DNS problems

[Chris Edwards]

Currently getting no DNS response from 194.168.4.100 :(

Whereas 194.168.8.100 is working fine.

This in Glasgow / renf / canniesburn area.



chris-macbook> dig @194.168.4.100 www.bbc.co.uk
; <<>> DiG 9.4.3-P1 <<>> @194.168.4.100
; (1 server found)
;; global options: printcmd
;; connection timed out; no servers could be reached




chris-macbook> dig @194.168.8.100 www.bbc.co.uk
; <<>> DiG 9.4.3-P1 <<>> @194.168.8.100 www.bbc.co.uk
; (1 server found)
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 36804
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;www.bbc.co.uk. IN A

;; ANSWER SECTION:
www.bbc.co.uk. 69 IN CNAME www.bbc.net.uk.
www.bbc.net.uk. 236 IN A 212.58.251.195

[moaningmags]

Microsoft Windows [Version 6.0.6001]
Copyright (c) 2006 Microsoft Corporation. All rights reserved.

C:\Users\Mum>ping 194.168.4.100

Pinging 194.168.4.100 with 32 bytes of data:
Reply from 194.168.4.100: bytes=32 time=11ms TTL=251
Reply from 194.168.4.100: bytes=32 time=8ms TTL=251
Reply from 194.168.4.100: bytes=32 time=7ms TTL=251
Reply from 194.168.4.100: bytes=32 time=9ms TTL=251

Ping statistics for 194.168.4.100:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 7ms, Maximum = 11ms, Average = 8ms

Name: cache1.service.virginmedia.net
Address: 194.168.4.100



Working fine here in Uddingston.

[Chris Edwards]

Hi,

Interestingly I can "ping" 194.168.4.100 OK, but it doesn't answer actual DNS queries

(ie. the resolving service on udp port 53).

Unfortunately I've forgotten the PC command to check this. Maybe "nslookup" is available, as in:


nslookup
server 194.168.4.100
www.bbc.co.uk (times out)

server 194.168.8.100
www.bbc.co.uk (gives answer)

[xocemp]

xocemp@ZeN ~> nslookup 194.168.4.100
Server: 192.168.1.254
Address: 192.168.1.254#53

Non-authoritative answer:
100.4.168.194.in-addr.arpa name = cache1.service.virginmedia.net.

Authoritative answers can be found from:
4.168.194.in-addr.arpa nameserver = ns4.virginmedia.net.
4.168.194.in-addr.arpa nameserver = ns1.virginmedia.net.
4.168.194.in-addr.arpa nameserver = ns2.virginmedia.net.
4.168.194.in-addr.arpa nameserver = ns3.virginmedia.net.
ns1.virginmedia.net internet address = 62.253.162.237
ns2.virginmedia.net internet address = 194.168.4.237
ns3.virginmedia.net internet address = 62.253.162.37
ns4.virginmedia.net internet address = 194.168.4.33

xocemp@ZeN ~>

[moaningmags]

Microsoft Windows [Version 6.0.6001]
Copyright (c) 2006 Microsoft Corporation. All rights reserved.

C:\Users\Mum>nslookup
Default Server: UnKnown
Address: 192.168.1.1

> 194.168.4.100
Server: UnKnown
Address: 192.168.1.1

Name: cache1.service.virginmedia.net
Address: 194.168.4.100

Is what I get doing nslookup.

> server 194.168.4.100
Default Server: cache1.service.virginmedia.net
Address: 194.168.4.100

> server 194.168.8.100
Default Server: cache2.service.virginmedia.net
Address: 194.168.8.100

>

[Chris Edwards]

Hi xocemp,

Looks like you asked some other DNS server (not sure which, but it seems to have address 192.168.1.254 on your network) for the name corresponding to number 194.168.4.100. This isn't necessarily the same as asking 194.168.4.100 itself a question. The relevant test would be to set the server explicitly, and then ask something - for example:


nslookup

server 194.168.4.100
www.bbc.co.uk (fails)

server 194.168.8.100
www.bbc.co.uk (works)



Hi moaningmags,

To test with nslookup, want to set the server explicitly, then type a name to look up e.g "www.bbc.co.uk", as in the example above.

Thanks anyways folks :)

[moaningmags]

C:\Users\Mum>nslookup
Default Server: UnKnown
Address: 192.168.1.1

> server 194.168.4.100
Default Server: cache1.service.virginmedia.net
Address: 194.168.4.100

> www.bbc.co.uk
Server: cache1.service.virginmedia.net
Address: 194.168.4.100

Non-authoritative answer:
Name: www.bbc.net.uk
Address: 212.58.251.195
Aliases: www.bbc.co.uk

Like that?

[nicolodeon]

Chris

Of course you could switch to opendns until resolved.

208.67.222.222
208.67.220.220

Cheers

[Chris Edwards]

Like that?

Thanks for this.

Yep - exactly like that. Looks like it's fully OK for you.

Interesting!

I have a feeling VM may use cunning trickery known as "Anycast (http://en.wikipedia.org/wiki/Anycast)" for the resolving DNS service. That is, multiple physical servers, at different locations, provide the service for each of the two published DNS addresses. But I'd be a little surprised if they have enough servers such that customers in different parts of a city get different instances (which is kinda what it looks like...)

Then again, trying traceroute (spelt "tracert" on Windows I think) kinda suggests I'm getting a (failed?) instance of 194.168.4.100 located right in my area ("renf"), whereas 194.168.8.100 may, for me, correspond to something much further away, in the "win" area, wherever that is.

This anycast stuff is pure guesswork, and could be complete rubbish ;)



chris-macbook> traceroute 194.168.4.100
traceroute to 194.168.4.100 (194.168.4.100), 64 hops max, 40 byte packets
1 10.232.112.1 (10.232.112.1) 8.575 ms 8.227 ms 18.930 ms
2 renf-cam-1b-v129.network.virginmedia.net (80.4.65.125) 9.200 ms 8.508 ms 8.273 ms
3 renf-core-1b-ae1-0.network.virginmedia.net (195.182.176.177) 17.778 ms 9.064 ms 10.155 ms
4 cache1.service.virginmedia.net (194.168.4.100) 7.958 ms 10.762 ms 10.719 ms


chris-macbook>traceroute 194.168.8.100
traceroute to 194.168.8.100 (194.168.8.100), 64 hops max, 40 byte packets
1 10.232.112.1 (10.232.112.1) 8.004 ms 8.158 ms 8.349 ms
2 renf-cam-1b-v129.network.virginmedia.net (80.4.65.125) 8.062 ms 7.879 ms 8.571 ms
3 renf-core-1b-ae2-0.network.virginmedia.net (195.182.176.181) 11.193 ms 18.623 ms 32.455 ms
4 lee-bb-b-as3-0.network.virginmedia.net (213.105.175.225) 36.498 ms 15.551 ms 34.719 ms
5 pop-bb-a-as1-0.network.virginmedia.net (213.105.175.130) 22.258 ms 34.556 ms 18.648 ms
6 win-bb-b-ae1-0.network.virginmedia.net (62.253.185.202) 20.471 ms 22.537 ms 20.001 ms
7 win-dc-b-v900.network.virginmedia.net (62.253.188.166) 20.099 ms 23.969 ms 24.443 ms
8 winn-dnssw-1b-v851.network.virginmedia.net (62.253.181.12) 23.107 ms 22.525 ms 21.478 ms
9 cache2.service.virginmedia.net (194.168.8.100) 23.396 ms * 22.203 ms


---------- Post added at 02:36 ---------- Previous post was at 02:31 ----------

Of course you could switch to opendns until resolved.

Yep.

And everyone who's computer has both VM DNS addresses should be OK, as lookups should fall back to the 2nd ".8" one, which is working fine here. Unfortunately however, this can result in several-second delays for various activities, such as browsing. Here, I've swapped the order, which has sorted things, tho I'd wager other folk nearby will be experiencing said delays.

[Chris Edwards]

Fixed now - both VM addresses responding again.