Cisco Catalyst 2950 Software Configuration Manual page 345

Chapter 16 Configuring VLANs
Figure 16-2
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
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.
With GigaStack GBICs, dynamic trunking is only supported when two switches are connected by a
•
single GigaStack GBIC link. If trunking is required when more than two switches in a stack are
connected by GigaStack GBIC links, you must manually configure trunking in this manner:
–
–
–
78-11380-12
Switches in an IEEE 802.1Q Trunking Environment
Trunk
port
Switch
Switch
VLAN1
VLAN2
Manually shut down the GigaStack port by using the shutdown interface configuration
command.
Manually configure trunk mode on the GigaStack port by using the switchport mode trunk
interface configuration command on both GBIC interfaces to cause the interfaces to become
trunks.
Use the no shutdown interface configuration command to bring up the GigaStack port.
Catalyst 6500 series
switch
Trunk Trunk
port port
Switch
VLAN3 VLAN2
VLAN1
Chapter 30, "Configuring EtherChannels."
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
Configuring VLAN Trunks
Trunk
port
Switch
VLAN3
Table 16-4). You can set an interface as
16-15