Inconsistent DNS availability

Richard Russell richard at
Wed May 7 14:16:50 CST 2003

John Edwards writes: 

> Hi Richard, 
> Are you blocking port 53 TCP on a firewall, while allow port 53 UDP in?

7348  510K ACCEPT     udp  --  any    any     anywhere             anywhere  
udp dpt:domain
   7   368 ACCEPT     tcp  --  any    any     anywhere             anywhere  
tcp dpt:domain

> Directly querying for what you want generates a 499 byte reply because the 
> name servers have enough NS records to survive several 
> simultaneous apocalypses, whereas querying the caching nameservers of Adam 
> will only net you a condensed 110 bytes. 499 bytes is not enough to 
> require TCP in the DNS response, but it might give you a hint as to where 
> to look.

Hmm... Umm... Nope... 

> Do you have any interfaces or aliases on your system that might have an IP 
> address that is part of the university network?

I have a 192.168 which is not snat'd, only http proxied, though there is a 
dns server there somewhere (I'd just have to find it)

> To get around your problem quickly, does it work if you simply put Adam's 
> DNS servers in /etc/resolv.conf, remove, and restart the mail 
> queue?

Indeed it did... though it was remarkably slow in doing so... 

Cheers for that -- though it doesnt' tell me why it happnenned in the first 
place... :S ... :) 


Richard Russell
Yellow Goanna P/L
m: +61 412 827 805
e: richard at

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