HP VPN Firewall Appliances Network Management Configuration Guide
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Configuring spanning tree timers
The following timers are used for spanning tree calculations:
• Forward delay—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 transits from the
discarding state to the forwarding state. The port transits its state after a forward delay timer expires,
to make sure the state transition of the local port remains 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 during 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, the device uses the max age parameter to determine
whether a configuration BPDU received by a port has expired. If it has, a new spanning tree
calculation process starts. The max age timer does not take effect on other MSTIs except the CIST.
To prevent network instability, make sure the timer settings 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. Instead, HP recommends that you specify the
network diameter and using the automatically calculated timers based on the network diameter. If the
network diameter uses the default value, the timers also use their default values.
Configure timers on the root bridge only. Timer settings on the root bridge apply to all devices on the
entire switched network.
Configuration guidelines
• The length of the forward delay timer is related to the network diameter of the switched network. The
larger the network diameter is, the longer the forward delay time should be. If the forward delay
timer is too short, temporary redundant paths might occur. If the forward delay timer is too long,
network convergence might take a long time. HP recommends that you use the default setting.
• An appropriate hello time setting enables the device to promptly detect link failures on the network
without using excessive network resources. If the hello time is too long, the device will mistake
packet loss as a link failure and trigger a new spanning tree calculation process. If the hello time is
too short, the device will frequently send the same configuration BPDUs, which add the device
burden and waste network resources. HP recommends that you use the default setting.
• If the max age timer is too short, the device will frequently launch spanning tree calculation and
might mistake network congestion as a link failure. If the max age timer is too long, the device might
fail to detect link failures and launch spanning tree calculations promptly, reducing the auto-sensing
capability of the network. HP recommends that you use the default setting.
Configuration procedure
To configure the spanning tree timers:
Ste
p
Command
Remarks
1. Enter system view.
system-view N/A
2. Configure the forward
delay timer.
stp timer forward-delay time
Optional.
Use one of the commands.
The default setting is 15 seconds.