EDNS in DNS clients

[Stefan Puiu]

Quoting from RFC 1035:=20
-----
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
---=20

Nothing about the maximum query size. Now, the DNS header is 6*16 bits
=3D 12 bytes long, plus 2 bytes for the query type and other two for the
query class, that makes 16 bytes excluding the QNAME, which itself can
be 255 bytes long (unless I'm missing something), so that would be 271
bytes, I suppose. On the other hand, notice that you need one quite
long domain name to fill or go over those 255 bytes. Definitely
possible, but not too practical.

On 5/23/05, Stephane Bortzmeyer <bortzmeyer at nic.fr> wrote:
> On Mon, May 23, 2005 at 05:12:04PM +0300,
>  Stefan Puiu <stefan.puiu at gmail.com> wrote
>  a message of 22 lines which said:
>=20
> > As it says, this is for queries of 255 bytes, which I think is quite
> > large.
>=20
> It is the maximum authorized by the protocol (RFC 1035, 2.3.4. Size
> limits) so it is *possible*.
>=20
>