25. Spanning Tree
ROX™ v2.2 User Guide
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RuggedBackbone™ RX5000
• UNTIL RESET : The port will remain shut down until the port reset command is issued by the user.
• SPECIFY : a timeout period is specified for the port.
BPDU Timeout
Synopsis: unsigned integer
The RSTP standard does not address network security. RSTP must process every received BPDU
and take an appropriate action. This opens a way for an attacker to influence RSTP topology by
injecting RSTP BPDUs into the network. BPDU Guard protects the network from BPDUs received
by a port where RSTP-capable devices are not expected to be attached. If a BPDU is received by a
port for which the 'Edge' parameter is set to 'TRUE' or RSTP is disabled, the port will be shut down
for the time period specified by this parameter.
• DON'T SHUTDOWN : BPDU Guard is disabled.
• UNTIL RESET : The port will remain shut down until the port reset command is issued by the user.
Fast Root Failover
Synopsis: string - one of the following keywords { on-with-standard-root, off, on }
Default: on
In mesh network topologies, the standard RSTP algorithm does not guarantee deterministic network
recovery time in the case of a root switch failure. Such a recovery time is hard to calculate and
it can be different (and may be relatively long) for any given mesh topology. This configuration
parameter enables RuggedCom's enhancement to RSTP which detects a failure of the root switch
and performs some extra RSTP processing steps, significantly reducing the network recovery time
and making it deterministic.
This feature is only available in RSTP mode. In MSTP mode, the configuration parameter is ignored.
In a single ring topology, this feature is not needed and should be disabled to avoid longer network
recovery times due to extra RSTP processing. The Fast Root Failover algorithm must be supported
by all switches in the network, including the root, to guarantee optimal performance. However, it
is not uncommon to assign the root role to a switch from a vendor different from the rest of the
switches in the network. In other words, it is possible that the root might not suport the Fast Root
Failover algorithm. In such a scenario,a relaxed algorithm should be used, which tolerates the lack
of support in the root switch.
These are the supported configuration options:
• Off: Fast Root Failover algorithm is disabled and hence a root switch failure; may result in
excessive connectivity recovery time.
• On: Fast Root Failover is enabled and the most robust algorithm is used, which requires the
appropriate support in the root switch.
• On with standard root: Fast Root Failover is enabled but a relaxed algorithm is used, allowing
the use of a standard switch in the root role.
IEEE802.1w Interoperability
Synopsis: boolean
Default: true
IEEE802.1w Interoperability
Cost Style
Synopsis: string - one of the following keywords { rstp, stp }
Default: stp
The style of link costs to employ. STP uses 16-bit path costs based upon 1x10E9/link speed (4
for 1Gbps, 19 for 100 Mbps and 100 for 10 Mbps) whereas RSTP uses 32-bit costs based upon
2x10E13/link speed (20,000 for 1Gbps, 200,000 for 100 Mbps and 2,000,000 for 10 Mbps). Note
that RSTP link costs are used only when the bridge version support is set to allow RSTP and the
port does not migrate to STP.
