What is the sense of telnet on 53 port?

[Kevin Darcy]

kily at my-deja.com wrote: FQDN my be any domaine on the net prove

> -In recent versions of Bind where DNSSEC and  IXFR, DDNS, Notify,
> EDNSO protocoles are included, is this means that TCP must be used
> instead of UDP even for a simples request of addresses resolutions?

DDNS packets aren't really "queries" in the normal sense. The client constructs the
update and sends it to the server. So the client will know ahead of time whether the
data will be too much to fit in a UDP packet or not, and use TCP if necessary.
DDNS responses are basically just confirmations or rejections, so they tend to be
rather small and are unlikely to require TCP.

IXFR is a way of doing zone transfers, and zone transfers traditionally use
TCP anyway, so IXFR can hardly be said to be forcing the use of TCP. If an
IXFR transfer will fit in a UDP packet, then in theory UDP can be used. That's a
choice you never had with AXFR.

NOTIFY packets are small. I can't imagine them ever needing to use TCP.

EDNS0 adds a little to the packet length, true. But EDNS0 also allows clients and
servers to use larger UDP packets too, so it more than "pays its way" as far as
reducing TCP retransmissions.

DNSSEC is the remaining protocol extension you mentioned, and yes, it can increase
packet size considerably. It is hoped that the buffer-size advertisement feature of
EDNS0 will help offset the impact of this somewhat by allowing larger UDP packets.
We'll see.


- Kevin