Chapter 1 Product Overview; Q And Layer 2 Protocol Tunneling; Storm Control; Dhcp Snooping - Cisco 4500M Software Manual

Layer 2 Software Features
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802.1Q and Layer 2 Protocol Tunneling

802.1Q tunneling is a Q-in-Q technique that expands the VLAN space by retagging the tagged packets
that enter the service provider infrastructure. 802.1Q tunneling allows service providers to assign a
VLAN to each customer without losing the original customer VLAN IDs inside the tunnel. All data
traffic that enters the tunnel is encapsulated with the tunnel VLAN ID. Layer 2 Protocol Tunneling is a
similar technique for all Layer 2 control traffic. 802.1Q tunneling and Layer 2 Protocol Tunneling are
supported on Supervisor Engine V only.
For information on configuring 802.1Q tunneling, see
Protocol Tunneling."

Storm Control

Broadcast suppression is used to prevent LANs from being disrupted by a broadcast storm on one or
more switch ports. A LAN broadcast storm occurs when broadcast packets flood the LAN, creating
excessive traffic and degrading network performance. Errors in the protocol-stack implementation or in
the network configuration can cause a broadcast storm. Multicast and broadcast suppression measures
how much broadcast traffic is passing through a port and compares the broadcast traffic with some
configurable threshold value within a specific time interval. If the amount of broadcast traffic reaches
the threshold during this interval, broadcast frames are dropped, and optionally the port is shut down.
For information on configuring broadcast suppression, see
Control."
CDP
The Cisco Discovery Protocol (CDP) is a device-discovery protocol that is both media- and
protocol-independent. CDP is available on all Cisco products, including routers, switches, bridges, and
access servers. Using CDP, a device can advertise its existence to other devices and receive information
about other devices on the same LAN. CDP enables Cisco switches and routers to exchange information,
such as their MAC addresses, IP addresses, and outgoing interfaces. CDP runs over the data-link layer
only, allowing two systems that support different network-layer protocols to learn about each other. Each
device configured for CDP sends periodic messages to a multicast address. Each device advertises at
least one address at which it can receive Simple Network Management Protocol (SNMP) messages.
For information on configuring CDP, see

DHCP Snooping

Dynamic Host Configuration Protocol (DHCP) snooping is a security feature that is a component of a
DHCP server. DHCP snooping provides security by intercepting untrusted DHCP messages and by
building and maintaining a DHCP snooping binding table. An untrusted message is a message that is
received from outside the network or firewall that can cause traffic attacks within your network.
Software Configuration Guide—Release 12.2(25)EW
1-2
UDLD, page 1-5
Unidirectional Ethernet, page 1-5
VLANs, page 1-5
Chapter 19, "Configuring 802.1Q and Layer 2
Chapter 38, "Configuring Port-Based Traffic
Chapter 20, "Understanding and Configuring CDP."
Chapter 1 Product Overview
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