[HECnet] Multinet Tunnel Connections to SG1::

[Johnny Billquist]

On 2012-06-07 08:39, Dave McGuire wrote:
On 06/07/2012 02:26 AM, Mark Benson wrote:
Now, you have due permission to beat me with a dried haddock if I'm
being naive (I'm not a programmer, just a user observing a
conversation that's 50% over my head) but...

Wouldn't a kernel-agnostic DECnet implementation be a better shot? I
mean if you can skim DECnet packets using libpcap (which is kernel
agnostic as far as I can tell, hell it even works on Windows :)) and
use that to handle DECnet for the bridge or SimH what's stopping it
being used for a full DECnet comms package? It might not be very
*fast* and it's sure as hell not secure but it'd work, right?

With the fast pace of kernel change and the dropping of kernel
support (and OSs like Ubuntu update the kernel regularly which will
break things) for DECnet in the 3.x kernel it may be that
kernel-based support is no longer practicable on modern Linux.

Just a thought...

    It's a good idea, but I'm not sure it can be done.   We need to change
the MAC address on the interface...can that be done outside the kernel?

No need. See below.

  SIMH uses libpcap and implements networking for emulated machines by
kicking the interface into promiscuous mode.   That's a bit dangerous
from a traffic perspective; I'm not certain that'd be a good idea for
anything other than the most casual use on a quiet network.

Dangerous in which way?
It will create a larger load on the system, but that's about it. And todays machines are fast enough that you really need a lot of traffic before it will become a serious problem from that point of view.
Remember that most of the filtering out of unwanted packets are done in the kernel anyway, and not in user space. That's what the bpf interface and filter programs do for you.

The main reason in the past for changing the MAC address has been that you want to control the source MAC address. However, most systems now allows you to spoof the source MAC when outputting packets on the ethernet, so that problem is solved.

Load is the one remaining reason to even worry, and that is a rather small worry for most people.

With todays network gear, you will not get most packets to your machine anyway, the switches are already doing the filtering for you, so promiscuous mode don't hurt much from that point either.

	Johnny