Interested in input on tunnels as an IPv6 transition technology

Iljitsch van Beijnum iljitsch at
Fri May 13 08:02:40 UTC 2011

On 13 mei 2011, at 7:52, Karl Auer wrote:

> I'm working on a talk, and would be interested to know what people think
> is good about tunnels as an IPv6 transition technology, and what people
> think is bad about tunnels.

Without tunnels we'd have no IPv6 today. Even today many people, especially home users, depend on them. But it would have been impossible to get IPv6 started by running it native-only.

Tunnels can work very well and if they're direct they can be almost as good as native connectivity. However, in the past we saw Europeans get tunneled IPv6 connectivity from Japan. That kind of thing is very bad because it inflates RTTs and thus slows everything down.

Enabling automatic tunneling by default is also a mistake because then you think you have IPv6 even if the automatic tunnel doesn't work because relays are unreachable or stuff is firewalled.

A downside of tunneling is the reduced MTU, but hopefully the fact that tunnels are common makes people fix PMTUD problems rather than blindly send 1500-byte packets and let the chips fall where they may that way too many people do with IPv4.

So... tunnels can be good or can be bad, but native is still better than a good tunnel.

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