Cisco Gigabit Ethernet Switch Module for HP p-Class BladeSystem Software Configuration Guide

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Cisco Gigabit Ethernet Switch Module for HP p-Class BladeSystem Software Configuration Guide
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Chapter 7 Configuring Interface Characteristics
Understanding Interface Types
Trunk Ports
A trunk port carries the traffic of multiple VLANs and by default is a member of all VLANs in the VLAN
database. These trunk port types are supported:
• In an ISL trunk port, all received packets are expected to be encapsulated with an ISL header, and
all transmitted packets are sent with an ISL header. Native (non-tagged) frames received from an
ISL trunk port are dropped.
• 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 traffic 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 (VLAN ID 1
to 4094) 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 9, “Configuring VLANs.”
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 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 and Layer 2 Trunk Failover.”