Ubuntu Fan Debuts for Container Networking

Mark Shuttleworth, founder of Ubuntu Linux, explains what the "Fan" is all about.

By Sean Michael Kerner | Posted Jun 23, 2015
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Networking in the Docker container world historically has not been all that easy, but it's now getting easier with multiple new efforts, including one from Ubuntu Linux.

The new container networking technology from Ubuntu is called the "Fan," and it's an interesting model that uses concepts many networking professionals will already be familiar with, in a novel way.

Mark Shuttleworth, founder of Ubuntu Linux, explained to Enterprise Networking Planet that Fan uses NAT (Network Address Translation) for certain use cases.

"If a container on the Fan network wants to talk to non-Fan IP addresses, it is NAT'd on its host. Container-to-container communications are not NATed," Shuttleworth explained. "Essentially, the Fan puts a whole subnet of addresses on a private bridge on each host, and it tunnels traffic between all the hosts. It just does it in a much more elegant fashion than existing overlay networks such as Flannel."

Shuttleworth said that an easy way to understand Fan is to think of it as making each VM in the cloud like your home network, with a NAT gateway and a full subnet behind it.

DHCP (Dynamic Host Control Protocol), which is widely used on networks for IP address assignment, is also part of the Fan model.

"You say, I want to put a Fan behind IP address X, and it makes a little subnet with a DHCP server," Shuttleworth explained. "The addresses on the Fan subnet are mathematically related to address X, so if anyone wants to talk to one of those addresses, they know to route the traffic to address X."

Currently, Fan is IPv4 based and does not use IPv6. The reason why Fan isn't IPv6 based is due to the fact that none of the major clouds support IPv6. Shuttleworth commented that whether the lack of IPv6 support is because they like to charge for IP addresses, or because of limitations in their underlying implementations, is hard to tell.

"This is what creates the scarcity in the first place. AWS will only let you have a very few IP addresses per VM, more for a bigger VM, but not many more," Shuttleworth said. "So the Fan is a stepping stone to full IPv6. It gives us an address expansion mechanism that's IPv4 based, until the clouds provide native IPv6."

Sean Michael Kerner is a senior editor at Enterprise Networking Planet and InternetNews.com. Follow him on Twitter @TechJournalist.

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