Port Trunking in Cisco IOS

Port trunking is the process by which ports are designated as common uplink ports to carry traffic from multiple VLANs across the same physical cable. In the following example, we enable trunking on an etherchannel group to carry specific traffic from VLANs 1 through 99. We also assign the channel to a vlan we’ve designated specifically for etherchannels.

Router# configure terminal
Router (config)# interface port-channel 1
Router (config-if)# switchport access vlan 100
Router (config-if)# switchport trunk encapsulation dot1q
Router (config-if)# switchport trunk allowed vlan 1-99
Router (config-if)# switchport mode trunk
Router (config-if)# ^Z

This configuration will carry traffic for vlans 1-99 across channel group 1. Setting the trunk encapsualtion type is only available on switches that support multiple encapsualtion types. Ensure that spanning-tree is on in order to prevent loops.

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