Cisco Systems 3560 Manual De Usuario

 shows a network of switches that are connected by ISL trunks. 

You can configure a trunk on a single Ethernet interface or on an EtherChannel bundle. For more 
information about EtherChannel, see 

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.

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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