VLAN Configuration Page

The VLAN Configuration table (Device Viewer > Switch > VLANs > VLAN Configuration) lists configuration information for each VLAN supported by the device. Configuration settings for each VLAN include the three key STP timers Hello Time, Max Age, and Fwd Delay for both the local bridge (on each VLAN, these are called Current values) and its root bridge (called Bridge values). For the current switch's VLANs, the Current Hello Time shows the time intervals between the transmission of configuration bridge PDUs (BPDUs), which flow outward from the root bridge as notifications of its root status to the other switches in the spanning tree.

The Current Max Age is the time period that an installed root's BPDU is stored by the selected switch. The Cisco default value is 20 seconds. The Current Fwd Delay value is the time period, in seconds that the current device spends in the Listening and Learning states. Among other things, it indicates how long the bridging table ages before the device switches from Forwarding mode to Listening mode. Fwd Delay also affects how quickly the switch responds to a change in topology.

The Bridge Hello Time, Bridge Max Age, and Bridge Fwd Delay values are the corresponding values dictated by the root bridge through its BPDUs to all the other bridges in the switched network, including to the current device. Most deployments require careful consideration before changing spanning tree protocol timing values, and such values should normally be modified only at the root bridge.

The figure above illustrates the principles. The root bridge advertises its Bridge Max Age = 2000, Bridge Hello Time = 200, and Bridge Fwd Delay = 1500 in the BPDUs it sends to the other switches in the network through VLAN 60. Those values are in turn used by the other switches in the network to configure their respective Max Age, Hello Time, and Fwd Delay settings (all labeled as Current in the table). In the current switch, those three STP timer values are set to the same values because they are determined by the three values communicated through the root bridge BPDUs.