daft IP addressing choices

This is only one of the reasons why squatting in other people’s netblocks is a bad idea. To understand the point, you’ve got to go back to the BT 21CN project, which was one of those “the Internet is just another service over our private network” ideas telcos tend to love. Although a lot of it didn’t work, like the weird ethernet-level multiservice router, they did build a huge MPLS core network that carries all the other stuff – i.e. mostly the Internet – as encapsulated traffic.

Because they did it this way, they also didn’t do IPv6, which left them with a problem. One of the advantages of doing it the way they did was that they could trivially have a parallel management network. But that meant finding at least two addresses per device for the whole of the UK. So they had the bright idea of picking a big netblock that doesn’t appear in the Internet routing table, and “borrowing” that.

Sensibly, they looked for one that would be very unlikely to ever be announced. Some organisations who got huge IP allocations back in the day, like MIT with its 3 /8 blocks, have been prevailed on to give at least some of them back for public use. The classic case is the trade show Interop, which used to own 45/8 and only use it one week a year.

The US Department of Defense, however, has a hell of a lot of address space, and usually doesn’t route publicly for fairly obvious reasons. And if they don’t want to give it up, who’s going to make them? So they peeked into the DODNIC allocation and picked 30/8. This is quite common; one day somebody will audit it all and there will be surprises.

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