Use IPv6 multicast with IPv4 anycast?

[Harvie]

I have cluster with IPv4 unicast adresses, but i've found my network can only handle IPv6 multicast traffic... Is it possible to use IPv6 multicast with IPv4 unicast setup?

Problem is that my networking hardware don't have IGMP querier (IPv4), but it has MLD querier (IPv6). Unfortunately IGMP snooping can't be disabled... But i haven't deployed IPv6 anycast yet. So it would make sense to use IPv6 for multicast only, until i get full IPv6 support in my network.

[jfriesse]

@Harvie No it is not possible. I would also recommend to reconsider usage of multicast because it is known to have a problems (mostly switches related) and udpu/knet has comparable or better speed.

[ReyRen]

@Harvie In the corosync 3, the nodelist is required whatever use the udp,udpu or Kent. So multicast might be obsoleted.

[Harvie]

@jfriesse @ReyRen really? I am using corosync which is part of proxmox and in proxmox docs they strongly reccomend to use multicast. Well they use 2.4.4-dirty version... I was thinking that the muticast is used in order to drop packet count for large clusters, because when N nodes "ping" each other, it's almost N^2 packets every millisecond or so... But i don't really know how this works internally...

[jfriesse]

@Harvie Really. In corosync 1.x udp was recommended because udpu was really not ready yet. With 2.x we are recommending udpu, because of huge amount of support requests mostly related to bad/incorrectly configured switches. And with 3.x we recommend knet (which is unicast or sctp) and made nodelist required.

Also you are technically right, corosync 3 has no rrp. But corosync 3 with knet can use up-to 8 links in rrp like fashion (so it's actually much better). I'm also not that sure proxmox guys stick with 2.x for long time, you can ask @Fabian-Gruenbichler.

You are right that multicast should be more effective and it's true from perspective of sending node to switch. But receiving packets is same story no matter if unicast or multicast is used.

[Harvie]

But corosync 3 with knet can use up-to 8 links in rrp like fashion (so it's actually much better).

Yes. I've realized this and therefore deleted my comment. Thanks for clarification...