Some comments on draft-02: - The un-numbered model doesn't require a loopback interface <hs>It does. You may be behind checking your emails on this thread. Pleaseread ample evidence given for this one. </hs>
When Shin was pointing out the considerations for a loopback, Francois- Xavier noted: "When the CPE router has only a link-local address on the WAN port, if the CPE has a LAN bridge, I hope there is an option to have the global- scope address set on the LAN bridge (from IA_PD via DHCPv6) as an alternative to loopback solution." Between Shin, Francois-Xavier, Ole and others it seemed there was an appreciation that loopbacks were not required to support the unnumbered model - best summarised in Shin's email on 3 July. (I'm not suggesting everyone thought the unnumbered model was preferred, but that there was no technical obstacle).
RFC 3484 says:It is RECOMMENDED that the candidate source addresses be the set of unicast addresses assigned to the interface that will be used to send to the destination. (The "outgoing" interface.) On routers, the candidate set MAY include unicast addresses assigned to any interface that forwards packets, subject to the restrictions described below. This seems to hit the nail on the head - we are describing a router that MAY use a unicast address assigned to any interface (LAN) subject to the restrictions in RFC 3484 (which do not pose any problem in my interpretation). I initially raised the use of a loopback as an option because I was concerned about LAN interface state (and said so in the original thread). If the LAN interface is a bridge (always up) I see no mandatory need for a loopback. I would urge continued discussion in- list if there are technical arguments against a un-numbered model without loopback. The two points raised in favour of such an option are that : it avoids an additional /64 for the loopback, and; caters to CPE that may not support a loopback interface (may need to be qualified).
IE (a reference for a routing CPE with internal MAC bridge):
+------------------------+
| Routing CPE w/ bridge |
| +------+ +------+ |
Port1-|-| | | | |
| |Bridge|-----|Router|--|----WAN
Port2-|-| | LAN| | |
| +------+ +------+ |
+------------------------+
LAN is connected to a bridge device so it is always up.
Addresses:
WAN: fe80::<iid>%wan prefixlen 64
LAN: 2001:db8:0:1::<iid> prefixlen 64 (example)
fe80::<iid>%lan prefixlen 64