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I am in a shared working space, sharing with around 100 other companies. Lots of the companies need a VPN between them and developers working externally. The office has a very limited number of external IPs, and the ISP's cost for adding to them is prohibitive.

So is it possible to use some kind of hardware / software configuration to have all VPN traffic come through on custom ports? Our (external) tech support provider says it's not possible, because there are only a limited number of ports that the VPN can work through.

I found this question - Multiple VPN Connections, One IP? - but I don't really understand VPNs well enough to discuss the solution with the ISP or tech support.

What type of VPN do we need to set up? What kind of hardware (if any) could support our requirements?

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VPN is very wide term, what kind of VPN? IPSec, or a SSL-based VPN like OpenVPN? – Jiri Xichtkniha May 11 '12 at 10:47
@JiriXichtkniha Intentionally vague, as different companies have different requirements. However, if the answer was "you can only do this with OpenVPN" then we could at least say that. At present, the answer is "You can't do this". – Blowski May 11 '12 at 10:49
IPSec GW can have many VPNs on one IP. Problem is your silly question, sorry. – Jiri Xichtkniha May 11 '12 at 10:52
@JiriXichtkniha Apologies if the question seems silly to you - as somebody who doesn't really understand IPSec GW, it's not so silly to me. – Blowski May 11 '12 at 11:02
Seems to me that the question is how to provide a bunch of different developers VPN access to a bunch of different servers - and the servers are all behind a single IP address. You need to specify exactly what sort of access the developers need as it may just be a case of providing SSH or FTP access to some servers rather than a VPN joining the developers network to your network. If that is too complex, maybe you should focus on your own problem, and let the 100 other companies worry about theirs. – dunxd May 11 '12 at 11:21

The vast majority of (soft|hard)ware firewalls can manage multiples IPSec VPN with a single external IP. Alternatively you may just have to NAT certains services to give remote users the requested functionnalities.

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You can have multiple IPSec tunnels using a single IP address.

I tend to use Vyatta's, as a virtual router, which I create in my XenServer pools.

Vyatta's are quite easy to configure and there is a lot of documentation to go with it.

Here is a guide to creating multiple IPSec tunnels:

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