ping: unknown host google.com

Question

Relevant output:

/etc/hosts
127.0.0.1               localhost localhost.localdomain localhost4  localhost4.localdomain4
::1             localhost localhost.localdomain localhost6 localhost6.localdomain6
servers_ip_address            server.2006scape.com server


/etc/resolv.conf
search 2006scape.com
#Generated by NetworkManager
nameserver 8.8.8.8
nameserver 8.8.4.4

Some stuff from tcpdump

07:46:28.795843 IP server_ip.42841 > 8.8.4.4.domain: 60253+ PTR? 87.127.104.87.in-addr.arpa. (44)
07:46:28.795980 IP server_ip.54001 > 8.8.4.4.domain: 7390+ PTR? 60.187.80.98.in-addr.arpa. (43)
07:46:28.804029 IP server_ip.59667 > 8.8.4.4.domain: 58876+ PTR? 134.154.161.72.in-addr.arpa. (45)
07:46:28.884171 IP server_ip.46255 > 8.8.4.4.domain: 63027+ PTR? 195.156.251.84.in-addr.arpa. (45)
07:46:28.884217 IP server_ip.35426 > 8.8.4.4.domain: 10538+ PTR? 118.3.182.166.in-addr.arpa. (44)
07:46:28.884253 IP server_ip.53635 > 8.8.4.4.domain: 29928+ PTR? 230.94.81.83.in-addr.arpa. (43)
07:46:28.884286 IP server_ip.45787 > 8.8.4.4.domain: 41151+ PTR? 18.32.223.121.in-addr.arpa. (44)
07:46:28.946045 IP server_ip.47246 > 8.8.4.4.domain: 43103+ PTR? 81.70.251.84.in-addr.arpa. (43)
07:46:28.946066 IP server_ip.33208 > 8.8.4.4.domain: 61117+ PTR? 69.170.184.71.in-addr.arpa. (44)

Anyone have any input as to what is causing this?

Can you paste the command you're running and the exact response. — EightBitTony, Jun 11 '12 at 12:57
-1: This question is poorly worded and doesn't explain the actual problem is. I'd edit it myself to correct, but I can't really figure it out enough to even do that. I'll remove the minus one once the question is corrected to be clear enough to determine what it is actually asking. — Jed Daniels, Jun 11 '12 at 14:29

score 3 · Answer 1 · answered Jun 11 '12 at 13:32

3

I'm only seeing one-way traffic in that tcpdump, no responses. Did you specify only outbound DNS requests (say, dst port 53) or are you not getting any responses?

Can you make any DNS requests at all? (Use dig to test this.)

answered Jun 11 '12 at 13:32

Ladadadada

26,337
7
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dig and nslookup always fail to connect to host no matter what arguments I use. this is the tcpdump command i used: `tcpdump -n not port ssh and not port 4838 and not port 80 and not port 6667` I have stopped iptables, restarted and made sure port 53 was allowed etc. I can ping all IP addresses fine but no domains resolve. – Tar Jun 11 '12 at 13:45
Do you have a hardware firewall or does your hosting provider run one for you? That's what I'm leaning towards for the cause of this. Does your hosting provider also provide DNS servers? They might block DNS requests to any other DNS provider. Also, can you ping `8.8.8.8` and `8.8.4.4`? – Ladadadada Jun 11 '12 at 13:50
Yes, I can ping them. It's weird because I've been using google DNS ever since we switched to this server like 2 months ago with no problems. I emailed them and asked about a default DNS server. My host does have a hardware firewall but I can't imagine why it would start happening just now. – Tar Jun 11 '12 at 13:57

Vic Abreu · Answer 2 · 2012-06-11T14:19:14.150

0

I have two servers running Debian Squeeze with this configuration and everything if fine without using nslookup google.com.

/etc/resolv.conf
  nameserver 8.8.8.8
  nameserver 8.8.4.4

Maybe you forgot to set a correct route.

edited Jun 11 '12 at 14:19

answered Jun 11 '12 at 13:31

Vic Abreu

111
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Here is the output of `route -n` server_ip 0.0.0.0 255.255.255.0 U 0 0 0 em1 169.254.0.0 0.0.0.0 255.255.0.0 U 1002 0 0 em1 0.0.0.0 server_ip 0.0.0.0 UG 0 0 0 em1 – Tar Jun 11 '12 at 13:43

score 0 · Answer 3 · answered Jun 11 '12 at 15:19

0

It is a problem reaching your DNS server or with return DNS packets. You can start debugging by running traceroute on the port 53/UDP:

traceroute -np 53 8.8.8.8

This will show if it is your local firewall or a remote problem.

answered Jun 11 '12 at 15:19

Mircea Vutcovici

17,619
4
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ping: unknown host google.com

3 Answers3