Network troubleshooting, any experts?
Jeff Vian
jvian10 at charter.net
Wed Apr 28 23:08:29 UTC 2004
Elam Daly wrote:
> gforte wrote:
>
>> With all (un)due respect, your ISP is probably full of crap. Your
>> tcpdumps
>> indicate that your UDP connections to the DNS servers are getting
>> through,
>> at the least. That's why you're able to resolve hostnames. The fact
>> that
>> your TCP syns never get responded to suggest that they are being blocked
>> someplace. If the server is not running any firewall as you say,
>> then the
>> only other logical place is at the border router.
>>
>> -g
>
>
>
> Does DNS resolve names through UDP? Would that explain why I can't
> telnet
> to port 53 on the DNS servers,yet still get name resolutions? Am I
> wrong conceptually
> on how DNS works?
> Thanks
> Elam
>
YES, and YES
DNS service uses UDP,
Telnet is TCP
However, there still appears to be a TCP block. If you look at
/etc/services you see port 53 is defined as domain for both TCP and UDP.
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