neilstarling wrote:but it does not change the fact both virtual machines are listening on port 80
That is no problem and has nothing to do with port forwarding...
neilstarling wrote:and the router is not telling owncloud 192.168.1.88 to listen on port 81.
Which would be a) complete nonsens and b) ab-so-lute-ly not necessary.
neilstarling wrote:Am I right in thinking that on other routers you can configure the router to redirect as below:
outside request to router:81 = 192.168.1.88:81 = 192.168.1.88
Yes. On each and every router I have ever seen you can freely choose which external port you want forwarded to which port on an internal IP. The guide to which I linked in my last post explained it more or less...
Perhaps your router is crippled to not let you do this?
Try this, create the following two rules:

- Forward external port 80 to internal port 80
- 80-80.jpg (53.98 KiB) Viewed 347 times

- Forward external port 81 to internal port 80
- 81-80.jpg (53.22 KiB) Viewed 347 times
You then assign one rule to VM1 and the other one to VM2 - that's all and you should be set.
If this does not work, please ask a random network admin.
It should be a matter of minutes to set this up, at least if it is possible with your router.