Cisco Pix drops UDP packets larger than 512 bytes
Pete Ehlke
pde at ehlke.net
Mon Jun 3 19:24:01 UTC 2002
On Mon, Jun 03, 2002 at 12:25:08PM -0700, Jean-Christophe Smith wrote:
>
> RFC 1035
>
> ---------------------------------------------------
> 2.3.4. Size limits
>
> Various objects and parameters in the DNS have size limits. They are
> listed below. Some could be easily changed, others are more
> fundamental.
>
> labels 63 octets or less
>
> names 255 octets or less
>
> TTL positive values of a signed 32 bit number.
>
> UDP messages 512 octets or less
>
> ---------------------------------------------------
> 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.
>
I'd suggest that you spend some time reading the various RFCs related to
EDNS0. 512 is no longer a mandatory datagram size limit.
-Pete
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