[Simh] VAX XQ and wireless networking

[Gary Lee Phillips]

Well, just to confirm what I thought I remembered:

I tried again to set up bridging, and it is not possible using the
method that works for wired ethernet. That is, I define a bridge br0
using the brctl command (as root of course) and then add interfaces to
the bridge. I can add eth0 without difficulty, just as on other
machines. But if I try to add the wireless interface wlan0, the
command is rejected:

can't add wlan0 to bridge br0: Operation not supported

I have used iptables (and earlier versions of the command, ipchains or
ifwadm) to set up software firewalls before, and even to NAT ip
addresses, but I've never seen a way to make it change a MAC address.
Even if I had, I have no idea how to apply that to the output of the
SIMH XQ device. Are you saying I should create a tun device or
something similar to which XQ0 can be attached, and then re-route
packets from that device to wlan0 by using iptables?

I believe if IP were working, then DECNET can be routed or
encapsulated over IP. But in this particular case, DECNET is
inessential if I have working IP. The working IP tools and clients are
sufficient. And I thought DECNET Plus didn't need to mess with MAC
addresses anyway. Isn't it just DECNET IV that does that?

On 11/17/12, TJ Merritt <simh at tj.merritts.org> wrote:
> The TUN interface will get the packets injected into the system, but
> will not get them bridged across the wireless network which uses the MAC
> address for managing the wireless network.  Since your MAC address for
> the virtual interface is not the same as the mac address for the host,
> reply packets over wireless will get dropped.  The trick is to get the
> packets to go out with the host's MAC address and replies routed back to
> the virtual interface.
>
> VirtualBox does this by sending packets out with the original IP address
> but the MAC address of the host, they then record the virtual interface
> that the IP address came from, when the reply packet comes back, they
> use the IP address to look up the virtual interface associated with that
> IP address and route the packet to that interface.  There are special
> cases of course for things like broadcast, multicast, and IP addresses
> that are shared between multiple VM's.  VirtualBox does not currently
> support IPv6 addresses though. This would also not help for DECnet.
> This is effectively a layer 3 switching capability that works around the
> lack of layer 2 switching in the wireless network.
>
> Another approach would be to setup NAT so that the NAT layer can take
> care of the MAC address rewriting.  It will also rewrite the IP address
> though.  If this is satisfactory, you there should be plenty of NAT
> resources available to you on Mint such that no code writing is
> required.
>
> Adding virutal networking support for wireless networks would be a major
> undertaking for SimH, but if done, could eliminate most of the hiccups
> with virtual networking over wireless networks.
>
> Of course, not of these issues occur over wired netowrks.
>
> -- TJ
>
> On Sat, 2012-11-17 at 15:24 -0500, Dan Gahlinger wrote:
>> It works...
>> use the TUN interface and the bridging, works just fine.
>>
>>
>> Dan.
>>
>>
>> > Date: Sat, 17 Nov 2012 14:14:24 -0600
>> > From: tivo.overo at gmail.com
>> > To: simh at trailing-edge.com
>> > Subject: [Simh] VAX XQ and wireless networking
>> >
>> > Is this even possible? I have SIMH 3.9 on Linux Mint 12, running the
>> > VAX with OpenVMS 7.3. It works great, except for networking. The
>> > hardware is ASUS EeePC with Atheros AR5001 wireless network adapter
>> > and Atheros L2 Fast Ethernet adapter.
>> >
>> > I have libpcap version 1.1.1 (which is also callable as version 0.8)
>> > installed on Linux. The VAX module was compiled with networking
>> > enabled.
>> >
>> > The configuration file has an "attach xq0 wlan0" or "attach xq0
>> eth0"
>> > depending on which interface I'm trying to use. With the wired
>> > ethernet (eth0) I am able to use both TCP/IP and DECNET Plus. With
>> the
>> > wireless (wlan0) neither one works.
>> >
>> > I've tried disabling the DECNET IV compatibility mode, which was
>> > recommended in one source for wireless compatibility, and also tried
>> > adding "set xq xx-yy-zz-aa-bb-cc" (with the actual MAC address of
>> the
>> > wireless adapter) to the configuration. The first did nothing I
>> could
>> > discern, and the second generated an error message during startup of
>> > the SIMH module, saying that the MAC address was already in use and
>> > could not be assigned.
>> >
>> > Obviously the workaround is to use a cabled connection when the VAX
>> > emulator is needed, but this isn't very practical in most cases. Is
>> > there any other possibility I've overlooked?
>> >
>> > I notice that this is a frequently found question when using Google
>> to
>> > look for answers, but I found no responses other than the two
>> > solutions mentioned above. I suppose a different network card
>> > emulation for VAX could make the wi-fi adapter look like a normal
>> > ethernet interface, but apparently that hasn't been done yet and
>> it's
>> > probably beyond my very rudimentary C coding abilities.
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>>
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