Moxa TN-5818-2GTXBP-HV-HV [36/36] Configuration limits of stp rstp

Communication Redundancy STP/RSTP/MSTP

4-11

Port Role

Indicates the current port role status.

Setting

Port Role Status

Factory Default

Port Role

Backup

Alternate port

Root port

Designated port

Disable

None

Configuration Limits of STP/RSTP

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

[Eq. 1]: 1 sec ≦ Hello Time ≦ 10 sec

[Eq. 2]: 6 sec ≦ Max. Age ≦ 40 sec

[Eq. 3]: 4 sec ≦ Forwarding Delay ≦ 30 sec

These three variables are further restricted by the following two inequalities:

[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:

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.

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.

Step 3: Assign a value to Forwarding Delay that satisfies the conditions