[Simh] FW: FW: FTP client connecting to SIMH/OpenVMS?

[Edward Berry]

NIC cards are very cheap these days, even for laptops. If your laptop has
on-board NIC, you can buy a cardbus 2nd NIC adaptor. Let Windows use one and
the vax use the other. While commuting you can connect them with a 6"
crossover cable. (If the guy in the next seat asks what that's for, you can
say it's a jury-rigged carrying handle; or explain that your computer is
schizophrenic and the cable is so the left brain can talk to the right.)
When you get home you remove the crossover cable and connect both to your
cable router.

Peter Moreton wrote:
>     Thanks for that insight Brad (and others). FYI, the issue affects XP
>     as well as Linux. Now I am aware of the issue, I can work by using a
>     PC on the LAN as a client and a PC on the LAN running SIMH, instead
>     of both Client and SIMH on the same machine. Of course this means I
>     cannot now develop client-server apps on one laptop while commuting
>     on train, but hey.... 
> 
> 
>      
>     ------------------------------------------------------------------------
> 
>      > From: brad at heeltoe.com
>      > To: jeremy at vsm.com.au
>      > CC: petermoreton at hotmail.co.uk; simh at trailing-edge.com
>      > Subject: Re: [Simh] FW: FTP client connecting to SIMH/OpenVMS?
>      > Date: Tue, 10 Jun 2008 20:01:00 -0400
>      >
>      >
>      > Jeremy Begg wrote:
>      > >Peter,
>      > >
>      > >>I just found that I *can* FTP and Telnet into the VMS machine from
>      > >>another Physical host on the LAN - so it seems as though TCP/IP
>     traffic
>      > >>between VMS and the PC running SIMH isn't routing, but so long as I
>      > >>connect to the VMS machine from another PC on the LAN, then the VAX
>      > >>responds as it should.
>      > >
>      > >I believe this is a known problem with SIMH (actually I believe
>     it's a
>      > >problem in the underlying networking library used by SIMH). To
>      > >communicate between the host PC and the emulated VAX, the host PC
>      > >needs to have an ethernet NIC which is dedicated to the VAX.
>      >
>      > if simh is running on linux, it's a long standing issue with
>     linux (and
>      > possibly every other unix)
>      >
>      > Depending on what sort of network "tap" you use to simulate the
>     ethernet
>      > you may not be able to access the simulated host from the host
>     machine.
>      > You can, however, access it from any other host on the network.
>      >
>      > I figured out exactly what the issue was years ago and asked the
>     linux
>      > networking community about it - the response was that most people
>     didn't
>      > notice or care and fixing it was hard.
>      >
>      > It happens more and more now that people are doing emulators as
>     machines
>      > get faster. I've run into before. I think I got around it last by
>      > using an IP level tap internet (i.e. creating a new interface)
>     but that
>      > has it's own set of issues.
>      >
>      > I as I recall (dimly), if you use an ethernet level tap, the ethernet
>      > driver has to duplicate each packet sent and pass them back up to the
>      > simulator socket. Likewise, all packets received have to be
>     duplicated
>      > and sent to the simulator socket. I think right now the receive side
>      > happens but not the transmit side.
>      >
>      > Typing it here is seems simple to fix but it didn't look easy at the
>      > time. Ah yes. the problem is you also want to send packets back
>     to the
>      > host if they originated in the sim. but you don't know who sent
>     them in
>      > the ethernet driver (very low level). so you risk sending packets
>     back
>      > to the host which originated in the host and packets back to the sim
>      > which originated in the sim.
>      >
>      > basically, you want to simulate a mini ethernet wire. I guess you
>      > could do some sort of simple learning bridge.
>      >
>      > Hopefully this illustrates the problem and some of the complexity.
>      >
>      > anyway, simh suffers this problem as do many emulators.
>      >
>      > -brad
>      >
> 
> 
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