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Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-08
Chapter 13 Configuring VLANs
Configuring VLAN Trunks
shows a network of switches that are connected by ISL trunks.
Figure 13-2
Switches in an ISL Trunking Environment
You can configure a trunk on a single Ethernet interface or on an EtherChannel bundle. For more
information about EtherChannel, see
Chapter 38, “Configuring EtherChannels and Link-State
Ethernet trunk interfaces support different trunking modes (see
). You can set an interface as
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.
Note
DTP is not supported on private-VLAN ports or tunnel ports.
Catalyst 6500 series
switch
Switch
Switch
Switch
Switch
VLAN2
VLAN3
VLAN1
VLAN1
VLAN2
VLAN3
ISL
trunk
ISL
trunk
ISL
trunk
ISL
trunk
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Содержание Catalyst 3750-E Series
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