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Cisco IE 2000 Switch Software Configuration Guide
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Chapter 15 Configuring Interface Characteristics
Information About Configuring Interface Characteristics
Trunk Ports
A trunk port carries the traffic of multiple VLANs and by default is a member of all VLANs in the VLAN
database.
The switch supports only IEEE 802.1Q trunk ports. An IEEE 802.1Q trunk port supports simultaneous
tagged and untagged traffic. An IEEE 802.1Q trunk port is assigned a default port VLAN ID (PVID),
and all untagged traffic travels on the port default PVID. All untagged traffic and tagged traffic with a
NULL VLAN ID are assumed to belong to the port default PVID. A packet with a VLAN ID equal to
the outgoing port default PVID is sent untagged. All other tra ffic is sent with a VLAN tag.
Although by default, a trunk port is a member of every VLAN known to the VTP, you can limit VLAN
membership by configuring an allowed list of VLANs for each trunk port. The list of allowed VLANs
does not affect any other port but the associated trunk port. By default, all possible VLANs (VL AN ID 1
to 4096) are in the allowed list. A trunk port can become a member of a VLAN only if VTP knows of
the VLAN and if the VLAN is in the enabled state. If VTP learns of a new, enabled VLAN and the VLAN
is in the allowed list for a trunk port, the trunk port automatically becomes a member of that VLAN and
traffic is forwarded to and from the trunk port for that VLAN. If VTP learns of a new, enabled VLAN
that is not in the allowed list for a trunk port, the port does not become a member of the VLAN, and no
traffic for the VLAN is forwarded to or from the port.
For more information about trunk ports, see Chapter 17, “Configuring VLANs.”
EtherChannel Port Groups
Note The LAN Base image supports EtherChannel port groups.
EtherChannel port groups 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, group multiple access ports into one logical access port,
group multiple tunnel ports into one logical tunnel port, or group multiple routed ports into one logical
routed 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-channe l 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 phy sical and logical ports together.
For Layer 3 interfaces, you manually create the logical interface by using the interface port-channel
global configuration command. Then you manually assign an interface to the EtherChannel by using the
channel-group interface configuration command.
For more information, see Chapter 40, “Configuring EtherChannels.”
Dual-Purpose Uplink Ports
Some switches support dual-purpose uplink ports. Each uplink port is considered as a single interface
with dual front ends—an RJ-45 connector and a small form-factor pluggable (SFP) module connector.
The dual front ends are not redundant interfaces, and the switch activates only one connector of the pair.