RE: how smart is the state engine?

[Sneppe Filip]

Title: RE: how smart is the state engine?

[EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]

>>On Thu, May 16, 2002 at 02:11:33PM -0400, Ramin Alidousti wrote:
>>
>> When does a UDP DNS query result in a TCP response? DNS doesn't work that
>> way. See rfc1035.
>
>I believe it does in the case of *large* responses:
>
>http://www.acmebw.com/askmrdns/archive.php?category=81&question=189
>

I believe Ramin wasn't actually expecting an answer to his question :-)
It should actually be taken as a statement.

One cannot simply send a UDP packet and expect a tcp packet in return,
since tcp require a packet exchange of three packets before any actual
data goes over it. So what happen in reality is that the client sends
a udp packet, either gets a response to use tcp or gets no response
at all; in both cases the client is supposed to revert to tcp for
the DNS lookup, and this means going through the SYN, SYN+ACK, ACK
3-way handshake first.

As you can see, a firewall will not have any problems with this type of
packet exchange.

Regards,
Filip