1-dh.equitel.com.bd (103.9.186.66) 257.245 ms
103.9.186.130 (103.9.186.130) 246.590 ms 248.499 ms
15 103.9.186.130 (103.9.186.130) 248.612 ms 249.879 ms 103.9.185.229
(103.9.185.229) 246.982 ms
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