Hi Steven,
On 18/08/2015 02:19, Steven Barth wrote:
> Hi Fred,
>
> a few comments:
>
>
> "A host receives on-link prefixes in a Router Advertisement [...] to identify
> preference order among them"
> Is there really a preference order? Also I think off-link prefixes are
> similarly usable for address assignment
> or DHCPv6, they are simply not "on-link".
>
>
> "apart from the fact that it is emitting Router Advertisements (RAs)." -
> wasn't there also a router flag in ND at some point? anyway.
>
>
> "One might expect that the routers may or may
> not receive each other's RAs and form an address in the other
> router's prefix."
>
> Funny enough in theory 4862 says "The autoconfiguration process specified in
> this document applies only
> to hosts and not routers."
>
>
> "Since the host derives fundamental default routing information from
> the RA, this implies that, on any network with multiple prefixes,
> each prefix SHOULD be advertised by one of the attached routers, even
> if addresses are being assigned using DHCPv6."
>
> Hmm, I don't really see the connection between prefixes and (default)
> routing information here, since for non source-dest-capable hosts
> the prefixes do not matter for routing. Or os this sort of a foreshadowing
> of 6724 Rule 5.5?
Not really. Rule 5.5 affects source address selection. We are assuming
that source selection has already happened, and the next job is choosing
the first-hop router. We need both.
>
>
> "A host SHOULD select a "default gateway" for each prefix it uses to
> obtain one of its own addresses. That router SHOULD be one of the
> routers advertising the prefix in its RA. As a result of doing so,
> when a host emits a datagram using a source address in one of those
> prefixes and has no history directing it otherwise, it SHOULD send it
> to the indicated "default gateway"."
>
> The question is to which one (if there are multiple): this might be important
> for e.g. fail-over cases or if you want to dynamically optimize away that
> extra
> hop you mention.
>
>
> "The direct implication of Section 2 is that routing protocols used in
> multihomed networks SHOULD be capable of source-prefix based egress
> routing, and that multihomed networks SHOULD deploy them."
>
> This confuses me a bit since Section 2 said "Because there is no routing
> protocol among those routers" and now suddenly there seems to be one?
There are two scenarios: disjoint routing and a single routing cloud.
I think the diagrams now make that fairly clear, and moving section 4 to
be section 2.2 (as Juliusz suggested) will make the logic easier
to follow.
Brian
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