One day at my last job my office doorway darkened. One of our provisioning engineers stood there looking at me with a slightly bemused expression.“I’m configuring the IPv6 addresses on the new backbone links. The wiki says to use a /64. Is that right?”“Certainly. That’s what the addressing plan mandates.”A pregnant silence followed.“That’s a lot of addresses.”“It sure is. 1.845×10^19 to be inexact.”“Especially for a point-to-point link.”“Yup. Couldn’t agree more”A fine sheen of sweat had appeared on his brow.“Ok then.”I’m paraphrasing the conversation but if it seems I sounded terse, well, I probably was. I’d already had this exchange (or a variation of it) multiple times (and often with the same engineers).We’d discussed the pros and cons of the various proposed IPv6 point-to-point addressing schemes. We’d covered the gist of the arguments between the original pro-/64 camp (RFC3627) and the contrarians in the pro-/127 camp (RFC6164; draft-ietf-6man-prefixlen-p2p). We’d talked about the pernicious innumeracy that afflicts the mind when dealing with an number space as large as the one available for IPv6 (as well as the habit of thrift we’d all acquired configuring and managing public addresses with VLSM through an era of relative scarcity).But notably it was never the arguably more subtle issues of neighbor cache exhaustion, ping-pong attack, or router-subnet anycast conflicts that persisted in the minds of my fellow engineers. Rather, what ultimately consumed their imaginations (and caused the perspiration) was “that’s a lot of addresses.”This anxiety is encapsulated nicely in the pro-/127 IETF draft. In one of its more philosophical moments the draft asserts “though address space conservation considerations are less important for IPv6 than they are in IPv4, it may still be desirable to use the smallest possible prefix to number links.”The truth of the assertion is not likely to be ultimately tested during any of our respective professional (or even biological) lives.What are readers choosing to use for the point-to-point links in their networks?
