Ethernet Switches: Managed or Unmanaged?

I have seen this come up on this forum and others; as a distributor, it is also a frequently asked question. When or why should I use a managed ethernet switch? The attachment is specific to Allen-Bradley Ethernet/IP, but it can show you how to choose between a managed or unmanaged switch, and how to gauge network performance if you are already using an unmanaged switch.

Use a managed switch if you are going to be using your network for I/O or producer/consumer comms between PLC's. I/O and producers multicast on the network and you need the advanced features in a managed switch to deal with that (IGMP snooping, VLANs and QOS).

Here is a article I found on the subject from Cisco.

I think the Cisco document paints with a little bit of a broad brush. If all the components in your segregated industrial Ethernet network can handle the maximum data rate then you can still use unmanaged switches. To say that every Ethernet based I/O network needs managed switches is a bit oversimplified.

Two things I would concede are that a managed switch won't hurt you and when in doubt go managed.

Keith

kamenges said:

I think the Cisco document paints with a little bit of a broad brush.
Keith

Click to expand...

Obviously. The article is not a technical document, it is a broad generic explanation.

kamenges said:

To say that every Ethernet based I/O network needs managed switches is a bit oversimplified.
Keith

Click to expand...

I didn't say that at all. I implied that one might use managed switches on a network where PLC I/O is present. Each application has its own unique requirements and should be designed accordingly.

KyleH-

My post didn't say you said anything in particular unless you wrote the Cisco document (which you may have). My post said:

I think the Cisco document paints with a little bit of a broad brush.

Click to expand...

However, you DID write:

Originally posted by KyleH:

Use a managed switch if you are going to be using your network for I/O or producer/consumer comms between PLC's. I/O and producers multicast on the network and you need the advanced features in a managed switch to deal with that (IGMP snooping, VLANs and QOS).

Click to expand...

The post says that users need (your word, not mine) the advanced features of a managed switch in networks with a large number of multicast transmissions.

I agree with your second post that the use of managed switches is application specific. The conclusion in the Cisco document is much stronger than that statement, however.

Keith

Point taken. Probably should have phrased it better.

You are right about Cisco's statents, after all they are trying to sell a more expensive solution.

I'm writing technical specification for a machine we will be building in the near future. The recipients of this document like to pick apart words. I've gotten a little goofy with semantics lately. I need a beer.


Keith