Network connectivity

Clive B. Dawson (CLIVE@XX.LCS.MIT.EDU)
Fri 4 Nov 88 04:23:32-EST

MCC.COM ( has unable to establish connections with a large
percentage of the Internet hosts during the past 24 hours. I believe
much of this is caused by the fact that a lot of gateways have been
turned off to try and prevent the spread of the Unix virus that's been
going around. Furthermore it looks like there's a lot of "one-way"
gateways out there. OUr SMTP listener has had a lot of connections
hanging in SYN.SYN state and timing out, presumably because our SYN's
aren't making it back to the host who is trying to connect to us.

But I really got confused when I discovered that many of the hosts
I couldn't connect to were reachable from other hosts on the 10 net
(e.g. Score and XX). If anybody can offer one or more explanations for
this, I would very much like to hear about it. In particular,
what are the possible causes for a host being reachable from 10.a.b.c
but not from 10.x.y.z? (Note that MCC.COM's "default,preferred"
address IS The only explanation I can come up with
is that something is messed up in the PSN routing tables, and that
this is a problem for the NOC.



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