Intel IXM5414E Spanning Tree Protocol STP operation, 257, Parameter Description Default value

Appendix F Troubleshooting the Spanning Tree Protocol

This appendix provides details about how the Spanning Tree Protocol and Algorithm work and describes how to troubleshoot them.

Spanning Tree Protocol (STP) operation

Spanning Tree Protocol (STP) is used in a bridged LAN environment to reduce the physical network to a stable logical topology with no data loops that still allows for the existence of redundant connections. The topology is calculated by the bridges that interconnect the individual LAN segments, and is recalculated when physical or parameter changes occur. Each bridge in the network has a unique bridge identifier, which is used to determine the root bridge of the spanning tree. Where more than one bridge on the same LAN segment offers connectivity to the root bridge, one bridge is selected as the designated bridge and one port on that bridge becomes the root port, providing access to the root bridge.

Two versions of STP are supported by the Intel® Blade Server Ethernet Switch Module IXM5414E, both of which are defined in IEEE 802.1s. The first version is IEEE 802.1D compatibility mode, set as the factory default. The second version is Rapid Reconfiguration mode, originally defined in IEEE 802.1w. Rapid Reconfiguration uses a bridging device’s ability to recognize full-duplex links (point-to-point) and ports connected to end stations (edge ports) to offer faster transitions to the forwarding state. The config spanningtree forceversion command is used to switch from IEEE8021D operation to IEEE 802.1w operation. The two versions of the protocol can interoperate within the same LAN: it is not necessary for all bridges to run the same version. Where IEEE 802.1D is mentioned in this document, you should understand that the switch is actually operating in IEEE 802.1D compatibility mode according to the protocol specified in IEEE 802.1s.

Both versions of the Spanning Tree Algorithm (STA) create a single spanning tree for an entire network within which there is at most one route between any two end stations, and will automatically reconfigure the tree when necessary. The topology created by the algorithm is influenced by user-configurable parameters, but care should be taken when changing these parameters from the factory defaults.

The following table shows the user-configurable STP parameters for the bridge.

Table 10. STP parameters – bridge

Parameter	Description	Default value
Bridge identifier	A combination of the Bridge Priority and the switch MAC	32768 + MAC
(Not user-configurable	address. The 16-bit priority parameter is concatenated
	with the 48-bit Ethernet MAC address.
except by setting the
priority as described in
this table)
Bridge Priority	A relative priority for each bridge. The lower the number	32768
	the higher the priority and the greater the likelihood of
	the bridge being elected as the root bridge.

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