On 2010-09-20 20:45, Leo Vegoda wrote: > On 20 Sep 2010, at 12:39, Adrian Kennard wrote: > > [...] > >>> I understand that the PEN space is infinite. Of course, typing a *very* >>> long string of numbers into a configuration might be a bit awkward. >> >> Now why could they not have done that for IP addresses :-) > > I was told that variable length IP addresses were considered in the early > design stage but we didn't go there because it is cheaper to produce > equipment that processes fixed length addresses. Hopefully 128 bits will be > enough for the next century.
Indeed, quite understandable, it did have a smiley... Though I did wonder whether one could have done it with a fixed initial space, like 24 or 32 bits, that are AS number, and then variable after that, which ISPs might have chosen to be fixed or variable depending on size of ISP and choice of vendor, and so on. Even then, the ISP may work on a fixed size and pass to end user. Making a small DSL router handle variable space with software routing is easy. I.e. not infinitely variable, but variable in a few logical and common steps. Back haul would use a smaller fixed size to target AS in high speed hardware routing. ISPs would use smaller smarter routers. End users would have totally s/w routed kit with more flexibility. Of course that would give every AS infinite IP space and make a large part of RIRs and LIRs job totally pointless. It would have been cool if my IP was 20712.3342760.3.1 I.e. AS 20712, UK company 3342760, Office 3, machine 1 (assuming AS 20712 chose to allocate based on company number for example)
