Hi Francis and Ohta-san.
----- Original Message -----
From: Francis Dupont <Francis(_dot_)Dupont(_at_)enst-bretagne(_dot_)fr>
Date: Wednesday, November 10, 2004 2:15 am
Subject: Re: Why, technically, MIP and IPv6 can't be deployed
In your previous mail you wrote:
> Could you describe why exactly IPv6 can't run on the (layer
2?) WLAN
> infrastructure?
That ND extensively, without any valid reason to do so, use
multicast, which is not acknowledged at WLAN L2, means IPv6
or its ND is unreliable over congested WLAN. If multicast
ND packet is lost by congestion, it is not retransmitted by L2.
=> Masataka san, your argument is right (I saw 40% lost rate
on multicast over IEEE 802.11b) but it applies to IPv4 (ARP
uses broadcast) too...
I understand this is the case, but we can still modify the hosts
to do something about it.
Multicast or Broadcast are necessary if we want generic
address discovery in IPv4/6 networks. Obviously we'll have problems
with MAC level acknowledgements for messages received by multiple
hosts.
RFC 2461 (as described by a recent individual submission of mine)
allow Neighbour cache entries to be created with reliable
802.11 MAC transport (unicast toDS=0,toDS=1, multicast toDS=1)
where there is only one MAC recipient in the contention domain.
This may be done to preemptively place neighbour cache entries
into first hop routers.
Since Ohta-san mentioned MIPv6 here, the router becomes the most
relevant peer for neighbour discovery.
The mechanism doesn't require protocol modification, and is
available today (If it's practically helpful, and implemented).
It may need some further documentation though.
Greg Daley
draft-daley-ipv6-preempt-nd-00.txt
This has been implemented in <40 lines of C in the Linux Kernel.
Results, while early are fairly promising.
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