Priscilla Oppenheimer wrote:
>
> Thanks for the info. I was just getting sick of all the misinformation so I
> over-simplified a bit and optimized for the most usual case. I was glad to
> get your response, though, since you obviously have the Authoritative
> Answer bit set! &;-)
:) I am by no means the authority on this... just trying to help (just
like you :-)
> So, why would a DNS query generate a response that would be larger than 500
> bytes, though?? I am aware of the Truncation bit in the DNS header, but
> have never seen it set. Just trying to learn. Thanks.
>
> Priscilla
Most of the times the DNS query responses will not exceed the 512 bytes
or so. I guess this "rollover to TCP" was put in place as a
precaution. When troubleshooting, one might want query a domain with
the "set q=any" option. This returns lots of information about the
domain which might (depending on the domain) push it over the UDP
payload limit.
Whether to use TCP DNS queuries is up to the requester. Some clients
prefer the connection oriented approach... this is the case with Cisco's
Distributed Director, which uses TCP DNS queries as a way of testing
response times. You could also force a TCP query by using the vc
option.
I'll include this link on my web server for those who are interested in
deeper reading into DNS.... enjoy :-).
http://www.ietf.org/rfc/rfc1034.txt?number=1034
http://www.ietf.org/rfc/rfc1035.txt?number=1035
mark
_________________________________
FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
