On Thu, 3 Jan 2008, Mark Smith wrote:
It's also common for CPE to run a caching DNS servers and NTP peers these days, which the downstream devices can use, so they'd break too.
No, the CPE would use a loopback address for sourcing packets destined to the outside (or it's LAN adress).
I understand the motive for the suggestion, however I don't really see how it couldn't be more trouble than it's worth. A ULA prefix on that upstream link would address some of the issues, but not all of them. I think to provide global Internet access you really need to ensure a fully globally addressed path to and from the Internet.
So you think that "ip unnumbered loopback0" in IPv4 is really weird to have on WAN interface? It's basically the same thing.
-- Mikael Abrahamsson email: swmike@swm.pp.se