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Allegro Multimeter Manual

STP module

The STP module processes Spanning Tree Protocol (STP) traffic and stores the history of all seen Root Bridges including information about these.

STP Statistics

Section titled “STP Statistics”

Current STP configuration

Section titled “Current STP configuration”

The first table shows the specification of the current configuration. That is the information derived from the last seen STP packet. If there are two specifications competing (for example the root bridge), the entries may jitter.

The shown informations are:

  • Root bridge MAC: This is the MAC address of the current root bridge, also called root bridge system ID. This is not necessarily the MAC address you use to connect to the management interface of the bridge/switch, but probably pretty similar to this one.

  • Root Bridge Priority: This is a priority value (default is 0x8000), of the (root) switch/bridge that can be set by the user. The switch/bridge with the lowest priority value becomes root bridge. If the priority values of two switches are the same, the MAC addresses will be compared.

  • Designated bridge MAC: This is the MAC address of the bridge that announced respectively forwarded the current configuration. If the last packet crossed no other switches after it has been sent from the root bridge, this MAC address is the same as the root bridge MAC.

  • Designated bridge Priority: This is a priority value (default is 0x8000), of the (designated) switch/bridge that can be set by the user. The switch/bridge with the lowest priority value becomes root bridge. If the priority values of two switches are the same, the MAC addresses will be compared.

  • Seen STP packets: This is the number of all seen STP packets.

  • Costs for root path: These are the costs to reach the root bridge. The costs from one switch/bridge to another can be defined in the interface of the switch/bridge.

  • Message age: A generated STP frame starts with Message age 0. Every time this frame crosses a bridge the age is increased by 1.

  • Max age: This is the maximum message age until a sent STP packet is discarded respectively invalid.

  • Time between config messages (Hello Time): This specifies how often configuration messages (also called BPDU frames) are sent.

  • Forward delay: This is the time that is spent in the listening and learning state.

  • Share of STP with this root port: This is the percentaged share of STP traffic with this root port. I.e. that is the quotient of the number of STP packets with the root port of this configuration divided by the number of all seen STP packets.

  • STP version: This is the STP version that was used in the last seen STP packet. Common versions are:

    • 0: STP (Spanning Tree Protocol)
    • 2: RSTP (Rapid Spanning Tree Protocol)

Root bridge history

Section titled “Root bridge history”

This table contains the MAC addresses of all seen root bridges including their last configuration and the last time they were announced as root bridge in an accounted packet.