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

Peter Moreton petermoreton at hotmail.co.uk
Wed Jun 11 04:30:36 EDT 2008

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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