Tony Finch – blog

My previous post was incredibly boring and probably quite baffling without any context.

I have recently been preparing my mail servers for IPv6 day. My office mates have been doing similar prep work on their services. Cambridge University's network and DNS have supported IPv6 for a number of years now, and many of the desktops on the computing service staff network use it. Outside the CS the Institute of Astronomy has deployed it extensively, as have the student union and the student-run computing facility, and there is a smattering of it in the Computer Lab and Churchill College. Not much out of a few hundred institutions.

IPv6 day has provided a good push to get us to move our deployment further along. There is not actually much pressure to deploy it here: we have over two hundred thousand public IP addresses (though nearly half of them are dedicated to the Engineering department and the Computer Lab for more-or-less valid historical reasons) and we make extensive use of 172.16.0.0/12 private IP addresses. That should probably be enough for 55,000 people. So progress has been slow.

Our network manager has been looking more closely at rolling out IPv6 to more institutions in the University, and this required coming up with a more detailed addressing plan. It soon became clear that our current 2001:630:200::/48 allocation is uncomfortably small. We have too many institutions to sub-allocate on the /56 boundary, and many of them are too large to fit into a /60 range (only 16 subnets). The colleges have a lot student rooms, and for ease of management it may (eventually) make sense to give them individual /64 subnets, which will easily eat up 2^14 subnets. The federal nature of the University leads to a fair amount of fragmentation, especially since we prefer to allocate on multiple-of-four boundaries to make delegating reverse DNS easier.

After a lot of arguing with JANET and RIPE over their various bureaucratic allocation policies, we have (at last) got the OK for a new /44 allocation. [Since the IPv6 address space is practically infinite, it is obviously important to make sure that we use it efficiently or something. Just like A&A who allocate a /48 to each home user. Obviously there is enough IPv6 space for a one-size-fits-all allocation policy.] As you can see from the list in my previous post, JANET have been allocating /48 ranges to their subscriber institutions, mostly without space between them. This means we can't grow our current allocation because we share our parent /44 with eight other institutions. So we have the joy of a renumbering ahead of us. Good thing it will be small... You can also see from the list that we will be the second UK university to get a /44 after Oxford.