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Hi David, great question! This is often a debate and it looks like you’ve got a good handle on when a managed switch should be considered. I would add a couple of important features you get with managed switches that you won’t get with unmananged:
- Port Mirroring (for troubleshooting traffic)
- Port Diagnostics
- SNMP (for switch management)
Like you said, things like I/O, motion and particularly HMI traffic can push a lot of traffic on your network – especially if you are going with cheaper alternatives (non-Rockwell).
That said, you can consider unmanaged switches under the following conditions:
- In isolated networks – networks are segregated from each other and not interconnected via a router or other means. The need for multicast traffic mitigation is greatly reduced.
- If you are using only Rockwell products – Rockwell products are well designed and can tolerate high load multicast traffic where IGMP has not been employed.
- Multicast capability for every node must be greater than the sum of all multicast traffic in the network. For example, the 1756-ENBT module can tolerate 5000 packets per second. This is a sum of multicast from joined and non-joined group members.
Of course, without doing traffic analysis (via a managed switch) knowing what kind of multicast you have is next to impossible. I hope this has been somewhat helpful and that other will chime in.