Cisco switches separated by a cloud of non-Cisco IEEE 802.1Q switches. The non-Cisco IEEE 802.1Q
cloud separating the Cisco switches is treated as a single trunk link between the switches.
•
Make sure the native VLAN for an IEEE 802.1Q trunk is the same on both ends of the trunk link. If the
native VLAN on one end of the trunk is different from the native VLAN on the other end, spanning-tree
loops might result.
•
Disabling spanning tree on the native VLAN of an IEEE 802.1Q trunk without disabling spanning tree
on every VLAN in the network can potentially cause spanning-tree loops. We recommend that you leave
spanning tree enabled on the native VLAN of an IEEE 802.1Q trunk or disable spanning tree on every
VLAN in the network. Make sure your network is loop-free before disabling spanning tree.
Information About VLAN Trunks
Trunking Overview
A trunk is a point-to-point link between one or more Ethernet switch interfaces and another networking device
such as a router or a switch. Ethernet trunks carry the traffic of multiple VLANs over a single link, and you
can extend the VLANs across an entire network.
You can configure a trunk on a single Ethernet interface or on an EtherChannel bundle.Note
Trunking Modes
Ethernet trunk interfaces support different trunking modes. 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
(PPP). However, some internetworking devices might forward DTP frames improperly, which could cause
misconfigurations.
Related Topics
Configuring a Trunk Port , on page 2134
Layer 2 Interface Modes, on page 2131
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
2130
Information About VLAN Trunks
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