From: James Couzens
Sent: Friday, April 16, 2004 9:30 PM
On Thu, 2004-04-15 at 04:56, Stefan Engelbert wrote:
I was wondering if SPF could be used by Domain owners which dont have
access to to their DNS Servers.
It could. In fact, its a pretty cool idea. I'm all for anything that
would help further SPF deployment. However, there is an obscene amount
of overhead in using TCP, (40 bytes as opposed to UDP's 28) in addition
you must also factor in HTTP overhead, as well as dealing with the fact
that TCP has to negotiate to establish a connection, where as UDP is
fire and forget.
<...>
HTTP (TCP):
-----------
Packet count: 10
Bytes of traffic: 1191
DNS (UDP):
----------
Packet count: 2
Bytes of traffic: 132
1191/132 = 9.02 or 9x more data than a DNS query.
To amplify what James is saying, I bet the numbers he gave are when the TCP
transaction occurs without any errors. Since TCP has extensive error
recovery mechanisms, which also makes the protocol stack code much larger
and slower, the CPU and network bandwidth penalties can probably get a lot
worse when an error occurs. OTOH, UDP does not guarantee error-free
delivery so you either just re-request the data or time out and decide what
to do next.
--
Seth Goodman