One of the long-standing debates that cloud proponents are having to deal with concerns the portability of cloud providers.

>VMware is happy to talk about cloud portability - the company points out that users can easily move from their own data centre to a cloud provider, back to their own data centre and to a different provider without any major redevelopment work needed - and so they can, as long as they're using VMware's vCloud Director.

But there's another approach. A new(ish) company Cloudswitch has a completely different approach - one that's hypervisor-neutral and one that seems to offer the degree of portability that many companies crave.

It uses a technology that seems somewhat old-fashioned now - a network bridge. Veterans of the industry will remember bridges used to be used in networks, operating at Layer 2 of the OSI stack  but were largely superseded by routers, operating at Layer 3, which offered more scalability and worked by directing to IP addresses rather than MAC addresses.

But Cloudswitch has developed a new variant on bridging technology and created an encrypted bridge that links data centres to cloud computing providers. Crucially, CloudSwitch uses a combination of Layer 2 and Layer 3 technologies to offer a hybrid solution to connecting to the cloud.

Adopting this approach means that CloudSwitch has avoided two of the problems faced by pure-play Layer 3 technology: the fact that it's location-dependent and that it's problematic to configure virtual machines in line with changes in the cloud,

Layer 2 bridging gets around this but throws up other issues - particularly as regards security

So, CloudSwitch has developed a hybrid solution for cloud computing. Hybrid is a word bandied around a lot when it comes to cloud, normally meaning a mixture between public and private. In this case, however, it's the combination of Layer 2 and Layer 3 technology that provides the heady mix.

John Considine, Cloudswitch's CTO has a long history, being part of the engineering team for many of Sun's NAS products, having fetched up at the company thanks to Sun's acquisition of Pirus. It's this background that perhaps has given him the philosophy behind CloudSwitch.

"You need to make cloud seem like a node on the customer network, everything about the app seems like it’s running in the data centre," he says.. "Our software can be installed in 20 minutes and users can be guaranteed that everything is encrypted. What's more, they can keep everything from their data centres - IP address, MAC address - there's no additional configuring to do"

As Considine points out, moving from one cloud provider's data centre to another can be a bit of a pain. "Imagine I’m running an app inside my data centre in the US. If I move that app to an Amazon cloud in the UK, it’s now got a different set of attributes - it’s on a different subnet.I either have to change routing tables or DNS server, so there's some work to do. With software, there's no configuring."

Best of all, the software is hypervisor-independent: it works with Amazon (which is based around Xen) and Terremark (a VMware-using provider) but the company is looking to support other cloud providers - it's currently talking to three more but won't reveal their names.

CloudSwitch is available to download for trial (there's also a free version for five VMs). It does look like a neat solution to a problem that many data centre managers are going to face and is well worth playing with.

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