ZyXEL Communications GS1900 Apply, Cancel, Max Age, seconds, Priority, Max Hops, Hello Time, CIST Instance, Forward Delay, Tx Hold Count, 6 to 40 seconds, As a general rule:

Chapter 25 Configuration: Spanning Tree

Figure 128 Configuration > Spanning Tree > CIST

The following table describes the labels in this screen.

Table 110 Configuration > Spanning Tree > CIST

LABEL	DESCRIPTION
CIST Instance
Priority	Configure priority of CIST bridge ID.
	Priority is part of bridge ID, used for CIST root bridge selection.
Max Hops	Enter a maximum number of hops value. The value can be between 1 and 40.
Forward Delay	This is the maximum time (in seconds) a switch will wait before changing states. This delay
	is required because every switch must receive information about topology changes before it
	starts to forward frames. In addition, each port needs time to listen for conflicting
	information that would make it return to a blocking state; otherwise, temporary data loops
	might result. The allowed range is 4 to 30 seconds.
	As a general rule:

	Note: 2 * (Forward Delay - 1) >= Max Age >= 2 * (Hello Time + 1)
Max Age	This is the maximum time (in seconds) a switch can wait without receiving a BPDU before
	attempting to reconfigure. All switch ports (except for designated ports) should receive
	BPDUs at regular intervals. Any port that ages out STP information (provided in the last
	BPDU) becomes the designated port for the attached LAN. If it is a root port, a new root
	port is selected from among the switch ports attached to the network. The allowed range is
	6 to 40 seconds.
Tx Hold Count	Enter a transmission hold count value. The value can be between 1 and 10.
Hello Time	This is the time interval in seconds between BPDU (Bridge Protocol Data Units)
	configuration message generations by the root switch. The allowed range is 1 to 10
	seconds.
Apply	Click Apply to save the changes.
Cancel	Click Cancel to discard the changes.

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GS1900 Series User’s Guide