Tunnel IPv6 Space

[clay584]

I was wondering why the IPv6 space for the tunnel is a /64?  I know there is a lot of space with IPv6 but why wouldn't you use a /126 or a /127 and then have the larger block for the routed space?

Great program you guys have for IPv6, btw.  I really love it.

[cholzhauer]

Using anything other than a /64 can break other services like SEND and privacy addressing.

[kasperd]

Using anything other than a /64 can break other services like SEND and privacy addressing.

But neither of those is supposed to be used on the tunnel itself, so I don't know what exactly it is that breaks. But until we have gotten rid of the IPv4 backbone it is more productive to keep things as simple as possible on the IPv6 side of things. It is better to spend time upgrading from IPv4 to IPv6 than it is to try and squeeze as much as possible into IPv6 addressing space. So if anything can break depending on the prefix length, then use the one that is least likely to cause breakage.

My guess is that HE is using up more address space on the routed /48s than on all the /64s for tunnel prefixes and routed prefixes. And I guess is that by the time the percentage of 2000::/3 which is in use reaches the percentage of IPv4 addresses in use, the actual percentage in use at that time will be less than 10%.