[CentOS] Centos 5.4 DNS resolution issue

John R Pierce pierce at hogranch.com
Mon Mar 8 05:49:36 UTC 2010


Gaurav Nangla wrote:
> I can ping the google.com <http://google.com> ip addresses 
> (209.85.231.104) but can't ping the FQDN, obviously DNS is broken.
>
> I can also ping the nameserver ip addresses specified in /etc/resolv.conf.

well, the DNS servers given by your resolv.conf output seem valid from 
here..  I recommend doing some more debugging with `host` or similar DNS 
diagnostic tools.

note regular DNS lookups like these tend to use UDP rather than TCP, if 
you're behind a NAT firewall which doesn't allow outbound udp port 53 
and connection track the response, then things might not work well.


$ host google.com 208.67.220.220
Using domain server:
Name: 208.67.220.220
Address: 208.67.220.220#53
Aliases:

google.com has address 74.125.19.105
google.com has address 74.125.19.99
google.com has address 74.125.19.103
google.com has address 74.125.19.106
google.com has address 74.125.19.147
google.com has address 74.125.19.104
google.com mail is handled by 400 google.com.s9b2.psmtp.com.
google.com mail is handled by 200 google.com.s9a2.psmtp.com.
google.com mail is handled by 300 google.com.s9b1.psmtp.com.
google.com mail is handled by 100 google.com.s9a1.psmtp.com.

$ host google.com 208.67.222.222
Using domain server:
Name: 208.67.222.222
Address: 208.67.222.222#53
Aliases:

google.com has address 74.125.19.105
google.com has address 74.125.19.147
google.com has address 74.125.19.99
google.com has address 74.125.19.103
google.com has address 74.125.19.104
google.com has address 74.125.19.106
google.com mail is handled by 400 google.com.s9b2.psmtp.com.
google.com mail is handled by 200 google.com.s9a2.psmtp.com.
google.com mail is handled by 300 google.com.s9b1.psmtp.com.
google.com mail is handled by 100 google.com.s9a1.psmtp.com.


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