However, many services won't let you make full use of it; e.g. last year when I tried to get multicast between my EC2 nodes, it discovered it was unsupported.
If you're only using ZeroMQ in tcp or inproc mode, it is nice, but in a pub/sub scenario you are wasting a lot of bandwidth and CPU time.
if you're not using multicast in pub sub, you're establishing individual tcp connections between nodes, it's not any different than doing N point to point communications, whereas with multicast, the data is only copied when needed, your data will fan out if that makes sense with your network topology I think if you look at the picture it'll be clear
If you're only using ZeroMQ in tcp or inproc mode, it is nice, but in a pub/sub scenario you are wasting a lot of bandwidth and CPU time.