Cisco Catalyst 3750-X User Manual

15-15
Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-21521-01
Chapter 15 Configuring VLANs
Configuring VLAN Trunks
Figure 15-2 shows a network of switches that are connected by ISL trunks.
Figure 15-2 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 40, “Configuring EtherChannels and Link-State
Tracking.”
Ethernet trunk interfaces support different trunking modes (see Ta
ble 15-4). You can set an interface as
trunking or nontrunking or to negotiate trunking with the neighboring interface. To autonegotiate
t
runking, 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
Pro
tocol. However, some internetworking devices might forward DTP frames improperly, which could
cause misconfigurations.
To avoid this, you should configure interfaces connected to de
vices 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
VLAN3VLAN1
VLAN1
VLAN2
VLAN3
ISL
trunk
ISL
trunk
ISL
trunk
ISL
trunk
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Cisco Catalyst 3750-X Specifications

General

Switching Capacity	160 Gbps
Stacking Bandwidth	64 Gbps
Max Stacking Units	9
Layer Support	Layer 2 and Layer 3
Form Factor	Rack-mountable
DRAM	256 MB
Flash Memory	64 MB
Model	Cisco Catalyst 3750-X Series
Ports	24 or 48 10/100/1000 Ethernet ports
Uplink Interfaces	4 SFP or 2 SFP+
Features	StackWise Plus, EnergyWise
Image	IP Base or IP Services
Operating Temperature	0 to 40°C
Operating Humidity	10 to 85% noncondensing