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Chapter 11
Configuring VLANs
Figure 11-2
You can configure a trunk on a single Ethernet interface or on an EtherChannel bundle. For more
information about EtherChannel, see
Failover."
Ethernet trunk interfaces support different trunking modes (see
trunking or nontrunking or to negotiate trunking with the neighboring interface. To autonegotiate
trunking, the interfaces must be in the same VTP domain.
Trunk negotiation is managed by the Dynamic Trunking Protocol (DTP), which is a Point-to-Point
Protocol. However, some internetworking devices might forward DTP frames improperly, which could
cause misconfigurations.
To avoid this, you should configure interfaces connected to devices that do not support DTP to not
forward DTP frames, that is, to turn off DTP.
If you do not intend to trunk across those links, use the switchport mode access interface
•
configuration command to disable trunking.
To enable trunking to a device that does not support DTP, use the switchport mode trunk and
•
switchport nonegotiate interface configuration commands to cause the interface to become a trunk
but to not generate DTP frames. Use the switchport trunk encapsulation isl or switchport trunk
encapsulation dot1q interface to select the encapsulation type on the trunk port.
You can also specify on DTP interfaces whether the trunk uses ISL or IEEE 802.1Q encapsulation or if
the encapsulation type is autonegotiated. The DTP supports autonegotiation of both ISL and
IEEE 802.1Q trunks.
DTP is not supported on private-VLAN ports or tunnel ports.
Note
OL-8915-03
Blade Switches in an ISL Trunking Environment
ISL
trunk
trunk
Blade
switch
Blade
switch
VLAN1
VLAN2
Catalyst 6500 series
switch
ISL
ISL
trunk
Blade
switch
VLAN3
VLAN2
VLAN1
Chapter 33, "Configuring EtherChannels and Layer 2 Trunk
Cisco Catalyst Blade Switch 3020 for HP Software Configuration Guide
Configuring VLAN Trunks
ISL
trunk
Blade
switch
VLAN3
Table
11-4). You can set an interface as
11-17
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