Re: [v6ops] M/O flags and PD

[Gert Doering <[e-mail]>]

Hi,

On Fri, Oct 30, 2015 at 09:10:55AM +0100, Tore Anderson wrote:
> * Gert Doering <[e-mail]>
> 
> > I do not have RFCs to counter that, but my interpretation is a bit
> > different.  I see that section of 4861 as traditionally applied to 
> > *hosts*, while IA_PD traditionally is a *router* function, so out of 
> > scope for the "host part" of 4861.
> 
> Section 4.2 of RFC 4861 simply describes the RA message format, it's
> not in a "host part" of the RFC as far as I can tell. Keep in mind that
> RAs are typically multicast to all IPv6 nodes, so the originating router
> does not know whether it is a host or a router (or both, or none) that
> will be receiving the RA.

Yes, but that is the point - "typical routers" do not need to *listen* to 
RAs, because that's not required for their job.  They will speak a 
routing protocol, and not default-route, etc.

As I said, boundaries between "hosts" and "router" are less than clear
today - but this is my interpretation on how these have come into place.

> Thus, when determining whether or not to set the M/O flags, the
> [operator configuring the] RA originating router will have to ask
> himself the following question:
> 
> «Is there information available through DHCPv6 to nodes on this link?»
> 
> If the answer to that question is «yes», the M or O flag should be set.
> If the answer is «no», they should be both unset.

There might not even *be* a RA if this is a pure router-to-router link...

> > Now this gets all muddled together when you have a router that also 
> > wants an address for itself (= acting as a host for that purpose) or 
> > a host that wants a prefix (= serving as a router for that prefix).
> 
> I'll note that this discussion started with a comment on
> draft-jjmb-v6ops-unique-ipv6-prefix-per-host. This draft talks about
> hosts, not routers. It even says so right there in the file name and
> the title.

True, but as soon as a host requests a prefix for "a bunch of VMs" running
on that same host, and forwards traffic between "the outside router" and
"the various VMs", it very much becomes a router...

Gert Doering
        -- NetMaster
-- 
have you enabled IPv6 on something today...?

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