Configuring The Network Diameter Of A Switched Network; Configuring Spanning Tree Timers - HP A5830 Configuration Manual

Configuring the network diameter of a switched network

Any two terminal devices in a switched network are connected through a specific path composed of a
series of devices. The network diameter is the number of devices on the path composed of the most
devices. The network diameter is a parameter that indicates the network size. A bigger network diameter
indicates a larger network size.
To configure the network diameter of a switched network:
Step...
1. Enter system view
2. Configure the network diameter of the
switched network (in STP/RSTP/MSTP mode)
3. Configure the network diameter of the
switched network (in PVST mode)
Based on the network diameter you configured, the system automatically sets an optimal hello time,
forward delay, and max age for the device.
In STP/RSTP/MSTP mode, each MST region is considered as a device and the configured network
diameter is effective only for the CIST (or the common root bridge), but not for MSTIs.
In PVST mode, the network diameter configuration is effective on the root bridge only.

Configuring spanning tree timers

The following timers are used for spanning tree calculation:
Forward delay

It is the delay time for port state transition. To prevent temporary loops on a network, the spanning tree
sets an intermediate port state, the learning state, before it transitions from the discarding state to the
forwarding state, and requires that the port transitions its state after a forward delay timer to make sure
that the state transition of the local port keeps synchronized with the peer.
Hello time

The device detects whether a link failure has occurred with the hello time interval. The spanning tree
sends a configuration BPDU every hello time interval. If the device receives no configuration BPDUs within
the hello time interval, it recalculates the spanning tree.
Max age

In the CIST of an MSTP network or each VLAN of a PVST network, the device uses the max age
parameter to determine whether a configuration BPDU received by a port has expired. If a port receives a
configuration BPDU that has expired, that MSTI must be re-calculated. The max age timer is ineffective for
MSTIs.
To avoid frequent network changes, be sure that the settings of the hello time, forward delay and max
age timers meet the following formulas:
2 × (forward delay – 1 second)  max age

Max age  2 × (hello time + 1 second)

HP recommends not setting the spanning tree timers manually. Instead, specify the network diameter and
let spanning tree protocols automatically calculate the timers based on the network diameter. If the
network diameter uses the default value, the timers also use their default values.
Command...
system-view
stp bridge-diameter diameter
stp vlan vlan-list bridge-
diameter diameter
67
Remarks
—
Required
Use either command
7 by default