VPN Bonding/Balancing

[Over Carl]

Got this question for work - at the moment it's pretty irrelevant as we only have a 2Mb sdsl for site to site connectivity although we have been given approval to upgrade to 100Mb.

Now if we have 100Mb both ways at head office for site to site, I was thinking if we can bond or load balance vpn's, then as most of our sites have adsl2+ lines, that could be a potential 48Mb vpn download from head office and if we were to use annex m modulation, that download would go down a bit but upload could go up to 6Mb (2x3mb) up.

However "those that know more than me" have told me vpn bonding is impossible. I dispute this. I have been playing with pfsense boxes as I like these, but can't find a definite answer - I've seen some people suggest you can just set two vpn's and load balance but I can't get a definite answer.

Also I've come across something simliar called zeroshell which definitely supports vpn bonding, although I've seen some forums posts with people saying they don't consider it stable enough for production envoironments.

Before anyone comes up with the usual, riverbed, cisco, juniper, etc are all out of our price range. We're looking at maximum about £4-500 per device for sites and a grand or so for the one at head office.

I suppose I definitely should mention that exponential e is currently my preferred supplier and I would hope to use their vpls service to connect our sites.