RE: [homenet] ULA scope [draft-ietf-6man-rfc3484-revise-05.txt]

[Anders Brandt <[e-mail]>]

Tim Chown wrote:
>Wednesday, March 21, 2012 12:55
> On 20 Mar 2012, at 21:25, Brian E Carpenter wrote:
> 
> > On 2012-03-20 21:51, Anders Brandt wrote:
> >>
> >> It is a surprise to me that ULA addresses are not by default routable
> within the site.
> >> I can easily imagine a number of LLN border routers which
> >> autonomously allocate different ULA prefixes for use within their
> individual LLN subnets.
> >
> > IMHO that should be a NOT RECOMMENDED behaviour. ULAs make sense if
> > they cover an entire enterprise or home network, but not if they cover a
> subset.
> >
> >> Meeting a ULA address outside the local prefix will cause the LLN
> >> node to forward its IP packets to the default gateway (border router)
> >> of the LLN subnet. This way packets can travel between LLN subnets
> >> using normal routing with long-term stable ULA addresses. We need the
> stable addresses for control-style applications in LLNs.
> >>
> >> Obviously it requires a routing protocol in the (homenet) LAN but are
> there other issues?
> >
> > It doesn't just require a routing protocol; it also requires a routing
> > policy that knows which routers have to block the ULAs (plural). That
> > seems a lot more complex that a rule that says only a border router
> > originates and delegates a ULA prefix, because that border router
> > would also know to block the prefix across the border.
> 
> So we need to determine what the homenet arch text will say on this.
> 
> I think the assumption so far has been that, as per PD8 in draft-ietf-
> homenet-arch-02, one router would be elected the "master" to delegate /64
> ULA prefixes within the homenet, both to ULA-only LLNs and to links that
> also have a GUA prefix.  If there's an assumption an LLN router will not
> support that, and instead generate its own /48 ULA, we need to talk about
> that, or any other scenario that will lead to multiple /48 ULAs in a single
> homenet site.
> 
> The arch text currently says that ULAs should be used (CN1) and that ULAs
> should be preferred for internal communications to GUAs (section 2.4).  It
> doesn't say how connections from outside the homenet can be made to
> internal ULA-only devices.

Is it obvious that you want to do that?
I thought the entire ULA discussion was homenet internal only?

Access from the outside will require tunneling or an additional global
address, I guess?

- Anders

> The 3484-bis text has changed the default ULA preference to protect against
> ULA leakage, so if you now want ULAs preferred you need to somehow
> inject the specific site /48 ULA being used with high precedence into the
> policy table (and as also pointed out here if your site is using less than a /48,
> you should also have some way to learn what the site prefix length is). In
> the homenet case is that injection achieved on receipt of an RA, or would it
> require the proposed DHCPv6 option to be used (which may not be widely
> implemented for some time, and the DHCPv6 server still needs to learn the
> ULA to put in the option)?
> 
> On the one hand homenet is saying "we'd prefer to use ULAs by default
> without needing some magic to achieve it" while 6man is saying "we need
> to protect against ULA leakage, so if you want to prefer ULA for internal
> connection stability figure out the magic".
> 
> This needs to be mapped to words for the homenet arch text.
> 
> Tim
> 
> >
> > Anyway - maybe you should look at draft-liu-v6ops-ula-usage-analysis
> > and discuss it over on v6ops.
> >
> >    Brian
> >
> >>
> >> Thanks,
> >>  Anders
> >>>> You'll find the above logic in the current 3484bis draft.
> >>>>
> >>>> -Dave
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