nanog mailing list archives
Re: ISP customer assignments
From: Bill Stewart <nonobvious () gmail com>
Date: Mon, 19 Oct 2009 19:02:34 -0700
If you've got an addressing system with enough bits that you don't have to start stealing them, it makes sense to pick some boundary length between our-problem : their-problem 128 bits is long enough, and changing protocols is nasty enough, that it should let you Never Have To Do It Again. Originally with IPv6, the boundary was a nice round 64 bits, with the ISP on the network side and MAC48-based autoaddressing on the user side, with the user side looking suspiciously similar to Novell Netware and giving ~64K subnets, and this was back before DHCP had taken over the world and it was expected that all kinds of weird little toasters would be using IPv6. But some relatively sensible people proposed using the (ugly) EUI-64 64-bit MAC, because they Never Wanted To Have To Do This Again Either. And unfortunately, because it's a good enough idea to be worth accepting, it pushes the network boundary somewhat to the left, because it's pretty obvious that an average household may have multiple devices that want to autoconfigure themselves, so you probably will end up needing multiple subnets. And unfortunately, there's no obviously correct boundary, and no particular reason for all ISPs to use the same boundary, so there are endless arguments about it on NANOG and elsewhere. In general, /48's big enough for most large complex businesses (except ISPs), and /60's more than big enough for a household and for many small businesses, but we've got enough bits that it's worth using octet-aligned addresses, so /56 is the magic number for them, except at ISPs that simply don't want to bother giving out anything except /48s. There may be special cases for assigning /64s to end users, such as IPv6-equipped cell phones, but that's a matter for specialized carriers to provide, or for internal network managers at enterprises. And if you're big enough to get Provider Independent Address Space and an AS#, you're big enough to have a /48 of your own. Now, IPv6 was supposed to allow the development of other indistinguishable-from-magically advanced technology, such as getting rid of the growth of routing tables by convincing everybody to be happy with hierarchically assigned provider-aligned address space, and unfortunately that hasn't matched the needs of businesses, which need multihoming for reliability (so they'll be non-provider-aligned for at least n-1 of their ISPs), plus want the ability to take their address space with them when they change ISPs (because there are too many devices and applications that insist on having hard-coded IP addresses instead of using DNS, and because DNS tends to get cached more often than you'd sometimes like. So that problem shows no sign of going away (in spite of shim6..)
Current thread:
- Re: ISP customer assignments, (continued)
- Re: ISP customer assignments Chris Adams (Oct 15)
- Re: ISP customer assignments Nathan Ward (Oct 15)
- Re: ISP customer assignments Dave Temkin (Oct 15)
- Re: ISP customer assignments Rob Evans (Oct 16)
- Re: ISP customer assignments William Herrin (Oct 15)
- Re: ISP customer assignments Tore Anderson (Oct 16)
- RE: ISP customer assignments Wouter de Jong (Oct 14)
- Re: ISP customer assignments Joel Jaeggli (Oct 13)
- Re: ISP customer assignments Justin Shore (Oct 13)
- Re: ISP customer assignments Michael Dillon (Oct 13)
- Re: ISP customer assignments Bill Stewart (Oct 19)
- Re: ISP customer assignments Nathan Ward (Oct 19)
- Re: ISP customer assignments bmanning (Oct 19)
- Re: ISP customer assignments Nathan Ward (Oct 19)
- Re: ISP customer assignments Bill Stewart (Oct 20)
- Re: ISP customer assignments Mark Andrews (Oct 20)
- Re: ISP customer assignments Karl Auer (Oct 20)
- Re: ISP customer assignments Mark Andrews (Oct 20)
- Re: ISP customer assignments Roland Dobbins (Oct 20)
- Re: ISP customer assignments Mark Andrews (Oct 20)
- Re: ISP customer assignments Roland Dobbins (Oct 20)