[Simh] OpenVMS 7.2 VAX telnet failure

[Mark Pizzolato - Info Comm]

As Rick suggested, you should capture traffic in both directions.  Wireshark is an excellent tool for that.  Additionally, Wireshark has built-in protocol decoders which can interpret what is happening in the TCP telnet session.  If you aren’t familiar with, or don’t want to dig into the details of the packet innards, you can save the capture contents, make it available, and let me or someone else can interpret the details and offer analysis.

From: simh-bounces at trailing-edge.com [mailto:simh-bounces at trailing-edge.com] On Behalf Of Lorenzo
Sent: Wednesday, April 30, 2014 7:25 AM
To: Rick Murphy
Cc: simh at trailing-edge.com
Subject: Re: [Simh] OpenVMS 7.2 VAX telnet failure

What nmap is reporting should be the traffic from the VAX to the client.
No matter the client I use (e.g. telnet.exe, PuTTY...), all I get is an endless stream of chars, which matches what appears in the traffic dump.
Upgrading to SIMH 4.0 beta had no effect - after 14 hours I experienced the same exact problem.
During the telnet outage, which happened after ~14 hours of SIMH running, FTP was still working fine.

2014-04-30 2:50 GMT+02:00 Rick Murphy <rick at rickmurphy.net<mailto:rick at rickmurphy.net>>:
At 06:21 PM 4/29/2014, Lorenzo wrote:
Hi!
I'm running OpenVMS 7.2 VAX on a simh emulator, latest release
(V3.9-0 from <http://simh.trailing-edge.com>simh.trailing-edge.com<http://simh.trailing-edge.com>) and compiled with networking (libpcap, no vde).

The emulator has got its own network card to which it's attached.
The host operating system is Linux, kernel 3.11.
My issue is that after an apparently random amount of time (usually a few hours) the telnet server stops working.
I can't get any client to log in remotely - as soon as I connect to the OpenVMS machine,
all I get is a blank character sequence, as follows (dumped by nmap):

SF:NULL,1138,"\xff\xfb\x01\xff\xfb\x03\xff\xff\xff\xff\0\0\0\0\0\0\0\0\0\0


There's a beginning of some TELNET options negotiation going on there.

That's the following:
255 (IAC)
251 (WILL)
1   (ECHO)
255 (IAC)
251 (WILL)
3   (SGA) [Suppress go-ahead)

That's pretty standard.
The series of 0xff (IACs) and nulls that follow aren't.

You really need to capture the traffic to-and-from. Is this coming from the VAX to your client, or vice versa?
        -Rick

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