Cisco 500 Series Administration Manual page 89

5
87
There can be up to two stack LAGs per unit.
The stack LAG can be composed of between two and eight stack ports
depending on the unit type.
Stack Port States
Stack ports can be in one of the following states:
• Down—Port operational status is down or stack port operational status is
up, but traffic cannot pass on the port.
• Active—Stack port was added to a stack LAG whose stack port
operational status is up and traffic can pass on the port and it is a member
of a stack LAG.
• Standby—Stack port operational status is up and bidirectional traffic can
pass on the port, but the port cannot be added to a stack LAG, and the port
does not transmit traffic. Possible reasons for a port being in standby are:
- Stack ports with different speeds are used to connect a single neighbor.
- One unit is connected to more than two neighboring units.
Backward Compatibility
For an explanation of the performance of a stack consisting of devices that
support stack port LAGs and devices that do not support this feature, see
Backwards Compatibility.
Physical Constraints for Stack LAGs
The following factors constrain the use of stack LAGs:
• A stack LAG must contain stack ports as described in
Table 4.
• A stack LAG must contain ports of the same speed.
• When attempting to connect a unit to a stack whose topology is not a ring/
chain (for example, trying to connect a unit to more than two neighboring
units - star topology), only two stack LAGs can be active, the remainder of
the stack ports are set to standby mode (inactive).
Recommended Stack Connections
The following tables describe the optimal way to connect units in a stack
according to the type of units in the stack.
Administration: Stack Management
Cisco 500 Series Stackable Managed Switch Administration Guide
Stack Ports
Table 1 through