On Sat, 8 Aug 2015, Juliusz Chroboczek wrote:
As I understand the presentation that kicked off this discussion, this
becomes an issue since IPv6 relies more on multicast.
I may be confused, but I was under the impression that IPv6 uses multicast
(ND, RA) in the exact same places where IPv4 uses broadcast (ARP, DHCPv4).
As far as the 802.11 MAC is concerned, broadcast and multicast are treated
the same, so 802.11 should be just as suitable or unsuitable for IPv6 as
for IPv4.
You are correct, so this is a problem for IPv4 as well.
It's just that comparing the amount of ARP broadcast packets seen in an
IPv4 network and the amount of RA/ND packets seen in an IPv6 network, I'd
imagine the amount of multicast for IPv6 is more than 10x (just guessing)
larger unless mitigation is put in place, and then it's just larger, not
magnitudes larger.
If you miss a couple of consecutive RAs in IPv6, you abandon your prefix
and your default route. A host talking to its IPv4 gateway that has
received its address using for instance DHCPv4, usually doesn't have to do
any multicast/broadcast for hours as long as it keeps talking to/through
the gateway.
So IPv6 is a lot more sensitive to multicast packet loss compared to IPv4.
When IPv6 was designed around 1995 multicast was thought to be more
effective (because it was a middle ground between broadcast and unicast,
giving a decent tradeoff between sending to all and sending multiple
packets to whoever might be interested) compared to IPv4. This is still
now 20 years later a mindset seen widely throughout the IETF because
nobody (as far as I know) has clearly said otherwise.
--
Mikael Abrahamsson email: [email protected]
_______________________________________________
homenet mailing list
[email protected]
https://www.ietf.org/mailman/listinfo/homenet
