Cisco 2950 Software Configuration Guide - Page 39

Chapter 1 Overview Features 78-11380-10 • IEEE 802.1s Multiple Spanning Tree Protocol (MSTP) for grouping VLANs into a spanning-tree instance and for providing multiple forwarding paths for data traffic and load balancing and rapid per-VLAN Spanning-Tree plus (rapid-PVST+) based on the IEEE 802.1w Rapid Spanning Tree Protocol (RSTP) for rapid convergence of the spanning tree by immediately transitioning root and designated ports to the forwarding state • Optional spanning-tree features available in the PVST+, rapid PVST+, and MSTP modes: - Port Fast for eliminating the forwarding delay by enabling a port to immediately transition from the blocking state to the forwarding state - BPDU guard for shutting down Port Fast-enabled ports that receive BPDUs - BPDU filtering for preventing a Port Fast-enabled port from sending or receiving BPDUs - Root guard for preventing switches outside the network core from becoming the spanning-tree root - Loop guard for preventing alternate or root ports from becoming designated ports because of a failure that leads to a unidirectional link VLAN Support • The switches support 250 port-based VLANs for assigning users to VLANs associated with appropriate network resources, traffic patterns, and bandwidth Note The Catalyst 2950-12, Catalyst 2950-24, Catalyst 2950SX-24, Catalyst 2950SX-48-SI, and Catalyst 2950T-48-SI switches support only 64 port-based VLANs. • The switch supports up to 4094 VLAN IDs to allow service provider networks to support the number of VLANs allowed by the IEEE 802.1Q standard (available only with the EI) • IEEE 802.1Q trunking protocol on all ports for network moves, adds, and changes; management and control of broadcast and multicast traffic; and network security by establishing VLAN groups for high-security users and network resources • VLAN Membership Policy Server (VMPS) for dynamic VLAN membership • VLAN Trunking Protocol (VTP) pruning for reducing network traffic by restricting flooded traffic to links destined for stations receiving the traffic • Dynamic Trunking Protocol (DTP) for negotiating trunking on a link between two devices and for negotiating the type of trunking encapsulation (802.1Q) to be used • Voice VLAN for creating subnets for voice traffic from Cisco IP Phones • VLAN 1 minimization to reduce the risk of spanning-tree loops or storms by allowing VLAN 1 to be disabled on any individual VLAN trunk link. With this feature enabled, no user traffic is sent or received. The switch CPU continues to send and receive control protocol frames. Security • Bridge protocol data unit (BPDU) guard for shutting down a Port Fast-configured port when an invalid configuration occurs • Protected port option for restricting the forwarding of traffic to designated ports on the same switch • Password-protected access (read-only and read-write access) to management interfaces (CMS and CLI) for protection against unauthorized configuration changes • Port security option for limiting and identifying MAC addresses of the stations allowed to access the port • Port security aging to set the aging time for secure addresses on a port Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide 1-5