Cisco Systems OL-4580-01 manual Configuring Spanning-Tree Bridging for the CSS, C H A P T E R

C H A P T E R 2

Configuring Spanning-Tree Bridging for the CSS

The CSS supports configuration of Spanning-Tree Protocol (STP) bridging. Spanning-tree bridging detects, and then prevents, loops in the network. Use the bridge command to configure global spanning-tree bridging options for the CSS, such as bridge aging time, forward delay time, hello time interval, and maximum age. Make sure 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 STP, 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-tree loop is detected, the Catalyst switch goes into blocking mode on one of its looped ports.

	Cisco Content Services Switch Routing and Bridging Configuration Guide
OL-4580-01		2-1