Re: [v6ops] Flash renumbering

[Philip Homburg <[e-mail]>]

> > If there are multiple downstream subnets and the router announces a ULA, the
> n
> > it becomes more complex because for the ULA, the router is still a default
> > router.
> [Ed: ] Good comment. But sorry it is even more complicated. I
> propose to simplify a little.  1. Following this logic we would
> come to the situation when default router announcement should be
> related to the fact that routing table has some particular route.
> It means: ND would become involved into routing. IMHO: it is too
> much.  

Suppose that a router has 2 downstream subnets, fd00:0:0:1/64 and fd00:0:0:2/64
and one of these subnets has an extra router that connects to the internet
without knowing about these ULA prefixes. This is common in poor man's 
multi-homing

In that case hosts need to have some understanding of routing and RIOs, or
it becomes a very tricky game of default routers and preferences.

> 2. I propose to disable "default router" in RA only If all
> uplinks are disconnected (the router could not play router primary
> role anyway). 

In my example, if the router has no connection to the internet, but it does
connect to another subnet, does that mean that all of it's uplinks are
disconnected?

> On-link ULA (or GUA) communication would not be
> affected (if L flag was set).  You would probably say in response
> that router is not just forwarding traffic to outside - it is
> additionally redirect and switch locally for the case when prefix
> was announced with L bit cleared.  Well, it is possible to fix by
> small ND update:  - it is not prohibited by current ND specification
> to redirects and forward local traffic for the state when router
> announce 0 default router lifetime - probably should work for many
> current implementations.  - but host would probably not send traffic
> to router that is not default (even for traffic inside PIO).  What
> if we add the rule: host could always send traffic to the router
> (irrespective to router lifetime) if traffic is destined to node
> that is inside prefix announced by this router.  It is effectively
> different definition of "local": "router is always local for all
> hosts in the prefix announced by this router". Or in another way:
> "link is never disjoint" ????? Then would be the nice solution for
> router that lost global connectivity. Irrespective: ULA or GUA.

Instead we could have a RIO that covers the prefix...

> > One option would be to change the priority of the router, but that would mak
> e
> > address section more complex in the case of a multi-homed network.
> >
> > One option would be to move away from default routers and only have Route
> > Information Options (RFC 4191).
> [Ed: ] I am hesitant to qualify: was it right or wrong.  But I
> would like to point that this ND extension was not included into
> the current ND specification.  [Ed: ] It means that there were 6man
> consensus in 2007: it is too much to inject routing information
> into ND.

RFC 4191 is standards track. I don't think it needs to be textually included
in ND.