Stack Configuration and Deployment Recommendations

Feature Limitations

Stack Setup Guidelines

A stack contains a maximum of five, eight, or nine stack members depending on switch models. To ensure high forwarding performance and reliability, ensure that the number of stack members of each switch series does not exceed the recommended value. For example, the recommended number of S5700-LI switches in a stack is 2 to 5. For the recommended value of each switch series, see "Service Port Stacking Support" or "Stack Card Stacking Support".
When setting up a stack containing a mix of different switch models, follow the following rules:
- A stack cannot be set up among different switch series. For example, a stack cannot be set up among the S5700 and S6700 switches.
- A stack cannot be set up among different switch models of the same switch series. For example, a stack cannot be set up among the S5720-EI and S5720-HI switches.
- A stack can be set up among only certain different switch models of the same switch series. For example, a stack can be set up among the S5720-SI and S5720S-SI switches but not among the S5720-LI and S5720S-LI switches. For details about whether a stack can be set up among different switch models, see stack support of different switch models in Stacking Support and Version Requirements. As described in Remarks of S6720-LI and S6720S-LI Service Port Stacking Support, a stack can be set up among all S6720-LI models, among all S6720S-LI models, but not among the S6720-LI and S6720S-LI models.

Version restrictions:

When multiple switches set up a stack, member switches will synchronize the running version of the master switch. If a member switch does not support this running version, it will restart repeatedly.
In V200R009C00, if MPLS-incapable S5720-EIs exist in a stack, this stack cannot have MPLS enabled. If member devices in a stack are running MPLS services, adding MPLS-incapable S5720-EIs to the stack is not allowed.
An S5720-HI supports the stacking function since V200R009C00. When a member device in a stack is faulty and fails to restart for three consecutive times, the device attempts to roll back to a version earlier than V200R009C00 for restart. When the device restarts successfully after rolling back to a version earlier than V200R009C00, a multi-active situation may occur because the version earlier than V200R009C00 does not support the stacking function. To prevent this situation, you are advised to delete the system software earlier than V200R009C00 from member devices when using S5720-HIs to set up a stack.

MAD specifications:

You can configure a maximum of eight direct detection links for each member switch in a stack.
You can configure the relay mode on a maximum of four Eth-Trunks in a stack.
In V200R008C00 and earlier versions, you can configure a maximum of 64 Eth-Trunks on a relay agent to provide the relay function for multiple stacks. This restriction does not apply to versions later than V200R008C00.

After multiple switches form a stack, the following features cannot be configured in the stack:

Y.1731 one- and two-way frame delay measurement
N:1 VLAN Mapping
IPv6 over IPv4 tunnel
IPv4 over IPv6 tunnel
E-Trunk

When you establish a stack on the switches that support both stack card connection and service port connection, such as S5720-C-EI, note the following:

All member switches must use the same stack connection mode.
When a member switch has stack cards installed and the service port stack configuration, the switch uses the service port connection mode to establish a stack. It does not use the stack card connection mode even though a stack fails to be established in service port connection mode and stack cards are connected correctly.
A switch uses the stack card connection mode to establish a stack only when it has no service port stack configuration.
If a switch is currently using the stack card connection mode, perform the service port stack configuration on the switch before changing the stack connection mode to service port connection. After the service port stack configuration is complete, the switch uses the service port connection mode when restarting.
If a switch using the stack card connection mode has service port configuration, a smooth upgrade cannot be performed on the switch.
If a switch is currently using the service port connection mode, correctly connect stack cards and stack cables and clear the existing service port stack configuration before changing the stack connection mode to stack card connection. You can use the reset stack-port configuration command to clear the existing service port stack configuration.
When changing service port connection to stack card connection, you are advised to remove the cables connected to service ports to prevent loops.

Deployment Recommendations

Connect a stack to other network devices using an Eth-Trunk and add one port of each member switch to the Eth-Trunk.
When a stack connects to access devices, configure ports directly connected to terminals as STP edge ports to prevent STP re-calculation when the ports alternate between Up and Down states. This configuration ensures normal traffic forwarding.
If storm control needs to be configured on many ports, replace storm control with traffic suppression to save CPU resources.
If port security needs to be configured on many ports, replace port security with MAC address learning limiting to save CPU resources.
Loops may occur on a network to which a stack connects. Run the mac-address flapping action error-down command to set an interface to the error-down state when MAC address flapping is detected on the interface. This improves system processing performance and allows the peer device to detect that the interface becomes Down. Additionally, if the peer device has redundant links, traffic can be rapidly switched to a normal link.