Cisco Systems OL-4580-01 Configuring Spanning-Tree Bridging for a VLAN or a Trunked Interface

Chapter 1 Configuring Interfaces and Circuits

Configuring Interfaces

Configuring Spanning-Tree Bridging for a VLAN or a Trunked Interface

The CSS supports configuration of Spanning-Tree Protocol (STP) bridging for an Ethernet interface in a VLAN or for a trunked Ethernet interface. Spanning-tree bridging is used to detect, and then prevent, loops in the network. You can define the bridge spanning-tree path cost, priority, and state for an Ethernet interface or for a trunked Ethernet interface. Ensure you configure the spanning-tree bridging parameters the same on all switches running STP in the network.

Note When connecting a Cisco Catalyst switch to a CSS using an 802.1Q trunk and the Spanning-Tree Protocol, the Catalyst runs a spanning-tree instance for each VLAN. When you configure an 802.1Q trunk on an Ethernet interface for the Catalyst switch, the bridge protocol data units (BPDUs) are tagged with the corresponding VLAN ID and the destination MAC address changes from the standard 01-80-C2-00-00-00 to the proprietary 01-00-0c-cc-cc-cd. This modification allows Cisco switches operating in a non-Cisco (a mix of other vendors) 802.1Q trunk environment to maintain spanning-tree states for all VLANs. Although the CSS maintains a spanning-tree instance for each VLAN as well, the CSS uses the standard 01-80-C2-00-00-00 destination MAC address for all BPDUs (tagged or untagged). When you connect a Cisco Catalyst switch to a CSS over an 802.1Q trunk, the result is that neither switch recognizes the other's BPDUs, and both assume root status. If a spanning-treeloop is detected, the Catalyst switch goes in to blocking mode on one of its looped ports.

This section includes the following topics:

•Configuring Spanning-Tree Bridge Pathcost

•Configuring Spanning-Tree Bridge Port Priority

•Configuring Spanning-Tree Bridge State

For details about globally configuring spanning-tree bridging parameters for the CSS (such as bridge aging time, forward delay time, hello time interval, and maximum age), refer to Chapter 2, Configuring Spanning-Tree Bridging for the CSS.

	Cisco Content Services Switch Routing and Bridging Configuration Guide
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