Hi,
Carsten Bormann wrote:
On Apr 3, 2009, at 13:50, Peter Siklosi wrote:
In my mind, the simplest model would be to represent the cost as
ND in 6lowpan is (mainly) about the host-router interface.
Does the host even have to know about the way the router metric is
computed?
The host (if it wants to be just a host) should not need to know about
the routing protocol and its metrics.
I have therefore proposed the ND metric to simply be a 16-bit integer,
with a mid-range default (i.e., 0x8000 if the number is unsigned).
Routing protocols may want to define a way how to compute that integer
at a router so that multiple routers present numbers that make sense
when used together by a host. (And that may not exclude use of the value
found via ND in bootstrapping a router. Still outside the scope of ND
proper.)
BTW, standard IPv6 ND does not have such a metric for the following
stated reason:
Unlike in IPv4 Router Discovery, the Router Advertisement messages
do not contain a preference field. The preference field is not
needed to handle routers of different "stability"; the Neighbor
Unreachability Detection will detect dead routers and switch to a
working one.
[RFC 4861, p 16]. This thinking does not really seem to apply to
6lowpans very well.
I support this proposal myself, and think it is a nice solution to the
concern Peter brought up. The Multihop Information Option in
draft-ietf-nd has plenty of reserved space for such a 16-bit option.
This is also compatible with e.g. the work going on in ROLL as this
information is meant for hosts that don't have knowledge of the routing
algorithm. If a ROLL algorithm would produce such a metric - the router
would simply copy that into this field for use by hosts.
With regard to integrating this into -03 of the draft, we would need to
see some more consensus support on the list. Who else finds this useful?
- Zach
Gruesse, Carsten
(No WG chair hats included in this message.)
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