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Catalyst 3750 SwitchSoftware Configuration Guide
OL-8550-09
Chapter1 Overview
Features
DHCP Snooping enhancement to support the selection of a fixed string-based format for the
circuit-id sub-option of the Option 82 DHCP field
Increased support for LLPD-MED by allowing the switch to grant power to the power device (PD),
based on the power policy TLV request
Availability and Redundancy Features
HSRP for command switch and Layer3 router redundancy
Enhanced object tracking, which separates the tracking mechanism from HSRP and creates a
separate, standalone tracking process that can be used by processes other than HSRP
Automatic stack master re-election for replacing stack masters that become unavailable (failover
support)
The newly elected stack master begins accepting Layer2 traffic in less than 1 second and Layer 3
traffic between 3to 5 seconds.
Cross-stack EtherChannel for providing redundant links across the switch stack
UniDirectional Link Detection (UDLD) and aggressive UDLD 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:
Up to 128 spanning-tree instances supported
Per-VLAN spanning-tree plus (PVST+) for load balancing across VLANs
Rapid PVST+ for load balancing across VLANs and providing rapid convergence of
spanning-tree instances
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 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 changing root and
designated ports to the forwarding state
Optional spanning-tree features available in PVST+, rapid-PVST+, and MSTP mode:
Port Fast for eliminating the forwarding delay by enabling a port to immediately change from
the blocking state to the forwarding state
BPDU guard for shutting down Port Fast-enabled ports that receive bridge protocol data units
(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
Equal-cost routing for link-level and switch-level redundancy