ipfw confusion

[Gary Aitken]

On 08/19/13 00:36, Jason Cox wrote:
> Are you sure that your DNS requests are over TCP? DNS primarily uses UDP to
> serve requests. TCP is used when the response data size exceeds 512 bytes
> (I think), or for tasks such as zone transfers. I know a few resolver
> implementations use TCP for all queries, but most I have used not. You
> might want to add rules to allow UDP as well.

There are identical rules included for udp:

21149 allow udp from any to 12.32.44.142 dst-port 53 in via tun0 keep-state
21169 allow udp from any to 12.32.36.65 dst-port 53 in via tun0 keep-state

One of the requests which is being refused is a zone transfer request from 
a secondary which is a tcp request.  Others are probably udp.

> On Sun, Aug 18, 2013 at 11:06 PM, Gary Aitken <vagabond at blackfoot.net>wrote:
> 
>> I'm having some weird ipfw behavior, or it seems weird to me, and am
>> looking
>> for an explaination and then a way out.
>>
>> ipfw list
>> ...
>> 21109 allow tcp from any to 12.32.44.142 dst-port 53 in via tun0 setup
>> keep-state
>> 21129 allow tcp from any to 12.32.36.65 dst-port 53 in via tun0 setup
>> keep-state
>> ...
>> 65534 deny log logamount 5 ip from any to any
>>
>> tail -f messages
>> Aug 18 23:33:06 nightmare named[914]: client 188.231.152.46#63877: error
>> sending response: permission denied
>>
>> 12.32.36.65 is the addr of the internal interface (xl0) on the firewall
>>   and is the public dns server.
>> 12.32.44.142 is the addr of the external interface (tun0) which is bridged
>> on a
>> dsl line.
>>
>> It appears that a dns request was allowed in, but the response was not
>> allowed
>> back out.  It seems to me the above rules 21109 and 21129 should have
>> allowed
>> the request in and the response back out.
>>
>> It's possible a request could come in on 12.32.44.142,
>> which is why 21109 is present;
>> although I know I am getting failures to reply to refresh requests
>> from a secondary addressed to 12.32.36.65
>>
>> What am I missing?
>>
>> Is there a problem if the incoming rule is for tun0,
>> which gets passed to named
>> since 12.32.44.142 is on the physical machine running named,
>> but named pumps its response out on 12.32.36.65,
>> relying on routing to get it to the right place,
>> and that fails to match the state tracking mechanism
>> which started with 12.32.44.142?
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> 
> 
>