[ale] Network Problem

[Jacob Langseth]

> I installed Redhat 5.0 in an IBM Thinkpad 760XL.  I have a 3com 3c589d
> PCMCIA card.  The card works under Win95.  After booting up Linux, the card
> registers fine.  I can ping all three machines from the laptop.  I can
> nslookup from the laptop, connect to the DNS server and query all I want.
> I can ping from all three machines to the laptop with no problem.  This
> leads me to believe that the network is setup correctly.

don't know if this will help or not, but your problem seems
to manifest only when tcp is involved.  ping is icmp, nslookup /
dns queries are udp, but when you telnet, ftp, or nfs (all tcp)
it hangs.

I don't know how much this will help you, but it's definitely
interesting.

> see it the IP address it tries to connect to.  Eventually the telnet will
> time out.  On either the 486 or pentium, I get the following message in
> /var/log/secure:
> 
> May 29 23:25:37 cimmeria in.telnetd[715]: warning: can't get client
> address:  Connection timed out
> May 29 23:25:37 cimmeria in.telnetd[715]: refused connect from unknown.

Try running tcpdump on one of your other linux systems during
the connect, and take a look to see where it dies.

I've seen logs similiar to the above generated from fast port
scanning and half-open scans, as accept() under linux returns
after the first syn of the three way handshake.  Taking a guess,
it seems like the thinkpad may not be making it to the final ack.
Tcpdump should let you know for sure.

> I get no such message on the sparc.

If I'm correct that linux's accept() is unique in the way it
returns after the syn, this seems to confirm that the
handshake isn't completing.

> Does anybody have any suggestions?

Look at tcpdump, find out if it is specific to the tcp handshake,
and if it is, forward the situation to the thinkpad developer's
list (wherever that may be) and see what they have to say....?

Good luck!
-- 
Jacob Langseth <jlangseth at esisys.com>
CTI Engineer -- Enhanced Systems, Inc.