[HECnet] Connections?

[Johnny Billquist]

What Mark actually is talking about, and referring to, is the question 
if sending packets are also seen by others connected to the same 
interface and receiving packets.

It's a bit more complicated than just saying "BSD" does this, or "Linux" 
does that. But the bottom line is that some systems, and some hardware, 
makes outgoing packets also visible to programs reading from the 
interface, and other combinations do not.

And if you do not receive outgoing packets, then two virtual machines on 
the same host, using the same interface, cannot communicate with each other.

   Johnny

On 2018-05-06 04:00, Mark Pizzolato wrote:
> Mark,
> 
> I’ve seen no evidence that anything has changed at all on Linux or other 
> operating systems.   Changes have been made within simh to better 
> support some situations where bridges are used, but some sort of bridge 
> setup needs to be done like it did long ago.
> 
> Please point at specifics of what you are seeing that now allows telnet 
> to an emulator’s IP address without setting up some sort of bridging.
> 
> -Mark
> 
> *From:*owner-hecnet at Update.UU.SE [mailto:owner-hecnet at Update.UU.SE] *On 
> Behalf Of *Mark Abene
> *Sent:* Saturday, May 5, 2018 3:57 PM
> *To:* hecnet at update.uu.se
> *Subject:* Re: [HECnet] Connections?
> 
> Nothing of the sort. I'm saying that in the past, you couldn't telnet to 
> an emulator's IP address from within the same host server. Naturally the 
> host server has multiple IPs for all the emulated guest OSes. This was a 
> well known and well documented peculiarity of BSD and Linux when logged 
> into a shell on the host server. It's no longer the case on more recent 
> Linux systems.
> 
> -Mark
> 
> On Sat, May 5, 2018, 10:56 AM Mark Pizzolato <Mark at infocomm.com 
> <mailto:Mark at infocomm.com>> wrote:
> 
>     Hi Mark,
> 
>     I’m not understanding what you saying here.
> 
>     Are you suggesting that on a single host system, you’ve got multiple
>     independent simulators running which all are using the same IP
>     address as the host system? And, if true these devices can then, not
>     only uniquely communicate with remote systems (on the Internet say),
>     and also to each other AND the host system?
> 
>     -Mark
> 
>     *From:*owner-hecnet at Update.UU.SE <mailto:owner-hecnet at Update.UU.SE>
>     [mailto:owner-hecnet at Update.UU.SE
>     <mailto:owner-hecnet at Update.UU.SE>] *On Behalf Of *Mark Abene
>     *Sent:* Saturday, May 5, 2018 10:45 AM
>     *To:* hecnet at update.uu.se <mailto:hecnet at update.uu.se>
>     *Subject:* Re: [HECnet] Connections?
> 
>     This is an often misunderstood generalization, with some people able
>     and others not. I remember this being true on *BSD. You could not
>     connect to a simulated IP on the same host. It *used* to also be
>     true on Linux, but is no longer the case for some time. On my ubuntu
>     server where I run dynamips, simh, and klh10, all on bridged taps, I
>     can telnet to all instances, even locally.
> 
>     -Mark
> 
>     On Sat, May 5, 2018, 12:27 AM Johnny Billquist <bqt at softjar.se
>     <mailto:bqt at softjar.se>> wrote:
> 
>         On 2018-05-05 03:39, Robert Armstrong wrote:
>          >>since once Multinet grabs the interface, I can’t get to the
>         underlying
>          > host.
>          >
>          >    Actually I think it’s a limitation in simh and the pcap
>         library – the
>          > simh guest OS can’t talk to the host OS on the same
>         interface.  You can
>          > work around the problem with a TAP device.  Check the
>         archives for the
>          > simh mailing list – it’s been discussed many times before.
> 
>         No. That is not correct. I run simh myself on a machine where I
>         have
>         both the native host and simh talking on the same ethernet. And
>         they are
>         both reachable by other hosts.
>         The OP must be doing something else funny.
> 
>             Johnny
> 
>         -- 
>         Johnny Billquist                  || "I'm on a bus
>                                             ||  on a psychedelic trip
>         email: bqt at softjar.se <mailto:bqt at softjar.se>             || 
>         Reading murder books
>         pdp is alive!                     ||  tryin' to stay hip" - B. Idol
> 

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol