Cisco Pix drops UDP packets larger than 512 bytes

[Pete Ehlke]

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