Specifications

1-4
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
78-11380-07
Chapter 1 Overview
Features
Note For additional descriptions of the management interfaces, see the “Management Options”
section on page 1-7.
Redundancy
• HSRP for command-switch redundancy
• UniDirectional link detection (UDLD) on all Ethernet ports for detecting and disabling
unidirectional links on fiber-optic interfaces caused by incorrect fiber-optic wiring or port faults
• IEEE 802.1D Spanning Tree Protocol (STP) for redundant backbone connections and loop-free
networks. STP has these features:
– Per-VLAN Spanning Tree (PVST) for balancing load across VLANs
– Per-VLAN Rapid Spanning Tree (PVRST) for balancing load across VLANs (available only
with the EI)
– UplinkFast, cross-stack UplinkFast, and BackboneFast for fast convergence after a
spanning-tree topology change and for achieving load balancing between redundant uplinks,
including Gigabit uplinks and cross-stack Gigabit uplinks
• IEEE 802.1S Multiple STP (MSTP) for grouping VLANs into a spanning-tree instance, and
providing for multiple forwarding paths for data traffic and load balancing (available only with
the EI)
• IEEE 802.1W Rapid STP (RSTP) for rapid convergence of the spanning tree by immediately
transitioning root and designated ports to the forwarding state (available only with the EI)
• Optional spanning-tree features available in the PVST, PVRST, 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
Note The switch supports up to 64 spanning-tree instances.
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, and Catalyst 2950SX-24 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)