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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
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Chapter 1 Overview
Features
• 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
