Cisco Catalyst 2960 Series, Configuration Manual

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• Trunk ports can be grouped into EtherChannel port groups, but all trunks in the group must have the
same configuration. When a group is first created, all ports follow the parameters set for the first port
to be added to the group. If you change the configuration of one of these parameters, the switch propagates
the setting that you entered to all ports in the group:
◦ Allowed-VLAN list.
◦ STP port priority for each VLAN.
◦ STP Port Fast setting.
◦ Trunk status:
If one port in a port group ceases to be a trunk, all ports cease to be trunks.
• We recommend that you configure no more than 24 trunk ports in Per VLAN Spanning Tree (PVST)
mode and no more than 40 trunk ports in Multiple Spanning Tree (MST) mode.
• If you try to enable IEEE 802.1x on a trunk port, an error message appears, and IEEE 802.1x is not
enabled. If you try to change the mode of an IEEE 802.1x-enabled port to trunk, the port mode is not
changed.
• A port in dynamic mode can negotiate with its neighbor to become a trunk port. If you try to enable
IEEE 802.1x on a dynamic port, an error message appears, and IEEE 802.1x is not enabled. If you try
to change the mode of an IEEE 802.1x-enabled port to dynamic, the port mode is not changed.
Default Layer 2 Ethernet Interface VLAN Configuration
The following table shows the default Layer 2 Ethernet interface VLAN configuration.
Table 196: Default Layer 2 Ethernet Interface VLAN Configuration
Default Setting Feature
switchport mode dynamic auto
Interface mode
VLANs 1 to 4094 Allowed VLAN range
VLANs 2 to 1001 VLAN range eligible for pruning
VLAN 1 Default VLAN (for access ports)
VLAN 1 Native VLAN (for IEEE 802.1Q trunks)
How to Configure VLAN Trunks
To avoid trunking misconfigurations, 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.
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
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How to Configure VLAN Trunks