MOXA TN Series Communication Redundancy

Introduction to Communication Redundancy

Setting up Communication Redundancy on your network helps protect critical links against failure, protects against network loops, and keeps network downtime at a minimum. Communication Redundancy allows you to set up redundant loops in the network to provide a backup data transmission route in the event that a cable is inadvertently disconnected or damaged. This is a particularly important feature for industrial applications, since it could take several minutes to locate the disconnected or severed cable. For example, if the Moxa switch is used as a key communications component of a production line, several minutes of downtime could cause a big loss in production and revenue. The Moxa switch supports three different protocols to support this communication redundancy function:

• Turbo Ring and Turbo Ring V2
• Turbo Chain
• Rapid Spanning Tree and Spanning Tree Protocols (IEEE 802.1W/802.1D-2004)

When configuring a redundant ring, all switches on the same ring must be configured to use the same redundancy protocol. You cannot mix the Turbo Ring, Turbo Ring V2, and STP/RSTP protocols on the same ring. The following table lists the key differences between the features of each protocol. Use this information to evaluate the benefits of each, and then determine which features are most suitable for your network.

	Turbo Ring	Turbo Ring V2	Turbo Chain	STP	RSTP
Topology	Ring	Ring	Chain	Ring, Mesh	Ring, Mesh
Recovery Time	< 300 ms	< 20 ms	< 20 ms	Up to 30 sec.	Up to 5 sec

NOTE
Most of Moxa’s managed switches now support three proprietary Turbo Ring protocols:

1. Turbo Ring refers to the original version of Moxa’s proprietary redundant ring protocol, which has a recovery time of under 300 ms.
2. Turbo Ring V2 refers to the new generation Turbo Ring, which has a recovery time of under 20 ms.
3. Turbo Chain is a new Moxa proprietary protocol with unlimited flexibility that allows you to construct any type of redundant network topology. The recovery time is under 20 ms.

In this manual, we use the terminology Turbo Ring and Turbo Ring V2 to differentiate between rings configured for one or the other of these protocols.

Gigabit Ethernet Redundant Ring Capability (< 50 ms)
Ethernet has become the default data communications medium for industrial automation applications. In fact, Ethernet is often used to integrate video, voice, and high-rate industrial application data transfers into one network. Moxa switches come equipped with a redundant Gigabit Ethernet protocol called Gigabit Turbo Ring. With Gigabit Turbo Ring, if any segment of the network gets disconnected, your automation system will be back to normal in less than 300 ms (Turbo Ring) or 50 ms (Turbo Ring V2).

 

NOTE
Port trunking and Turbo Ring can be enabled simultaneously to form a backbone. Doing so will increase the bandwidth of the backbone, and also provide redundancy. For example, suppose that two physical ports, 1 and 2, are trunked to form trunk group Trk1, and then Trk1 is set as one Turbo Ring path. If port 1 gets disconnected, the remaining trunked port, port 2, will share the traffic. If ports 1 and 2 are both disconnected, the Turbo Ring will create a backup path within 300 ms.

 Turbo Ring

The Turbo Ring Concept
Moxa developed the proprietary Turbo Ring protocol to optimize communication redundancy and achieve a faster recovery time on the network. The Turbo Ring and Turbo Ring V2 protocols identify one switch as the master of the network, and then automatically block packets from traveling through any of the network’s redundant loops. In the event that one branch of the ring gets disconnected from the rest of the network, the protocol automatically readjusts the ring so that the part of the network that was disconnected can reestablish contact with the rest of the network.

Setting up “Turbo Ring” or “Turbo Ring V2”

1. Select any two ports as redundant ports.
2. Connect the redundant ports to form the Turbo Ring.

The user does not need to configure any of the switches as the master to use Turbo Ring or Turbo Ring V2. If none of the switches in the ring is configured as the master, then the protocol will automatically assign master status to one of the switches. In fact, the master is only used to identify which segment in the redundant ring acts as the backup path. In the following subsections, we explain how the redundant path is selected for rings configured for Turbo Ring, and Turbo Ring V2.

Determining the Redundant Path of a “Turbo Ring” Ring
In this case, the redundant segment (i.e., the segment that will be blocked during normal operation) is determined by the number of switches in the ring, and where the ring master is located.

When the Number of Switches in the Turbo Ring is Even  If there are 2N switches (an even number) in the “Turbo Ring” ring, then the backup segment is one of the two segments connected to the (N+1)st switch (i.e., the switch directly opposite the master).

When the Number of Switches in the Turbo Ring is Odd 

If there are 2N+1 switches (an odd number) in the “Turbo Ring” ring, with switches and segments labeled counterclockwise, then segment N+1 will serve as the backup path. For the example shown here, N=1, so that N+1=2.

Determining the Redundant Path of a “Turbo Ring V2” Ring
For a “Turbo Ring V2” ring, the backup segment is the segment connected to the 2nd redundant port on the master. See Configuring “Turbo Ring V2” in the Configuring “Turbo Ring” and “Turbo Ring V2” section below.

Ring Coupling Configuration
For some systems, it may not be convenient to connect all devices in the system to create one BIG redundant ring, since some devices could be located in a remote area. For these systems, Ring Coupling can be used to separate the devices into different smaller redundant rings, but in such a way that they can still communicate with each other.

ATTENTION
In a VLAN environment, the user must set Redundant Port, Coupling Port, and Coupling Control Port to join all VLANs, since these ports act as the backbone to transmit all packets of different VLANs to different switches.

Ring Coupling for a “Turbo Ring” Ring 

To configure the Ring Coupling function for a “Turbo Ring” ring, select two switches (e.g., Switch A and B in the above figure) in the ring, and another two switches in the adjacent ring (e.g., Switch C and D). Decide which two ports in each switch are appropriate to be used as coupling ports, and then link them together. Next, assign one switch (e.g., Switch A) to be the coupler and connect the coupler’s coupling control port with Switch B (for this example). The coupler switch (i.e., Switch A) will monitor switch B through the coupling control port to determine whether or not the coupling port’s backup path should be recovered.

Ring Coupling for a “Turbo Ring V2” Ring 

Note that the ring coupling settings for a “Turbo Ring V2” ring are different from a “Turbo Ring” ring. For Turbo Ring V2, Ring Coupling is enabled by configuring the Coupling Port (Primary) on Switch B, and the Coupling Port (Backup) on Switch A only. You do not need to set up a coupling control port, so that a “Turbo Ring V2” ring does not use a coupling control line.

The Coupling Port (Backup) on Switch A is used for the backup path, and connects directly to an extra network port on Switch C. The Coupling Port (Primary) on Switch B monitors the status of the main path, and connects directly to an extra network port on Switch D. With ring coupling established, Switch A can activate the backup path as soon as it detects a problem with the main path.

ATTENTION
Ring Coupling only needs to be enabled on one of the switches serving as the Ring Coupler. The Coupler must designate different ports as the two Turbo Ring ports and the coupling port.

NOTE
You do not need to use the same switch for both Ring Coupling and Ring Master.

Dynamic Ring Coupling (DRC) Configuration (applies only to “Turbo Ring V2”)
Moxa’s switch supports Turbo Ring V2 with Dynamic Ring Coupling (DRC), which is an innovative inter-consist network redundancy technology. It not only supports Ring Coupling (RC), which enables fast network recovery during link failures, but also automatically assigns the active coupler switch on each train consist when train consist sequences are changed, added, or removed. This not only prevents looping and broadcast storms, but also reduces additional configuration time and possible errors caused by user configuration, enhancing network communication reliability and efficiency.

Turbo Ring V2 with DRC (Dyanmic Ring Coupling) 

Turbo Ring V2 with DRC Diagram 2
Note that the dynamic ring coupling settings are only supported by “Turbo Ring V2”.

1. DRC Group 1 requires one or two switches as members of a ring (Diagram 1: Left side of ring A, B, C; or Diagram 2: Left side of ring A, C, and right side of ring B).
2. DRC Group 2 requires one or two switches as members of a ring (Diagram 1: Right side of ring A, B, C; or Diagram 2: Right side of ring A, C and left side of ring B).
3. Ring Coupler – Scenario 1:
   Linking all members of DRC group 1 to the member of the another ring DRC group 2 (Diagram 1: The left side DRC group 1 of ring C coupled to right side DRC group 2 of ring B); orlinking all members of DRC group 1 to the member of the another ring DRC group 1 (Diagram 2: The right side of DRC group 1 of ring B coupled to the left side of DRC group 1 of ring C); or no connection to DRC group 1 (Diagram 1: The left side DRC group 1 of ring A).
4. Ring Coupler – Scenario 2:
   By linking all members of DRC group 2 to the member of the another ring DRC group 1 (Diagram 1: The right side DRC group 2 of ring A coupler to left side DRC group 1 of ring B) or by linking all members of DRC group 2 to the member of the another ring DRC group 2 (Diagram 2: The right side DRC group 2 of ring A coupler to left side DRC group 2 of ring B) or no connection of the DRC group 2 (Diagram 2: The right side DRC group 2 of ring C)
5. After all cable connections complete, the DRC protocol will start convergence and automatically assign one DRC group of the ring as Active DRC group.

ATTENTION
Although redundancy protocols (e.g. Turbo Ring, Turbo Ring v2) can be enabled on ports that support bypass functionality, we don’t recommend enabling redundancy protocols on these ports as this may affect the intended convergence times (e.g. 50 ms for Turbo Ring v2). This will be particularly noticeable when a device suffers from a power failure.

NOTE
By pass function is used to apply on linear topology only.

Dual-Ring Configuration (applies only to “Turbo Ring V2”)
The dual-ring option provides another ring coupling configuration, in which two adjacent rings share one switch. This type of configuration is ideal for applications that have inherent cabling difficulties.

Dual-Ring for a “Turbo Ring V2” Ring

Dual-Homing Configuration (applies only to “Turbo Ring V2”)
The dual-homing option uses a single Ethernet switch to connect two networks. The primary path is the operating connection, and the backup path is a back-up connection that is activated in the event that the primary path connection fails.

Dual-Homing for a “Turbo Ring V2” Ring

Configuring “Turbo Ring” and “Turbo Ring V2”
Use the Communication Redundancy page to select Turbo Ring, Turbo Ring V2, or Turbo Chain. Note that configuration pages for these three protocols are different.

Configuring “Turbo Ring”

Explanation of “Current Status” Items 

• Now Active
  It shows which communication protocol is in use: Turbo Ring, Turbo Ring V2, RSTP, or none.
• Master/Slave
  It indicates whether or not this switch is the Master of the Turbo Ring. (This field appears only when Turbo Ring or Turbo Ring V2 modes are selected.)

NOTE
The user does not need to set the master to use Turbo Ring. If master is not set, the Turbo Ring protocol will assign master status to one of the switches in the ring. The master is only used to determine which segment serves as the backup path.

Redundant Ports Status (1st Port, 2nd Port)
Ring Coupling Ports Status (Coupling Port, Coupling Control Port) The “Ports Status” indicators show Forwarding for normal transmission, Blocking if this port is connected to a backup path and the path is blocked, and Link down if there is no connection.

Explanation of “Settings” Items 

Redundancy Protocol 

Setting	Description	Factory Default
Turbo Ring	Select this item to change to the Turbo Ring configuration page.	None
Turbo Ring V2	Select this item to change to the Turbo Ring V2 configuration page.
Turbo Ring V2 with DRC (Dynamic Ring Coupling)	Select this item to change to the Turbo Ring V2 with DRC configuration page.
Turbo Chain	Select this item to change to the Turbo Chain configuration page.
RSTP (IEEE 802.1W/ 802.1D-2004)	Select this item to change to the RSTP configuration page.
None	Ring redundancy is not active.

Set as Master 

Setting	Description	Factory Default
Enabled	Select this switch as the Master.	Not checked
Disabled	Do not select this switch as the Master.

Redundant Ports

Setting	Description	Factory Default
1st Port	Select any port of the switch to be one of the redundant ports.	See the following table
2nd Port	Select any port of the switch to be one of the redundant ports.	See the following table

	Default 1st Port	Default 2nd Port
EDS-400A Series EDS-505A/508A/516A Series	The second from the last port	The last port
EDS-518A Series	Port G1	Port G2
EDS-510A Series	Port G2	Port G3
EDS-608/616	The third port of the last module	The fourth port of the last module
EDS-611/619	Port G2	Port G3
EDS-728/828 Series	Port 1-1	Port 1-2
IKS-6726 Series	without Gigabit Ethernet module: Port 1-1 with Gigabit Ethernet module: Port 4-1	without Gigabit Ethernet module: Port 1-2 with Gigabit Ethernet module: Port 4-2
IKS-G6524/G6824 Series ICS-G7526/G7528/ G7826/G7828 Series	The second from the last port	The last port
TN-4500A Series TN-5500A Series TN-5800 Series	The second from the last non-bypass Ethernet port number	The last non-bypass Ethernet port number

NOTE
The Relay Bypass function has the potential to interrupt the normal operation of a Turbo Ring. For this reason, the Turbo Ring features cannot used on Relay Bypass Ports.

Enable Ring Coupling 

Setting	Description	Factory Default
Enable	Select this switch as a Coupler.	Not checked
Disable	Do not select this switch as a Coupler.

Coupling Port

Setting	Description	Factory Default
Coupling Port	Select any port of the switch to be the coupling port	See the following table

Coupling Control Port

Setting	Description	Factory Default
Coupling Control Port	Select any port of the EDS to be the coupling control port	See the following table

Default Coupling Port 

	Default Coupling Port	Default Coupling Control Port
EDS-400A Series EDS-505A/508A/516A Series	The fourth from the last port	The third from the last port
EDS-518A Series	Port 15	Port 16
EDS-510A Series	Port 7	Port G1
EDS-608/616	The second port of the last module	The first port of the last module
EDS-611/619	Port G1	The last port of the last module
EDS-728/828 Series	Port 1-3	Port 1-4
IKS-6726 Series	without Gigabit Ethernet module: Port 1-3 with Gigabit Ethernet module: Port 1-1	without Gigabit Ethernet module: Port 1-4 with Gigabit Ethernet module: Port 1-2
IKS-G6524/G6824 Series ICS-G7526/G7528/ G7826/G7828 Series	The fourth from the last port	The third from the last port
TN-5500/TN-5500A Series TN-5800 Series	The fourth from the last Fast Ethernet port number	The third from the last Fast Ethernet port number

Configuring “Turbo Ring V2” 

 

 

NOTE
When using the Dual-Ring architecture, users must configure settings for both Ring 1 and Ring 2. In this case, the status of both rings will appear under “Current Status.”

Explanation of “Current Status” Items 

• Now Active
  It shows which communication protocol is in use: Turbo Ring, Turbo Ring V2, Turbo Chain, RSTP, or none.
• Ring 1/2—Status
  It shows Healthy if the ring is operating normally, and shows Break if the ring’s backup link is active.
• Ring 1/2—Master/Slave
  It indicates whether or not this EDS is the Master of the Turbo Ring. (This field appears only when Turbo Ring or Turbo Ring V2 modes are selected.)

NOTE
The user does not need to set the master to use Turbo Ring. If master is not set, the Turbo Ring protocol will assign master status to one of the EDS units in the ring. The master is only used to determine which segment serves as the backup path.

• Ring 1/2—1st Ring Port Status
• Ring 1/2—2nd Ring Port Status

The “Ports Status” indicators show Forwarding for normal transmission, Blocking if this port is connected to a backup path and the path is blocked, and Link down if there is no connection.
Coupling—Mode

• It indicates either None, Dual Homing, or Ring Coupling.
• Coupling—Coupling Port status
• It indicates either Primary, or Backup.

Explanation of “Settings” Items 

Redundancy Protocol

Setting	Description	Factory Default
Turbo Ring	Select this item to change to the Turbo Ring configuration page.	None
Turbo Ring V2	Select this item to change to the Turbo Ring V2 configuration page.
Turbo Ring V2 with DRC (Dynamic Ring Coupling)	Select this item to change to the Turbo Ring V2 with DRC configuration page.
Turbo Chain	Select this item to change to the Turbo Chain configuration page
RSTP (IEEE 802.1W/ 802.1D-2004)	Select this item to change to the RSTP configuration page.
None	Ring redundancy is not active

Enable Ring 1 

Setting	Description	Factory Default
Enabled	Enable the Ring 1 settings	Not checked
Disabled	Disable the Ring 1 settings	Not checked

Enable Ring 2* 

Setting	Description	Factory Default
Enabled	Enable the Ring 2 settings	Not checked
Disabled	Disable the Ring 2 settings

NOTE
You should enable both Ring 1 and Ring 2 when using the Dual-Ring architecture.

Set as Master

Setting	Description	Factory Default
Enabled	Select this EDS or TN switch as the Master.	Not checked
Disabled	Do not select this EDS or TN switch as the Master.

Redundant Ports 

Setting	Description	Factory Default
1st Port	Select any port of the EDS or TN switch to be one of the redundant ports.	See the following table
2nd Port	Select any port of the EDS or TN switch to be one of the redundant ports.	See the following table

Default Ports

	Default 1st Port	Default 2nd Port
EDS-400A Series EDS-505A/508A/516A Series	The second from the last port	The last port
EDS-518A Series	Port G1	Port G2
EDS-510A Series	Port G2	Port G3
EDS-608/616	The third port of the last module	The fourth port of the last module
EDS-611/619	Port G2	Port G3
EDS-728/828 Series	Port 1-1	Port 1-2
IKS-6726 Series	without Gigabit Ethernet module: Port 1-1 with Gigabit Ethernet module: Port 4-1	without Gigabit Ethernet module: Port 1-2 with Gigabit Ethernet module: Port 4-2
IKS-G6524/G6824 Series ICS-G7526/G7528/ G7826/G7828 Series	The second from the last port	The last port
TN-5500/TN-5500A Series TN-5800 Series	The second from the last Fast Ethernet port number	The last Fast Ethernet port number

NOTE
For EDS-600 Series switches, there are certain restrictions on which ports can be used as ring ports.

• You may use any two of the non-Gigabit ports as the ring ports; however, the two ring ports for a particular switch must be on the same module.
• If you need to use Gigabit ports as ring ports, you must use the second and third Gigabit ports (G2 and G3) as the ring ports (but do NOT use G1).

Enable Ring Coupling

Setting	Description	Factory Default
Enable	Select this EDS or TN switch as a Coupler.	Not checked
Disable	Do not select this EDS or TN switch as a Coupler.

Coupling Mode

Setting	Description	Factory Default
Dual Homing	Select this item to change to the Dual Homing configuration page	See the following table
Ring Coupling (backup)	Select this item to change to the Ring Coupling (backup) configuration page	See the following table
Ring Coupling (primary)	Select this item to change to the Ring Coupling (primary) configuration page	See the following table

Default Dual Homing Ports

	Default Dual Homing (Primary)	Default Dual Homing (Backup)
EDS-400A Series EDS-505A/508A/516A Series	The fourth from the last port	The third from the last port
EDS-518A Series	Port 15	Port 16
EDS-510A Series	Port G1	Port G2
EDS-608/616	The first port of the first module	The second port of the first module
EDS-611/619	Port G1	The last port of the last module
EDS-728/828 Series	N/A	N/A
IKS-6726 Series	without Gigabit Ethernet module: Port 1-5 with Gigabit Ethernet module: Port 1-3	without Gigabit Ethernet module: Port 1-6 with Gigabit Ethernet module: Port 1-4
IKS-G6524/G6824 Series ICS-G7526/G7528/ G7826/G7828 Series	The fourth from the last port	The third from the last port
TN-5500/TN-5500A Series TN-5800 Series	The first port number	The first port number

NOTE
The Turbo Ring DIP Switches located on the outer casing of EDS series switches can be used to configure the switches’ Turbo Ring protocols.  If you use the web interface, console interface, or Telnet interface to enable the Turbo Ring DIP Switches, and then set DIP Switch 4 on the switch’s outer casing to the ON position, you will not be able to use the web interface, console interface, or Telnet interface to change the status of the DIP Switch. In this case, the Communication Redundancy settings will be grayed out in the web browser as shown in the following figure:

 

Configuring “Turbo Ring V2” with Dynamic Ring Coupling (DRC) 

Explanation of “Ring Status” Items 

• Now Active
  It shows which redundant protocol is in use: Turbo Ring, Turbo Ring V2, RSTP, MSTP, Turbo Ring V2 with DRC (Dynamic Ring Coupling) or none.
• Ring Master ID
  It indicates the smallest MAC address of the device in the ring.
• Status
  The “Status” indicator shows Healthy for normal transmission of a ring, Break if the ring is incomplete or there is no connection.
• Master/Slave
  It indicates whether or not this switch is the Master of the Turbo Ring V2 with DRC. (This field appears only when Turbo Ring, Turbo Ring V2 or Turbo Ring V2 with DRC modes are selected.)

1st Ring Port Status
The “Ring Ports Status” indicators show Forwarding for normal transmission, Blocked if this port is connected to a backup path and the path is blocked, and Link down if there is no connection.

2nd Ring Port Status
The “Ports Status” indicators show Forwarding for normal transmission, Blocked if this port is connected to a backup path and the path is blocked, and Link down if there is no connection.

Explanation of “DRC Status” Items 

Coupling Group
The “Coupling Group” indicators show Active for taking the responsibility to maintain the coupling links, Inactive if the other group of the ring is Active status already.

Coupling Port Status
The “Coupling Ports Status” indicators show Port number + Forwarding for normal transmission. If the switch is the ring master, it will show the status of two coupling groups using MAC address + Port number + Link up. If the coupling port has no connection, it shows MAC address + Port number + Link down.

Explanation of “Ring Settings” Items 

Redundancy Protocol 

Setting	Description	Factory Default
Turbo Ring	Select this item to change to the Turbo Ring configuration page.	None
Turbo Ring V2	Select this item to change to the Turbo Ring V2 configuration page.
Turbo Ring V2 with DRC (Dynamic Ring Coupling)	Select this item to change to the Turbo Ring V2 with DRC configuration page.
Turbo Chain	Select this item to change to the Turbo Chain configuration page
RSTP (IEEE 802.1W/ 802.1D-2004)	Select this item to change to the RSTP configuration page.

Set as Master 

Setting	Description	Factory Default
Enabled	Select this switch as Master	Disabled
Disabled	Select this switch as Slave or if no master in the ring, it may choose the switch with smallest MAC address as Master (Candidate Master)

Redundant Ports

Setting	Description	Factory Default
1st Port	Select any port of the switch to be one of the redundant ports.	See the following table
2nd Port	Select any port of the switch to be one of the redundant ports.	See the following table

	Default 1st Port	Default 2nd Port
TN-5508A/10A Series	7	8
TN-5516A/18A Series	15	16

DRC Settings 

Setting	Description	Factory Default
Group1/Coupling Ports	Select any port of the switch to be one of the coupling group 1 port and choose auto, primary, backup as the port role	Port number: None Role: Auto
Group2/Coupling Ports	Select any port of the switch to be one of the coupling group 2 port and choose auto, primary, backup as the port role	Port number: None Role: Auto

Turbo Chain

The Turbo Chain Concept
Moxa’s Turbo Chain is an advanced software technology that gives network administrators the flexibility of constructing any type of redundant network topology. When using the “chain” concept, you first connect the Ethernet switches in a chain and then simply link the two ends of the chain to an Ethernet network, as illustrated in the following figure. Turbo Chain can be used on industrial networks that have a complex topology. If the industrial network uses a multi-ring architecture, Turbo Chain can be used to create flexible and scalable topologies with a fast media-recovery time.

Setting Up Turbo Chain 

 

 

1. Select the Head switch, Tail switch, and Member switches.
2. Configure one port as the Head port and one port as the Member port in the Head switch, configure one port as the Tail port and one port as the Member port in the Tail switch, and configure two ports as Member ports in each of the Member switches.
3. Connect the Head switch, Tail switch, and Member switches as shown in the above diagram.

The path connecting to the Head port is the main path, and the path connecting to the Tail port is the backup path of the Turbo Chain. Under normal conditions, packets are transmitted through the Head Port to the LAN network. If any Turbo Chain path is disconnected, the Tail Port will be activated so that packet transmission can continue.

Configuring “Turbo Chain”
Head Switch Configuration Member Switch Configuration  Tail Switch Configuration  Explanation of “Current Status” Items 

Now Active
It shows which communication protocol is in use: Turbo Ring, Turbo Ring V2, RSTP, Turbo Chain, or None. The “Ports Status” indicators show Forwarding for normal transmission, Blocked if this port is connected to the Tail port as a backup path and the path is blocked, and Link down if there is no connection.

Explanation of “Settings” Items 

Redundancy Protocol 

Setting	Description	Factory Default
Turbo Ring	Select this item to change to the Turbo Ring configuration page.	None
Turbo Ring V2	Select this item to change to the Turbo Ring V2 configuration page.
Turbo Chain	Select this item to change to the Turbo Chain configuration page
RSTP	Select this item to change to the RSTP configuration page.
None	Ring redundancy is not active

Role

Setting	Description	Factory Default
Head	Select this switch as Head Switch	Member
Member	Select this switch as Member Switch
Tail	Select this switch as Tail Switch

Head Role 

Setting	Description	Factory Default
Head Port	Select any port of the EDS to be the head port.	See the following table
Member Port	Select any port of the EDS to be the member port.	See the following table

Member Role 

Setting	Description	Factory Default
1st Member port	Select any port of the EDS to be the 1st member port	See the following table
2nd Member port	Select any port of the EDS to be the 2nd member port	See the following table

Tail Role

Setting	Description	Factory Default
Tail Port	Select any port of the EDS to be the tail port.	See the following table
Member Port	Select any port of the EDS to be the member port.	See the following table

Head Role	Default Head Port	Default Member Port
EDS-400A Series EDS-505A/508A Series	The second from the last port	The last port
EDS-518A Series	Port G1	Port G2
EDS-510A Series	Port G2	Port G3
EDS-608/616	The third port of the last module	The fourth port of the last module
EDS-611/619	Port G2	Port G3
EDS-728/828 Series	Port 1-1	Port 1-2
IKS-6726 Series	without Gigabit Ethernet module: Port 1-1 with Gigabit Ethernet module: Port 4-1	without Gigabit Ethernet module: Port 1-2 with Gigabit Ethernet module: Port 4-2
IKS-G6524/G6824 Series ICS-G7526/G7528/ G7826/G7828 Series	The second from the last port	The last port

Member Role	Default 1st Member Port	Default 2nd Member Port
EDS-400A Series EDS-505A/508A Series	The second from the last port	The last port
EDS-518A Series	Port G1	Port G2
EDS-510A Series	Port G2	Port G3
EDS-608/616	The third port of the last module	The fourth port of the last module
EDS-611/619	Port G2	Port G3
EDS-728/828 Series	Port 1-1	Port 1-2
IKS-6726 Series	without Gigabit Ethernet module: Port 1-1 with Gigabit Ethernet module: Port 4-1	without Gigabit Ethernet module: Port 1-2 with Gigabit Ethernet module: Port 4-2
IKS-G6524/G6824 Series ICS-G7526/G7528/ G7826/G7828 Series	The second from the last port	The last port

Tail Role	Default Tail Port	Default Member Port
EDS-400A Series EDS-505A/508A/516A Series	The second from the last port	The last port
EDS-518A Series	Port G1	Port G2
EDS-510A Series	Port G2	Port G3
EDS-608/616	The third port of the last module	The fourth port of the last module
EDS-611/619	Port G2	Port G3
EDS-728/828 Series	Port 1-1	Port 1-2
IKS-6726 Series	without Gigabit Ethernet module: Port 1-1 with Gigabit Ethernet module: Port 4-1	without Gigabit Ethernet module: Port 1-2 with Gigabit Ethernet module: Port 4-2
IKS-G6524/G6824 Series ICS-G7526/G7528/ G7826/G7828 Series	The second from the last port	The last port

NOTE
For EDS-600 Series switches, there are certain restrictions on which ports can be used as ring ports.

• You may use any two of the non-Gigabit ports as the ring ports; however, the two ring ports for a particular switch must be on the same module.
• If you need to use Gigabit ports as ring ports, you must use the second and third Gigabit ports (G2 and G3) as the ring ports (but do NOT use G1).

STP/RSTP/MSTP

The STP/RSTP/MSTP Concept
Spanning Tree Protocol (STP) was designed to help reduce link failures on a network, and provide provide an automatic means of avoiding loops. This is particularly important for networks that have a complicated architecture, since unintended loops in the network can cause broadcast storms. Moxa switches’ STP feature is disabled by default. To be completely effective, you must enable RSTP/STP on every Moxa switch connected to your network. Rapid Spanning Tree Protocol (RSTP) implements the Spanning Tree Algorithm and Protocol defined by IEEE 802.1D-2004. RSTP provides the following benefits:

• The topology of a bridged network will be determined much more quickly compared to STP.
• RSTP is backward compatible with STP, making it relatively easy to deploy. For example:
• Defaults to sending 802.1D style BPDUs if packets with this format are received.
• STP (802.1D) and RSTP (802.1w) can operate on different ports of the same switch, which is particularly helpful when switch ports connect to older equipment such as legacy switches.

You get essentially the same functionality with RSTP and STP. To see how the two systems differ, see the Differences between STP and RSTP section in this chapter.

NOTE
The STP protocol is part of the IEEE Std 802.1D, 2004 Edition bridge specification. The following explanation uses “bridge” instead of “switch.”

What is STP?
STP (802.1D) is a bridge-based system that is used to implement parallel paths for network traffic. STP uses a loop-detection process to:

• Locate and then disable less efficient paths (i.e., paths that have a lower bandwidth).
• Enable one of the less efficient paths if a more efficient path fails.

 

If STP is enabled, it will detect duplicate paths and prevent, or block, one of the paths from forwarding traffic. In the following example, STP determined that traffic from LAN segment 2 to LAN segment 1 should flow through bridges C and A since this path has a greater bandwidth and is therefore more efficient.

What happens if a link failure is detected? As shown in next figure, the STP process reconfigures the network so that traffic from LAN segment 2 flows through bridge B.STP will determine which path between each bridged segment is most efficient, and then assign a specific reference point on the network. When the most efficient path has been identified, the other paths are blocked. In the previous 3 figures, STP first determined that the path through bridge C was the most efficient, and as a result, blocked the path through bridge B. After the failure of bridge C, STP re-evaluated the situation and opened the path through Bridge B. STP will determine which path between each bridged segment is most efficient, and then assign a specific reference point on the network. When the most efficient path has been identified, the other paths are blocked. In the previous 3 figures, STP first determined that the path through bridge C was the most efficient, and as a result, blocked the path through bridge B. After the failure of bridge C, STP re-evaluated the situation and opened the path through Bridge B.

How STP Works 

When enabled, STP determines the most appropriate path for traffic through a network. The way it does this is outlined in the sections below.

STP Requirements
Before STP can configure the network, the system must satisfy the following requirements:

• All bridges must be able to communicate with each other. The communication is carried out using Bridge Protocol Data Units (BPDUs), which are transmitted in packets with a known multicast address.
• Each bridge must have a Bridge Identifier that specifies which bridge acts as the central reference point, or Root Bridge, for the STP system—bridges with a lower Bridge Identifier are more likely to be designated as the Root Bridge. The Bridge Identifier is calculated using the MAC address of the bridge and a priority defined for the bridge. For example, the default priority setting of Moxa switches is 32768.
• Each port has a cost that specifies the efficiency of each link. The efficiency cost is usually determined by the bandwidth of the link, with less efficient links assigned a higher cost.

STP Calculation 

The first step of the STP process is to perform calculations. During this stage, each bridge on the network transmits BPDUs. The following items will be calculated:

• Which bridge should be the Root Bridge. The Root Bridge is the central reference point from which the network is configured.
• The Root Path Costs for each bridge. This is the cost of the paths from each bridge to the Root Bridge.
• The identity of each bridge’s Root Port. The Root Port is the port on the bridge that connects to the Root Bridge via the most efficient path. In other words, the port connected to the Root Bridge via the path with the lowest Root Path Cost. The Root Bridge, however, does not have a Root Port.
• The identity of the Designated Bridge for each LAN segment. The Designated Bridge is the bridge with the lowest Root Path Cost from that segment. If several bridges have the same Root Path Cost, the one with the lowest Bridge Identifier becomes the Designated Bridge. Traffic transmitted in the direction of the Root Bridge will flow through the Designated Bridge. The port on this bridge that connects to the segment is called the Designated Bridge Port.

STP Configuration
After all of the bridges on the network agree on the identity of the Root Bridge, and all other relevant parameters have been established, each bridge is configured to forward traffic only between its Root Port and the Designated Bridge Ports for the respective network segments. All other ports are blocked, which means that they will not be allowed to receive or forward traffic.

STP Reconfiguration
Once the network topology has stabilized, each bridge listens for Hello BPDUs transmitted from the Root Bridge at regular intervals. If a bridge does not receive a Hello BPDU after a certain interval (the Max Age time), the bridge assumes that the Root Bridge, or a link between itself and the Root Bridge, has ceased to funtion. This will trigger the bridge to reconfigure the network to account for the change. If you have configured an SNMP trap destination, when the topology of your network changes, the first bridge to detect the change will send out an SNMP trap.

Differences between STP, RSTP, and MSTP 

RSTP is similar to STP, but includes additional information in the BPDUs that allow each bridge to confirm that it has taken action to prevent loops from forming when it decides to enable a link to a neighboring bridge. Adjacent bridges connected via point-to-point links will be able to enable a link without waiting to ensure that all other bridges in the network have had time to react to the change. The main benefit of RSTP is that the configuration decision is made locally rather than network-wide, allowing RSTP to carry out automatic configuration and restore a link faster than STP.

STP and RSTP spanning tree protocols operate without regard to a network’s VLAN configuration, and maintain one common spanning tree throughout a bridged network. Thus, these protocols map one loop-free, logical topology on a given physical topology. MSTP uses VLANs to create multiple spanning trees in a network, which significantly improves network resource utilization while maintaining a loop-free environment.

STP Example
The LAN shown in the following figure has three segments, with adjacent segments connected using two possible links. The various STP factors, such as Cost, Root Port, Designated Bridge Port, and Blocked Port are shown in the figure.

 

• Bridge A has been selected as the Root Bridge, since it was determined to have the lowest Bridge Identifier on the network.
• Since Bridge A is the Root Bridge, it is also the Designated Bridge for LAN segment 1. Port 1 on Bridge A is selected as the Designated Bridge Port for LAN Segment 1.
• Ports 1 of Bridges B, C, X, and Y are all Root Ports since they are nearest to the Root Bridge, and therefore have the most efficient path.
• Bridges B and X offer the same Root Path Cost for LAN segment 2. However, Bridge B was selected as the Designated Bridge for that segment since it has a lower Bridge Identifier. Port 2 on Bridge B is selected as the Designated Bridge Port for LAN Segment 2.
• Bridge C is the Designated Bridge for LAN segment 3, because it has the lowest Root Path Cost for LAN Segment 3:
  • The route through bridges C and B costs 200 (C to B=100, B to A=100)
  • The route through bridges Y and B costs 300 (Y to B=200, B to A=100)
• The Designated Bridge Port for LAN Segment 3 is port 2 on bridge C.

Using STP on a Network with Multiple VLANs 
IEEE Std 802.1D, 1998 Edition, does not take into account VLANs when calculating STP information—the calculations only depend on the physical connections. Consequently, some network configurations will result in VLANs being subdivided into a number of isolated sections by the STP system. You must ensure that every VLAN configuration on your network takes into account the expected STP topology and alternative topologies that may result from link failures.

The following figure shows an example of a network that contains VLANs 1 and 2. The VLANs are connected using the 802.1Q-tagged link between switch B and Switch C. By default, this link has a port cost of 100 and is automatically blocked because the other switch-to-switch connections have a port cost of 36 (18+18). This means that both VLANs are now subdivided—VLAN 1 on switches A and B cannot communicate with VLAN 1 on switch C, and VLAN 2 on switches A and C cannot communicate with VLAN 2 on switch B.

To avoid subdividing VLANs, all inter-switch connections should be made members of all available 802.1Q VLANs. This will ensure connectivity at all times. For example, the connections between switches A and B, and between switches A and C, should be 802.1Q tagged and carrying VLANs 1 and 2 to ensure connectivity.

Configuring STP/RSTP
The following figures indicate which Spanning Tree Protocol parameters can be configured. A more detailed explanation of each parameter follows.

At the top of this page, the user can check the Current Status of this function. For RSTP, you will see:
Now Active:
It shows which communication protocol is being used—Turbo Ring, RSTP, or neither.

Root/Not Root
This field only appears when RSTP mode is selected. The field indicates whether or not this switch is the Root of the Spanning Tree (the root is determined automatically). At the bottom of this page, the user can configure the Settings of this function. For RSTP, you can configure:

Redundancy Protocol

Setting	Description	Factory Default
Turbo Ring	Select this item to change to the Turbo Ring configuration page.	None
RSTP (IEEE 802.1W/1D)	Select this item to change to the RSTP configuration page.	None

Bridge priority

Setting	Description	Factory Default
Numerical value selected by user	Increase this device’s bridge priority by selecting a lower number. A device with a higher bridge priority has a greater chance of being established as the root of the Spanning Tree topology.	32768

Forwarding Delay (sec.)

Setting	Description	Factory Default
Numerical value input by user	The amount of time this device waits before checking to see if it should change to a different state.	15

Hello time (sec.) 

Setting	Description	Factory Default
Numerical value input by user	The root of the Spanning Tree topology periodically sends out a “hello” message to other devices on the network to check if the topology is healthy. The “hello time” is the amount of time the root waits between sending hello messages.	2

Max. Age (sec.)

Setting	Description	Factory Default
Numerical value input by user	If this device is not the root, and it has not received a hello message from the root in an amount of time equal to “Max. Age,” then this device will reconfigure itself as a root. Once two or more devices on the network are recognized as a root, the devices will renegotiate to set up a new Spanning Tree topology.	20

Enable STP per Port 

Setting	Description	Factory Default
Enable/Disable	Select to enable the port as a node on the Spanning Tree topology.	Disabled

NOTE
We suggest not enabling the Spanning Tree Protocol once the port is connected to a device (PLC, RTU, etc.) as opposed to network equipment. The reason is that it will cause unnecessary negotiation.

Setting	Description	Factory Default
Auto	If the port does not receive a BPDU within 3 seconds, the port will be in the forwarding state. Once the port receives a BPDU, it will start the RSTP negotiation process.	Auto
Force Edge	The port is fixed as an edge port and will always be in the forwarding state
False	The port is set as the normal RSTP port

Port Priority 

Setting	Description	Factory Default
Numerical value selected by user	Increase this port’s priority as a node on the Spanning Tree topology by entering a lower number.	128

Port Cost 

Setting	Description	Factory Default
Numerical value input by user	Input a higher cost to indicate that this port is less suitable as a node for the Spanning Tree topology.	200000

Root Status
Indicates the Root bridge of the Spanning Tree.
Redundancy Protocol

Setting	Description	Factory Default
RSTP (IEEE 802.1W/1D)	Select the RSTP configuration page.	None
Turbo Ring	Select the Turbo Ring configuration page.	None
Turbo Ring V2	–	–
Turbo Chain	–	–
MSTP (IEEE 802.1s)	Select the MSTP configuration page.	None

Forwarding Delay (sec.)

Setting	Description	Factory Default
Numerical value input by user (4-30)	The amount of time this device waits before checking to see if it should change to a different state.	15

Hello time (sec.)

Setting	Description	Factory Default
Numerical value input by user (1-10)	The root of the Spanning Tree topology periodically sends out a “hello” message to other devices on the network to check if the topology is healthy. The “hello time” is the amount of time the root waits between sending hello messages.	2

Max Hops 

Setting	Description	Factory Default
Numerical value input by user (6-40)	The MSTP maximum hops value is the maximum number of hops in the region. Configure the maximum number of hops a BPDU can be forwarded in the MSTP region.	20

Max. Age (sec.)

Setting	Description	Factory Default
Numerical value input by user (6-40)	If this device is not the root, and it has not received a hello message from the root in an amount of time equal to “Max. Age,” then this device will reconfigure itself as a root. Once two or more devices on the network are recognized as a root, the devices will renegotiate to set up a new Spanning Tree topology.	20

Revision Level

Setting	Description	Factory Default
Numerical value input by user (0-65535)	The MSTP revision level is the revision number of the configuration. All EDS switches in an MSTP region must be configured with the same revision level.	0

Region Name 

Setting	Description	Factory Default
Character string	The region name helps define the logical boundary of the network. All EDS switches in an MSTP region must be configured with the same name.	MSTP

Config Confirm

Setting	Description	Factory Default
Enable/Disable	Clicking “Activate” button will only save the MSTP settings temporarily; you can select to enable this configuration to activate the MSTP settings during the operation.	Disabled

Instance ID

Setting	Description	Factory Default
Numerical value selected by user	Within each MST region, the MSTP maintains multiple spanning-tree instances. A common and internal spanning tree (CIST) is a collection of the following: ISTs in each MST region, and the common spanning tree (CST) that interconnects the MST regions, and a single spanning tree. All other MST instances are numbered from 1 to 15.	Cist

Vlan Mapping 

Setting	Description	Factory Default
Numerical value input by user (1-4094)	Configure which VLAN ID is mapped to the multiple spanning- tree instances.	None

Bridge priority

Setting	Description	Factory Default
Numerical value selected by user	Increase this device’s bridge priority by selecting a lower number. A device with a higher bridge priority has a greater chance of being established as the root of the Spanning Tree topology.	32768

Enable

Setting	Description	Factory Default
Enable/Disable	Select to enable the port as a node on the Multiple Spanning Tree topology.	Disabled

Port Priority 

Setting	Description	Factory Default
Numerical value selected by user	Increase this port’s priority as a node on the Multiple Spanning Tree topology by entering a lower number.	128

Port Cost

Setting	Description	Factory Default
Numerical value input by user	Input a higher cost to indicate that this port is less suitable as a node for the Multiple Spanning Tree topology. Use the default value (0) to use port speed in the auto port cost.	0

Oper Cost
Indicates the cost of the path to the other bridge from this transmitting bridge at the specified port.

Edge

Setting	Description	Factory Default
Enable/Disable	Select to enable the port as the edge port for the Multiple Spanning Tree topology.	Disabled

Configuration Limits of STP/RSTP 

The Spanning Tree Algorithm places limits on three of the configuration items described previously:

1. [Eq. 1]: 1 sec ≦ Hello Time ≦ 10 sec
2. [Eq. 2]: 6 sec ≦ Max. Age ≦ 40 sec
3. [Eq. 3]: 4 sec ≦ Forwarding Delay ≦ 30 sec
   These three variables are further restricted by the following two inequalities:
   
4. [Eq. 4]: 2 x (Hello Time + 1 sec) ≦ Max. Age ≦ 2 x (Forwarding Delay – 1 sec)

Moxa EDS-600’s firmware will alert you immediately if any of these restrictions are violated. For example, setting Hello Time = 5 sec, Max. Age = 20 sec, and Forwarding Delay = 4 sec does not violate Eqs. 1 through 3, but does violate Eq. 4, since in this case,
2 x (Hello Time + 1 sec) = 12 sec, and 2 x (Forwarding Delay – 1 sec) = 6 sec.
You can remedy the situation in many ways. One solution is simply to increase the Forwarding Delay value to at least 11 sec.

HINT: Perform the following steps to avoid guessing:

1. Step 1: Assign a value to Hello Time and then calculate the left most part of Eq. 4 to get the lower limit of Max. Age.
2. Step 2: Assign a value to Forwarding Delay and then calculate the right most part of Eq. 4 to get the upper limit for Max. Age.
3. Step 3: Assign a value to Forwarding Delay that satisfies the conditions

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• Information in this document is subject to change without notice and does not represent a commitment on the part of Moxa.
• Moxa provides this document as is, without warranty of any kind, either expressed or implied, including, but not limited to, its particular purpose. Moxa reserves the right to make improvements and/or changes to this manual, or to the products and/or the programs described in this manual, at any time.
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Documents / Resources

MOXA TN Series Communication Redundancy [pdf] User Manual TN Series Communication Redundancy, TN Series, Communication Redundancy, Redundancy

References

• User Manual