Cisco IE 4000, Software Configuration Manual

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Configuring VLANs
VLANs
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Although the switch supports a total of 1005 (normal-range and extended-range) VLANs, the number of routed
ports, SVIs, and other configured features affects the use of the switch hardware. If you try to create an
extended-range VLAN and there are not enough hardware resources available, an error message is generated, and
the extended-range VLAN is rejected.
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.
Ethernet trunk interfaces support different trunking modes (see Table 35 on page 278 ). 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.
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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.
IEEE 802.1Q Configuration Guidelines
The IEEE 802.1Q trunks impose these restrictions on the trunking strategy for a network:
Table 35 Layer 2 Interface Modes
Mode Function
switchport mode access Puts the interface (access port) into permanent nontrunking mode and negotiates to
convert the link into a nontrunk link. The interface becomes a nontrunk interface
regardless of whether or not the neighboring interface is a trunk interface.
switchport mode dynamic auto Makes the interface able to convert the link to a trunk link. The interface becomes a trunk
interface if the neighboring interface is set to
trunk or desirable mode. The default switch
port mode for all Ethernet interfaces is dynamic auto.
switchport mode dynamic
desirable Makes the interface actively attempt to convert the link to a trunk link. The interface
becomes a trunk interface if the neighboring interface is set to
trunk , desirable , or auto
mode.
switchport mode trunk Puts the interface into permanent trunking mode and negotiates to convert the
neighboring link into a trunk link. The interface becomes a trunk interface even if the
neighboring interface is not a trunk interface.
switchport nonegotiate Prevents the interface from generating DTP frames. You can use this command only when
the interface switchport mode is access or trunk. You must manually configure the
neighboring interface as a trunk interface to establish a trunk link.