Stride Industrial Ethernet Switches User Manual 2nd Ed. Rev. B
Chapter 2 - Managed Switch Quick Start
Why might you need a Managed Switch?
Enhanced traffic filtering:
An unmanaged switch will filter out many packets from an end device that a hub would not
but there are still many types of packets that an unmanaged switch cannot determine what
to do with and must forward on to all ports. Whenever a device receives a packet that is not
specifically targeted to that device, there is a certain amount of processing time that takes
away from other important tasks that the device may really need to be spending time on.
These ‘unintentional’ packets also get in the way of the packets that are intended for that
device. This hurts the determinism of a process. A managed switch can help with this in
several different ways:
• Multicast Filtering (IGMP): It is common in a control system to see a large amount of Multicast
packets. These packets cannot be filtered out by an unmanaged switch. The Stride managed switch
can intelligently ‘learn’ whether certain Multicast packets should be sent to the devices on its ports
and will filter them or not filter them appropriately.
• VLANs: A VLAN is a logical way to separate networks in ways that used to require physical
separation. Because of existing network infrastructure or for ease of wiring (and reduced cost), it
may be difficult to physically separate networks that need separation due to the type of packets that
are on them. Setting up VLANs can simplify the setup for these situations.
• Traffic Priority (QoS/CoS): Some traffic may be more important to a specific device than other
traffic. Using the Quality of Service feature, the Stride switch can apply tags to a packet coming
into the switch to give that packet a higher priority going to another switch. The last switch will
then remove the tag before sending the packet to the device. It can also use the tags applied to the
packets by the devices themselves if they support this.
Troubleshooting:
As Ethernet messaging becomes more of the standard for communications between devices
in a control system, it may become more necessary to gain visibility to these types of
communications. With hubs, it was possible to see the messages between devices because
hubs broadcast every packet to all ports. Unmanaged switches took away this capability as
they filter unicast packets to only the intended physical ports. Managed switches can help
with this by utilizing the Port Mirroring feature. The Stride managed switch can also give
you visibility in to the type of packets that are being sent across the switch by viewing the
Network Statistics page in the configuration.
• Port Mirroring: With the Port Mirroring feature you simply specify which ports’ data you want to
view and where to send that data. Plug your PC into that port and use Ethernet sniffing software
(such as Wireshark) and you can now see the data being sent back and forth.
• Network Statistics: By looking at what kind of packets that are coming in and out of the switch,
you can determine what action needs to be taken to make your network work better. If you see a
lot of Multicast traffic, utilize the Multicast Filtering feature. If there are lots of broken packets,
troubleshoot the wiring to determine where the problem lies.
Redundancy:
The downside of any Ethernet switch is the simple fact that it is another electronic
component in the system that could be subject to failure. There is also the risk that as a
network grows and more switches are added to it, a ‘ring’ may accidentally be created causing
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