Specifications

9-4
Catalyst 2970 Switch Software Configuration Guide
78-15462-03
Chapter 9 Configuring Interface Characteristics
Understanding Interface Types
EtherChannel Port Groups
EtherChannel port groups provide the ability to treat multiple switch ports as one switch port. These port
groups act as a single logical port for high-bandwidth connections between switches or between switches
and servers. An EtherChannel balances the traffic load across the links in the channel. If a link within
the EtherChannel fails, traffic previously carried over the failed link changes to the remaining links. You
can group multiple trunk ports into one logical trunk port or multiple access ports into one logical access
port. Most protocols operate over either single ports or aggregated switch ports and do not recognize the
physical ports within the port group. Exceptions are the DTP, the Cisco Discovery Protocol (CDP), and
the Port Aggregation Protocol (PAgP), which operate only on physical ports.
When you configure an EtherChannel, you create a port-channel logical interface and assign an interface
to the EtherChannel. Use the channel-group interface configuration command to dynamically create the
port-channel logical interface. This command binds the physical and logical ports together. For more
information, see Chapter 28, “Configuring EtherChannels.”
Connecting Interfaces
Devices within a single VLAN can communicate directly through any switch. Ports in different VLANs
cannot exchange data without going through a routing device. In the configuration shown in Figure 9-1,
when Host A in VLAN 20 sends data to Host B in VLAN 30, it must go from Host A to the switch, to
the router, back to the switch, and then to Host B.
Figure 9-1 Connecting VLANs with Layer 2 Switches
Host A
Switch
Cisco router
VLAN 20
Host B
VLAN 30
46647