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WLAN (was Re: IPv6 Host Configuration of Recursive DNS Server)



Dear all;

The problem is rather generic than DNS configuration. But...

I know ND is wrong. That is, I know it is wrong to have generic
link protocols ignoring link specific properties and has been
pondering on how such protocols suffer.

I just recently noticed that WLAN (802.11*) is not very good at
supporting ND (nor DHCP nor any broadcast/multicast protocol).

Because WLAN use CSMA/CA, it needs ACK for reliable transmission
by confirming that each packet reaches its destination without
collision.

However, with broadcast/multicast packets, there is no ACK for
an obvious reason.

If WLAN is lightly loaded, it is not a serious problem.

However, if WLAN is heavily loaded, ND (and DHCP and any broadcast/
multicast protocol) works poorly. Note that MIPv6 works poorly
too. 

Still, management beacon frames are transmitted frequently
and expected to carry information in a long run.

So, it is possible to piggyback broadcast/multicast part
of address resolution and autoconfiguration (maybe and
routing) in reserved fields of beacon frames.

Though  it is possible to use some data frame frequently
transmitted like beacon frams, it make the already congested
WLAN worse.

Anyway, the fundamental mistake is to try not to have link
specific ways to perform address resolution and autoconfiguration.

DHCP simply needs link specific ways of DHCP discover.

ND needs, IMHO, a lot more.

Note that modifying WLAN protocol to use PIFS is not enough
unless combined with frequent transmission.

						Masataka Ohta


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