On Mon, 9 Mar 2015, Steinar H. Gunderson wrote:
On Mon, Mar 09, 2015 at 08:40:52AM -0700, David Lang wrote:
why does IPv6 rely on multicast?
multicast is never going to work that well on a busy wireless
network, especially one that's encrypted with a different key to
each station.
It relies on multicast the same way IPv4 relies on broadcast
(ARP, DHCP). If you like broadcast better than multicast, you're
free to simply treat it as such.
DHCP only needs to get to the dhcp server(s), not to all nodes. It's unusual for
the DHCP server to be wireless rather than wired
For ARP, it only needs to get to other wireless nodes if you are doing wireless
<-> wireless communication, which is relatively rare. And even there, the access
point can 'cheat' if it has an ARP entry for the IP and reply directly rather
than contacting every wireless node.
Explicit multicast, where the devices that want to listen to the multicast have
to tell the access point that they want to listen to a particular multicast
aren't too bad. It's the same overhead as unicast to each node. But this doesn't
scale to lots of wireless nodes using multicast.
It's fairly common for wireless networks to not allow wireless <-> wireless
communication, which cuts this off entirely.
David Lang
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