On 08/23/2000 at 23:17:50 EST, Frank Knobbe <[EMAIL PROTECTED]> wrote:
> > The other is even more obvious. Most, if not all, telnet clients
> > will attempt to perform telnet option negotiation at the beginning
> > of a connection. [...]
>
> True, except Netcat does not do this unless you tell it to.
Netcat isn't what I would term a telnet client. Of course it is possible
to postulate or write a tcp application that can have any behavior you
like, but this thread was referring to telnet apps talking to smtp mail
servers.
> One last note, though. SMTP email originates on port 25.
No smtp app that I've seen does this. Here is the first packet of Aix
sendmail connecting to an smtp server - check the source port:
IP header breakdown:
< SRC = 9.1.40.50 > (sk2.almaden.ibm.com)
< DST = 9.1.10.30 > (k85b.almaden.ibm.com)
ip_v=4, ip_hl=20, ip_tos=0, ip_len=44, ip_id=14947, ip_off=0
ip_ttl=59, ip_sum=118, ip_p = 6 (TCP)
TCP header breakdown:
<source port=3801, destination port=25(smtp) >
th_seq=dd1cf201, th_ack=0
th_off=6, flags<SYN>
th_win=16384, th_sum=35c4, th_urp=0
mss 1460
Tony Rall
-
[To unsubscribe, send mail to [EMAIL PROTECTED] with
"unsubscribe firewalls" in the body of the message.]
