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Old March 12th, 2018, 09:45 AM   #1
the_msp
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Managed switch?

At what point is a managed switch recommended over a non-managed? Consider the attached architecture, is a managed switch overkill for only a handful of devices?
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Old March 12th, 2018, 10:02 AM   #2
gclshortt
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http://www.plctalk.net/qanda/showthread.php?t=63239

http://www.plctalk.net/qanda/showthread.php?t=68028

http://www.plctalk.net/qanda/showthread.php?t=93104

Each system will be different. If you need to recover fast from a disruption then use a managed switch.
The above threads may give you some additional information.
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Old March 12th, 2018, 12:08 PM   #3
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I use managed switches not for known features such as VLAN's and the like, but mostly for additional stuff like cable diagnostics, multicast/broadcast storm control, loop prevention.

Cable diagnostics is my favorite: I can remotely check each channel for shorts and open connections, including a fairly reliable indication of where a fault is located. Indispensable for remote support of local networks in harsh places where cable failure due to physical damage can happen.
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Old March 12th, 2018, 12:49 PM   #4
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With a managed switch in that architecture you could VLAN the 192.xxx.xxx.xxx and 10.xxx.xxx.xxx subnets on one switch. There are lots of good inexpensive managed switches available. I like Allied Telesis myself because they are reliable, pretty easy to configure, and inexpensive.
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Old March 12th, 2018, 01:17 PM   #5
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This is always a question of debate, I agree if the budget can afford it then a managed switch offers advanced capabilities and network segmentation that you simply cannot achieve without one. Where is the tipping that you MUST consider a managed switch, that too is probably debatable. There are lots of resources online that discusses this, however I've found a good one here at https://www.youtube.com/playlist?lis...GIFxgRW4ahZ-Cm if you are considering Allen-Bradley Stratix type switches.
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Old March 12th, 2018, 03:54 PM   #6
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I like to use Cisco switches because I've found them to be highly reliable and they also provide Cisco Network Assistant. I also have no shame in admitting that I do not, nor do I care to, know Cisco command line commands. CNA does all of that for me. I know there are some very advanced switch features that can't be configured from CNA, but I've not yet found a need to use them.
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Old March 12th, 2018, 05:03 PM   #7
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Quote:
Originally Posted by the_msp
At what point is a managed switch recommended over a non-managed? Consider the attached architecture, is a managed switch overkill for only a handful of devices?
Quote:
Originally Posted by Toine
I use managed switches not for known features such as VLAN's and the like, but mostly for additional stuff like cable diagnostics, multicast/broadcast storm control, loop prevention...
Quote:
Originally Posted by radarman
...Where is the tipping that you MUST consider a managed switch...
That tipping point is, in my IACS architectural experience, to be most importantly considered at the point in which the volume of Multicast traffic on the network cannot be processed by one or more devices that may be less Multicast tolerant. They may become flooded. This has the most detrimental effect on the performance of an IACS.

All other switch features, of which we may discuss in detail, come after this consideration. That has been my trained and on the job experience thus far. Multicast tolerance, or lack thereof, should first determine when to use a managed switch over an unmanaged switch in an IACS.

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Old March 12th, 2018, 06:58 PM   #8
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There are many very advanced reasons to use a managed switch. But, consider this very basic difference......

What is a broadcast message type? Who receives it?
What is a unicast message type? Who receives it?

Now for the most part, that is all an un-managed switch knows about. However, there is another message type that is quite common. It is called multicast. Multicast messages go to a group of subscribers. So not everyone receives it like a broadcast. But it does go to multiple targets, so not like a unicast either.

Unicast = 1 to 1
Multicast = 1 to many
Broadcast = 1 to everyone

An un-managed switch does not recognize the destination for these multicast messages. When a switch can't identify the destination for a frame, it broadcasts that frame out all ports (except the incoming port).

So with an un-managed switch, all multicast messages becomes broadcast messages potentially flooding your network with broadcasts. Then, every switch connected to that switch re-broadcasts the message.

Managed switches on the other hand can learn where the multicast message needs to go and direct it to that specify port. It does not have to broadcast it out to everyone. Now, not every managed switch does this either. It needs to support a protocol called Internet Group Management Protocol (IGMP) and might require a feature called IGMP Snooping. Neither of which is found in an un-managed switch.

I overloaded a small network of five devices that were using multicast messages by using cheap un-managed switches.

OG

Last edited by Operaghost; March 12th, 2018 at 07:01 PM.
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Old March 12th, 2018, 07:37 PM   #9
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Interesting conversation- I've often wished for an easy way to make the call since Managed AB switches take about 2 minutes to boot up, cost way more and have an infuriatingly glitchy interface.

As unmanaged switches and other devices start standardizing on Gigabit Ethernet ports, I wonder if that will that move the tipping point up before needing a managed switch?
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Old March 12th, 2018, 08:03 PM   #10
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Quote:
Originally Posted by the_msp View Post
At what point is a managed switch recommended over a non-managed? Consider the attached architecture, is a managed switch overkill for only a handful of devices?
There are different types of managed switches but putting that aside, a managed switch of some type is required when you need to communicate with the switch and maybe change a settings on it.

Rule of thumb I think is to have some kind of managed switch as soon as the network has more than one switch or a switch with 16 or more ports. Smart switches are "managed" switches with a web interface and that is your first step up from unmanaged.
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Old March 12th, 2018, 08:16 PM   #11
diat150
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Quote:
Originally Posted by Operaghost View Post
There are many very advanced reasons to use a managed switch. But, consider this very basic difference......

What is a broadcast message type? Who receives it?
What is a unicast message type? Who receives it?

Now for the most part, that is all an un-managed switch knows about. However, there is another message type that is quite common. It is called multicast. Multicast messages go to a group of subscribers. So not everyone receives it like a broadcast. But it does go to multiple targets, so not like a unicast either.

Unicast = 1 to 1
Multicast = 1 to many
Broadcast = 1 to everyone

An un-managed switch does not recognize the destination for these multicast messages. When a switch can't identify the destination for a frame, it broadcasts that frame out all ports (except the incoming port).

So with an un-managed switch, all multicast messages becomes broadcast messages potentially flooding your network with broadcasts. Then, every switch connected to that switch re-broadcasts the message.

Managed switches on the other hand can learn where the multicast message needs to go and direct it to that specify port. It does not have to broadcast it out to everyone. Now, not every managed switch does this either. It needs to support a protocol called Internet Group Management Protocol (IGMP) and might require a feature called IGMP Snooping. Neither of which is found in an un-managed switch.

I overloaded a small network of five devices that were using multicast messages by using cheap un-managed switches.

OG
yes, and keep this in mind if you are using some brands.. inet, cough... of ethernet radios on the same network. multi-cast wil kill them with the quickness.
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Old March 13th, 2018, 03:40 AM   #12
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Quote:
Originally Posted by rupej View Post
Interesting conversation- I've often wished for an easy way to make the call since Managed AB switches take about 2 minutes to boot up, cost way more and have an infuriatingly glitchy interface.
Even though the AB switches are basically modified Cisco switches, they are a serious pain to use. And about the most unreliable things I've had to deal with.

Switched to N-Tron here, for everything on the floor, and all of the Stratix weirdness went away. And much much more inexpensive then the AB switches.

And just to keep everything playing nice, we only use managed switches here, no matter the application. The small extra cost is worth it down the line.
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Old March 13th, 2018, 12:29 PM   #13
Toine
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As unmanaged switches and other devices start standardizing on Gigabit Ethernet ports, I wonder if that will that move the tipping point up before needing a managed switch?
Good question. No it will not move the tipping point (in most cases). It is often not the switch itself that suffers hard from multicast/broadcast traffic. It is the connected devices on the receiving end.

While ethernet networks are typically 1 gbps these days, the vast majority of industrial devices are 100 mbps. Even 10 mbps is still to be found in large numbers. Remember the unmanaged switches will ruthlessly forward all broadcast and multicast traffic to all devices on the network. That includes the 10mbps devices. The gbit switch just finds it easier to top up the load for these slow connection.
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Old March 13th, 2018, 03:17 PM   #14
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There are a few cases where it makes sense.

1) I've seen a lot of focus in here on multicast traffic. I've heard that's an issue on older EIP equipment, never run into any other scenarios where that's an issue. Possibly security cam type setups?

2) The second situation when you want a managed switch is if you are doing something fancy with the network. Don't want two devices on the same switch to see each other? Managed switch. Want the switch to be a DHCP server? Managed Switch. Want redundancy? Managed Switch.

3) Finally, if you want any sort of diagnostics/troubleshooting from the switch, it needs to be managed. I've seen a lot of switches that come with features like cable continuity checks, which is vital for initial build/commissioning/validation. During operation, it helps to be able to know what is plugged in where (topology detection) and to be able to signal when an error/fault is detected.

Ethernet is infrastructure. When something goes wrong, it is vital to know that the infrastructure is the cause of an issue, it isn't a process problem.
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Old March 13th, 2018, 08:40 PM   #15
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Great explanations here, I've been looking for a good answer as well to this question. There is a good video that helps explain some of this that I stumbled on that explain pretty clearly the different IP communication types...might be worth a look...https://www.youtube.com/watch?v=HHU6...RW4ahZ-Cm&t=0s
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