HP VPN Firewall Appliances Network Management Configuration Guide

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Configuring MSTP at the CLI
Configuration guidelines
Follow these guidelines when you configure MSTP:
• Two or more spanning tree-enabled devices belong to the same MST region only if the following are
true:
{ They are configured with the same format selector (0 by default, not configurable), MST region
name, VLAN-to-instance mapping entries in the MST region, and MST region revision level.
{ They are interconnected through physical links.
• If two or more devices have been designated to be root bridges of the same spanning tree instance,
MSTP selects the device with the lowest MAC address as the root bridge.
• The values of forward delay, hello time, and max age are interdependent. Inappropriate settings of
these values might cause network flapping.
HP recommends not manually setting the spanning tree timers. Instead, you can specify the
network diameter and let spanning tree protocols automatically calculate the timers based on the
network diameter.
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)
• If the device is not enabled with BPDU guard, when a boundary port receives a BPDU from another
port, it transits into a non-boundary port. To restore its port role as a boundary port, you need to
restart the port.
Spanning tree configuration task lists
Configuration prerequisites
Before configuring a spanning tree, you must determine the spanning tree protocol to be used (STP, RSTP,
or MSTP) and plan device roles (the root bridge or leaf node).
Configuration restrictions and guidelines
• The spanning tree configurations made in system view take effect globally. Configurations made in
Ethernet interface view take effect on the interface only. Configurations made in Layer 2 aggregate
interface view take effect only on the aggregate interface. Configurations made on an aggregation
member port can take effect only after the port is removed from the aggregation group.
• After you enable a spanning tree protocol on a Layer 2 aggregate interface, the system performs
spanning tree calculation on the Layer 2 aggregate interface but not on the aggregation member
ports. The spanning tree protocol enable state and forwarding state of each selected member port
is consistent with those of the corresponding Layer 2 aggregate interface.
• Though the member ports of an aggregation group do not participate in spanning tree calculation,
the ports still reserve their spanning tree configurations for participating in spanning tree
calculation after leaving the aggregation group.