Cisco Catalyst 2950 Software Configuration Manual page 323

Chapter 13 Configuring VLANs
Figure 13-2
Figure 13-2 Catalyst 2950, 2900 XL, and 3500 XL Switches in a 802.1Q Trunking Environment
Catalyst
2900 XL
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.
78-11380-04
shows a network of switches that are connected by 802.1Q trunks.
802.1Q 802.1Q
trunk trunk
switch
Catalyst
3500 XL
switch
VLAN1
VLAN2
Catalyst 6000 series
switch
802.1Q
trunk
Catalyst
2950
switch
VLAN3 VLAN2
VLAN1
Chapter 25, "Configuring EtherChannels."
Catalyst 2950 Desktop Switch Software Configuration Guide
Configuring VLAN Trunks
802.1Q
trunk
Catalyst
3500 XL
switch
VLAN3
Table 13-5). You can set an interface as
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