Technicolor TG582n FTTC DNS resolution issues?
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- Re: Technicolor TG582n FTTC DNS resolution issues?
Technicolor TG582n FTTC DNS resolution issues?
24-10-2015 2:12 PM
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I appear to be having some name resolution issues which I spotted with my own mail server I run on a Synology NAS box. The server (based on Postfix) does reverse DNS checks as an anti-spam measure, and checking the mailogs recently when I was suspicious of some expected mail not arriving I'm getting entries with failed DNS lookup like this...
Oct 22 15:24:11 server postfix/smtpd[12267]: warning: hostname lux.smtp-out.eu-west-1.amazonses.com does not resolve to address 176.32.127.137: Name or service not known
Oct 22 15:24:11 server postfix/smtpd[12267]: connect from unknown[176.32.127.137]
Oct 22 15:24:11 server postfix/smtpd[12267]: lost connection after CONNECT from unknown[176.32.127.137]
Oct 22 15:24:11 server postfix/smtpd[12267]: disconnect from unknown[176.32.127.137]
In this particular case I'm missing some expected mail from Amazon.
On my LAN, on any box, if I run nslookup on the hostname, it just sits there and then times out...
nslookup lux.smtp-out.eu-west-1.amazonses.com
Server: dsldevice.lan
Address: 192.168.1.254
*** dsldevice.lan can't find lux.smtp-out.eu-west-1.amazonses.com: Unspecified error
If however I explicitly specify a plusnet DNS server in nslookup, it resolves fine.
e.g.
nslookup lux.smtp-out.eu-west-1.amazonses.com 212.159.13.49
Server: cdns01.plus.net
Address: 212.159.13.49
Non-authoritative answer:
Name: lux.smtp-out.eu-west-1.amazonses.com
Addresses: 176.32.127.200
176.32.127.203
176.32.127.201
176.32.127.137
176.32.127.202
176.32.127.139
176.32.127.205
176.32.127.138
176.32.127.140
176.32.127.204
176.32.127.136
176.32.127.141
176.32.127.143
176.32.127.206
176.32.127.142
176.32.127.207
Looking at the router, the DNS servers are 212.159.6.10 & 212.159.6.9
If I manually nslookup with these, again it resolves fine.
Then more oddly, if I log into the router CLI and nslookup from there, it also works fine...
{admin}=>dns client nslookup
host = lux.smtp-out.eu-west-1.amazonses.com
:dns client nslookup host=lux.smtp-out.eu-west-1.amazonses.com
Name: lux.smtp-out.eu-west-1.amazonses.com
Address: 176.32.127.139
Type: IP
176.32.127.205
Type: IP
176.32.127.137
Type: IP
176.32.127.202
Type: IP
176.32.127.203
Type: IP
176.32.127.201
Type: IP
176.32.127.200
Type: IP
176.32.127.138
Type: IP
176.32.127.141
Type: IP
176.32.127.136
Type: IP
176.32.127.204
Type: IP
176.32.127.140
Type: IP
176.32.127.207
Type: IP
176.32.127.142
Type: IP
176.32.127.206
Type: IP
176.32.127.143
Type: IP
Aliases: none
It only affects some addresses though. Vast majority of mail is getting through and reverse DNS is working. I don't really notice issues resolving hosts when browsing. It's just the odd few mail servers.
Any ideas? Maybe it's not the router, but then the router is the only device serving DNS for the LAN and all boxes on my LAN are configured automatically with the router IP address as DNS server (192.168.1.254) and all fail with the above hostname and a few others that should work.
Re: Technicolor TG582n FTTC DNS resolution issues?
24-10-2015 4:18 PM
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The DNS answer for lux.smtp-out.eu-west-1.amazonses.com from Plusnet DNS is 575 bytes, so I was wondering if that has exceeded a packet size limit somewhere. Of course, if other hostnames that don't resolve have much shorter answers, then the packet size won't be the problem. The dig command line utility, or wireshark, can be used to see the length of the DNS answer data received.
Google DNS sent a shorter answer, Plusnet DNS sent 16 IP addresses and the details of 10 authoritative nameservers, Google DNS just sent the 16 IP addresses, and didn't send the additional details of the authoritative nameservers.
Re: Technicolor TG582n FTTC DNS resolution issues?
24-10-2015 5:54 PM
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Ran a few scripts to test them out and found another example that should resolve though (although still this could be a spammer. Some Polish university it seems).
1lo.vlan327.nemes.lubman.net.pl - resolves to a long list of IP addresses, one of which is the one the mail server claims doesn't resolve, and if I just to nslookup on it, it times out, but nslookup explicitly against a PN DNS server and it does resolve and one of the IP addresses matches the one it claimed to be in the mail server log. The long list would also suggest an issue with large packet?
Re: Technicolor TG582n FTTC DNS resolution issues?
24-10-2015 6:19 PM
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I only thought of the length issue because I happened to test the DNS server in my really old netgear router (I don't normally use its DNS server). That couldn't properly handle the first example, and truncated the DNS reply data to 512 bytes. But the TG582n is not so old, and should be expected to work, or might eventually get a firmware update to fix this if we can confirm it and Plusnet report it to Technicolor.
Perhaps you could check the 582n system log, to see if there are any firewall or IDS log messages to suggest either of those components are somehow blocking the packets. The fact that the telnet cli on the router does resolve these hostnames, but your computers do not, suggests that parts of the DNS system in the firmware can handle these packets, yet somehow the answers don't get sent to or don't reach your computers.
Re: Technicolor TG582n FTTC DNS resolution issues?
24-10-2015 6:23 PM
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Edit: checked the logs from the router (I've got them sending to my Synology log server) and there's nothing around these times. Syslog is set to 'info' level which is logging all except 'debug' level logs it seems.
Re: Technicolor TG582n FTTC DNS resolution issues?
24-10-2015 6:40 PM
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Or perhaps anyone else using a 582n with 10.2 firmware, with default DNS configuration, could test looking up either of the hostnames mentioned to check if it works.
Re: Technicolor TG582n FTTC DNS resolution issues?
24-10-2015 10:47 PM
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Quote C:\Users\npr>dig lux.smtp-out.eu-west-1.amazonses.com @127.0.0.1
;; Truncated, retrying in TCP mode.
;; Connection to 127.0.0.1#53(127.0.0.1) for lux.smtp-out.eu-west-1.amazonses.com failed: connection refused.
Increase the buffer size from the default 512 to 1024
Quote ; <<>> DiG 9.8.6-P1 <<>> +bufsize=1024 lux.smtp-out.eu-west-1.amazonses.com @127.0.0.1
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 3981
;; flags: qr rd ra; QUERY: 1, ANSWER: 16, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;lux.smtp-out.eu-west-1.amazonses.com. IN A
;; ANSWER SECTION:
lux.smtp-out.eu-west-1.amazonses.com. 765 IN A 176.32.127.138
lux.smtp-out.eu-west-1.amazonses.com. 765 IN A 176.32.127.140
lux.smtp-out.eu-west-1.amazonses.com. 765 IN A 176.32.127.143
lux.smtp-out.eu-west-1.amazonses.com. 765 IN A 176.32.127.136
lux.smtp-out.eu-west-1.amazonses.com. 765 IN A 176.32.127.139
lux.smtp-out.eu-west-1.amazonses.com. 765 IN A 176.32.127.205
lux.smtp-out.eu-west-1.amazonses.com. 765 IN A 176.32.127.137
lux.smtp-out.eu-west-1.amazonses.com. 765 IN A 176.32.127.202
lux.smtp-out.eu-west-1.amazonses.com. 765 IN A 176.32.127.142
lux.smtp-out.eu-west-1.amazonses.com. 765 IN A 176.32.127.141
lux.smtp-out.eu-west-1.amazonses.com. 765 IN A 176.32.127.207
lux.smtp-out.eu-west-1.amazonses.com. 765 IN A 176.32.127.201
lux.smtp-out.eu-west-1.amazonses.com. 765 IN A 176.32.127.206
lux.smtp-out.eu-west-1.amazonses.com. 765 IN A 176.32.127.203
lux.smtp-out.eu-west-1.amazonses.com. 765 IN A 176.32.127.204
lux.smtp-out.eu-west-1.amazonses.com. 765 IN A 176.32.127.200
;; Query time: 15 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Sat Oct 24 22:27:20 GMT Summer Time 2015
;; MSG SIZE rcvd: 321
Strangely querying 8.8.8.8 works without increasing the buffer size yet gives the same answer size.
Correction: google dns gives a message size of 310.
Re: Technicolor TG582n FTTC DNS resolution issues?
29-11-2015 5:55 PM
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Oh hang on again, doing some googling for people having problems with failed DNS lookups on Windows 8/8.1 reveals that there are other non-Technicolor routers with similar problems. I wonder what the common factors are here, apart from Windows. Do they use similar hardware, do they all have a common firmware bug - does this buffer size theory hold any water? I don't know, I'm just asking questions.
And btw the 582n's with 10.2. firmware still have occasional DNS lookup failures but then it's not the only router I've used that seems to have that occasional problem.
Re: Technicolor TG582n FTTC DNS resolution issues?
29-11-2015 6:32 PM
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Re: Technicolor TG582n FTTC DNS resolution issues?
29-11-2015 7:19 PM
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Re: Technicolor TG582n FTTC DNS resolution issues?
29-11-2015 7:27 PM
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Re: Technicolor TG582n FTTC DNS resolution issues?
29-11-2015 8:44 PM
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Re: Technicolor TG582n FTTC DNS resolution issues?
29-11-2015 9:09 PM
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But I guess I shouldn't bother posting any links to anything, because no-one clicks them and reads them? I should've just said that I've searched the Internet, and it turns out there is indeed a bug in the Technicolor firmware.
Re: Technicolor TG582n FTTC DNS resolution issues?
30-11-2015 9:57 AM
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Re: Technicolor TG582n FTTC DNS resolution issues?
30-11-2015 10:10 AM
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