broadcast instead of multicast for CARP/VRRP/keepalive

Question

In many cloud environments, multicast is blocked therefore when trying to configure CARP/VRRP customer needs to add a dedicated switch.

For example, CARP partially works if using a vSwitch from Hetzer, but the answer from the support team when asking about multicast was:

Real Multicast isn't possible inside the vSwitch. All packets will be handled like Broadcast Traffic.

Therefore wondering if BROADCAST could be used for the same purposes?

Before starting a project that maybe others already tried, I would like to know why multicast is preferred over broadcast and if it could be used as an alternative?

For learning/practice purposes, my goal would be to build a very basic health check pretty much like keepalive but that could work using broadcast instead of multicast?

Any advice?

Answer 1

Those protocols are designed to use multicast to limit the traffic to interested parties, vs. broadcast which every node must minimally process to ignore it.

Multicast is a special case of broadcast. In any network that does not understand, or choose to implement any of the logic associated with multicast, the traffic is merely seen as any other broadcast traffic. 802.11 (Wifi) is a prime example of something that does not usually apply any special logic to multicast; it's transmitted at basic-rate to every associated station just like any other broadcast.

There are plenty of older processes that use broadcast. Best practice for any new methods are to use multicast. (also because IPv6 does not have broadcast, only multicast.)