Re: Firewall question

From: Wayne McGlinn (wmcglinn@optushome.com.au)
Date: 03/15/03 

From: "Wayne McGlinn" <wmcglinn@optushome.com.au>
Date: Sun, 16 Mar 2003 00:43:36 +1000

References please ?? Not Cisco, but RFC's if possible :) As I quoted
previously from STD13:

"4.2.1. UDP usage

Messages sent using UDP user server port 53 (decimal).

Messages carried by UDP are restricted to 512 bytes (not counting the IP
or UDP headers). Longer messages are truncated and the TC bit is set in
the header.

UDP is not acceptable for zone transfers, but is the recommended method
for standard queries in the Internet. Queries sent using UDP may be
lost, and hence a retransmission strategy is required. Queries or their
responses may be reordered by the network, or by processing in name
servers, so resolvers should not depend on them being returned in order."

Wayne

"Jesper Skriver" <harvest@wheel.dk> wrote in message
news:slrnb76ehs.16vh.harvest@freesbee.wheel.dk...
> On Sat, 15 Mar 2003 14:26:57 -0000, Chris wrote:
>
> > I agree. TCP 53 is only used for zone transfers between DNS servers,
> > not DNS lookups.
>
> Not correct, lookup's will fallback to TCP if the reply cannot fit a
> single UDP packet.
>
> > Besides, the mail server in question will only need to query MX
> > records when sending out mail if not using a smart host. UDP 53 is all
> > it needs.
>
> See above.
>
> --
> Jesper Skriver, CCIE #5456
> FreeBSD committer

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