Subject: RE: (ngtrans) wg last call for 6to4anycast-00.txt

From: "Christian Huitema" <[email-masked]>
Date: Mon, 18 Dec 2000 10:20:13 -0800

Keith,

Keith,

I understand your concern. Tony and I actually debated the point of
using ND or not during the design of the proposal, and I also had a
number of informal conversations on the subject with various members of
the group, but I failed to document this in the current draft.

The ND alternative would be to use the anycast address for discovering
the nearest relay, and then to build a "regular" association with this
relay. It can be argued that using ND will be more a more standard way
to do routing, that with a regular association failures will be easier
to detect, and also that nailing the default connection to a specific
6to4 relay router will avoid any transient failure caused by the routing
protocol. On the other hand, there are many arguments against this type
of association:

* Using ND to discover the next hop router may be in line with the
generic IPv6 architecture, but is actually not in line with the specific
software written for 6to4, in which the IPv4 next hop is derived
algorithmically from the IPv6 destination address. In any case,
maintaining ND associations for each 6to4 router that they serve will
increase the load of 6to4 relay routers.

* If the default connection is nailed to a specific 6to4 relay router,
the 6to4 router must actively monitor that router, detect failures, and
then try to find a secondary router, which will only be possible if
routing tables have been updated. In contrast, with a pure anycast
tunnelling solution, the packets will be routed to the functioning 6to4
relay router as soon as the routing tables have been updated.

* After a failure of the nearest 6to4 relay router, if we use ND, the
default connection will be nailed to a back-up 6to4 relay router, and
will only be nailed back to the nearest 6to4 relay router if the back-up
fails. In contrast, with a pure anycast tunnelling solution, the packets
will always be routed to the nearest available 6to4 relay router.

Another line of argument is that the use of ND between routers is not
entirely defined, and that using ND in this scenario is potentially more
complex and more error-prone than just forwarding the packets to a well
known anycast address. In the absence of a clear-cut advantage for the
ND solution, it is preferable to chose the simpler alternative, pure
anycat tunnelling.

-- Christian Huitema