Re: [6lo] Advocating a generalization of RFC8505 to non-6lo LANs

Mark Smith <markzzzsmith@gmail.com> Thu, 04 July 2019 12:39 UTC

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From: Mark Smith <markzzzsmith@gmail.com>
Date: Thu, 4 Jul 2019 22:38:50 +1000
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To: "Pascal Thubert (pthubert)" <pthubert@cisco.com>
Cc: Carsten Bormann <cabo@tzi.org>, Michael Richardson <mcr+ietf@sandelman.ca>, V6 Ops List <v6ops@ietf.org>, 6man <6man@ietf.org>, "6lo@ietf.org" <6lo@ietf.org>
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Subject: Re: [6lo] Advocating a generalization of RFC8505 to non-6lo LANs
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On Thu., 4 Jul. 2019, 21:38 Pascal Thubert (pthubert), <pthubert@cisco.com>
wrote:

> This is all very right, Carsten.
>
>
> > RFC 6775/8505 on a new (greenfield) foo (as in IP over foo) is pretty
> much a
> > no-brainer, if that foo has points where the 6LBR functionality is
> naturally
> > centralized.
>
> No brainer it is, but for Lorenzo's issues on state preservation or
> reconstruction upon router reboot.
>

I think that can be overcome.

I've been thinking for a while how to build something like this using
existing protocols and host or router behaviour.

Fundamentally two stages:

- collect nodes' link local addresses

- query nodes' for their other GUA or ULA addresses

Collecting nodes LLAs can be done via collecting source addresses from node
emitted RSess and/or MLDv2 reports.

Once they've been collected, then nodes are unicast queried by routers for
their other addresses via either ICMPv6 Node Information queries or Inverse
ND.

(There is currently a limitation with ICMPv6 NI that it doesn't report
temporary addresses for security reasons. That could be lifted by e.g.
saying that all addressed including temporaries are reported if the NI
query source address is an LLA i.e. limited to a query from an on-link
source, or both LLA source and that the LLA is that of a known default
router.)

A new node on the link effectively announces its LLA to existing routers
via RS and MLDv2 joins for solicited node groups for its addresses (and
other multicast groups it may join).

If a node configures a new address, it joins the address's Solicited Node
Multicast group. Routers use that as a signal to unicast query the node it
for its updated address list to discover the new address.

(DAD is another possible way for routers to collect new address
information, however I think Ericsson have some IPR over that idea, and it
also doesn't work for anycast addresses, because DADs aren't performed for
them).

Routers detect when an address disappears via standard ND NUD.

A new router on a link can collect existing nodes' LLAs via a general MLD
query, as it does anyway to collect the set of multicast groups on the
link. Once the new router has that set of LLAs, it then unicast queries the
nodes for their other addresses.


Perhaps a bit of pedantry, however if nodes are "Neighbours", since we now
have possibly multiple addresses per node/neighbour, ND isn't really
discovering neighbours, it's actually discovering the presence of
addresses, not "neighbours". Address Discovery or Address Presence
Discovery would perhaps be a more accurate name for this function.

Regards,
Mark.



> > Not so easy for brownfield, i.e., in networks where classic ND is
> already used in
> > some hosts and some routers.  “Efficient ND” (which was essentially RFC
> 6775
> > for Ethernet and thus also traditional Wi-Fi) mostly didn’t take off at
> the time
> > because we didn’t articulate a cohabitation (“transition”) strategy.
> I’m sure
> > we can do that if we put a little more focus on it, leading to another
> > specification that describes how to run in mixed classic/efficient ND
> networks.
>
> For I started that at 6lo and there is text in
> https://datatracker.ietf.org/doc/html/draft-ietf-6lo-backbone-router ,
> e.g., in section 3.2. The coexistence is also discussed in
> https://tools.ietf.org/html/draft-thubert-6lo-unicast-lookup but at some
> point it is not a 6lo problem anymore and that work should really move
> somewhere else.
>
> Being non-maintenance, it seems too early for 6MAN. If so maybe we should
> form a short-lived WG to sort out the issues raised by Lorenzo,  yours
> (coexistence) and mine (limit use of broadcast / interface with a fabric
> mapping server and do unicast lookup when possible).
>
> All the best,
>
> Pascal
>
> > -----Original Message-----
> > From: Carsten Bormann <cabo@tzi.org>
> > Sent: jeudi 4 juillet 2019 13:22
> > To: Pascal Thubert (pthubert) <pthubert@cisco.com>
> > Cc: Michael Richardson <mcr+ietf@sandelman.ca>ca>; 6lo@ietf.org; V6 Ops
> List
> > <v6ops@ietf.org>rg>; 6man <6man@ietf.org>
> > Subject: Re: [6lo] Advocating a generalisation of RFC8505 to non-6lo LANs
> >
> > RFC 6775/8505 on a new (greenfield) foo (as in IP over foo) is pretty
> much a
> > no-brainer, if that foo has points where the 6LBR functionality is
> naturally
> > centralized.
> >
> > Not so easy for brownfield, i.e., in networks where classic ND is
> already used in
> > some hosts and some routers.  “Efficient ND” (which was essentially RFC
> 6775
> > for Ethernet and thus also traditional WiFi) mostly didn’t take off at
> the time
> > because we didn’t articulate a cohabitation (“transition”) strategy.
> I’m sure
> > we can do that if we put a little more focus on it, leading to another
> > specification that describes how to run in mixed classic/efficient ND
> networks.
> >
> > Grüße, Carsten
> >
> >
> > > On Jul 4, 2019, at 12:28, Pascal Thubert (pthubert) <
> pthubert@cisco.com>
> > wrote:
> > >
> > > Hello Brian:
> > >
> > > Yes, I'm willing to make the case.
> > >
> > > There are a number of reasons to enable a registration method on beyond
> > 6lo networks:
> > > - It is useful in wireless in general because it addresses non-transit
> > > multipoint links (see
> > > https://datatracker.ietf.org/doc/draft-thubert-6man-ipv6-over-wireless
> > > /) and NBMA ML-subnets
> > > - it is useful in particular in Wi-Fi because it reduces the need for
> broadcast
> > quite dramatically.
> > > - It is useful in a switched fabric to maintain an accurate state in
> > > the overlay mapping server (see
> > > https://datatracker.ietf.org/doc/draft-thubert-6lo-unicast-lookup/)
> > > - It is useful in a situation of host mobility in general, (see the
> > > discussion in
> > > https://tools.ietf.org/html/draft-ietf-rift-rift-06#section-5.3.3 )
> > > - It is useful for routers with hardware assist forwarding to avoid
> > > the punting dance and dropping of packets
> > > - It provides SAVI properties with a workable Secure ND (see
> > > https://datatracker.ietf.org/doc/draft-ietf-6lo-ap-nd/)
> > > - It provides an abstract interface to the router to get routing
> > > services (already used with RIFT, RPL, see
> > > https://datatracker.ietf.org/doc/draft-ietf-roll-unaware-leaves/, and
> > > ND proxy, see
> > > https://datatracker.ietf.org/doc/draft-ietf-6lo-backbone-router/)
> > > - It solves a number of problems including Jen's, but also sleeping
> devices on
> > non-6lo networks, remote DOS against router and ND cache, and more.
> > >
> > > All in all I see it as a much needed modernization of ND to cope with
> the
> > evolutions of the network (IOT, Wi-Fi and overlays) and with the new
> needs
> > and behaviors (instant connectivity, fast roaming).
> > >
> > > All the best,
> > >
> > > Pascal
> > >
> > >> -----Original Message-----
> > >> From: 6lo <6lo-bounces@ietf.org> On Behalf Of Michael Richardson
> > >> Sent: jeudi 4 juillet 2019 02:58
> > >> To: 6lo@ietf.org; V6 Ops List <v6ops@ietf.org>rg>; 6man <6man@ietf.org>
> > >> Subject: Re: [6lo] ND cache entries creation on first-hop routers
> > >>
> > >>
> > >> Brian E Carpenter <brian.e.carpenter@gmail.com> wrote:
> > >>>> I’m interested to have a parallel discussion on where RFC 8505 can
> > >>>> not apply. In the products and use cases I’m aware of, it could,
> > >>>> since we are actually faking it by snooping ND and DHCP to achieve
> > >>>> similar but less accurate results.
> > >>
> > >>> So if you are advocating a generalisation of RFC8505 to non-6lo
> > >>> LANs, that's certainly a discussion we could have, IMHO.
> > >>
> > >> I think that it could be applied in situations of servers, such as
> > >> data centers where there are multiple tenants. (Many VM
> > >> infrastructures have shared front-end networks)
> > >>
> > >> I think that temporary addressess are not a feature in some of those
> > >> deployments that everyone wants, and thus having a registration
> > >> system is a feature.
> > >>
> > >> This does not solve the smartphone on new WIFI issue, which is a
> > >> different situation completely.
> > >>
> > >> --
> > >> ]               Never tell me the odds!                 | ipv6 mesh
> networks [
> > >> ]   Michael Richardson, Sandelman Software Works        |    IoT
> architect   [
> > >> ]     mcr@sandelman.ca  http://www.sandelman.ca/        |   ruby on
> rails    [
> > >
> > > _______________________________________________
> > > 6lo mailing list
> > > 6lo@ietf.org
> > > https://www.ietf.org/mailman/listinfo/6lo
> > >
> > >
>
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