DATAPUISTOKEMISTI

This post is closely related to my  previous  one. Big difference is that in this case company we bought had Lotus Notes based email system that had to be kept running concurrently with new common email platform for several months. Well, actually it is still running to some extent over 4 years later but that's another story.

Few hours ago you got called to meeting with your boss. You were told that company you're working for just bought another firm and everything needs to be integrated ASAP starting with unifying email addresses.

Some time ago I wrote about how to make multiple unreliable Internet connections function like single reliable Internet connection. That was done using OpenVPN and some iptables trickery. This time we're going to do same without OpenVPN and without iptables.

Here's another interesting little known feature of Linux kernel GRE support.

Often it's not necessary to encrypt traffic when tunneling L2 network over L3 in corporate environment. I hear, you say use OpenVPN, tinc, gvpe, n2n etc. Now, did you know that there's easy built-in solution that has been part of Linux kernel since 2.6.29? If you need encryption just use IPsec to protect GRE traffic.

These are kind of "last resort" fixes if all normal ways fail to resolve problem. No guarantees. Worked for me...