1. Cisco 3850 Tengige Etherchannel Bug Control

Let’s start by creating a VLAN: SW1(config)# vlan 50SW1(config-vlan)# name ComputersSW1(config-vlan)# exit SW2(config)# vlan 50SW2(config-vlan)# name ComputersSW2(config-vlan)# exitAnd let’s put the interfaces connected to the computers in the correct VLAN: SW1(config)# interface fa0/1SW1(config-if)# switchport access vlan 50 SW2(config)# interface fa0/2SW2(config-if)# switchport access vlan 50The next step is to create a trunk between the two switches. Technically the interfaces between the two switches can also be in access mode right now because I only have a single VLAN. SW1(config)# interface fa0/14SW1(config-if)# switchport mode trunkCommand rejected: An interface whose trunk encapsulation is 'Auto' can not be configured to 'trunk' mode. SW2(config)# interface fa0/14SW2(config-if)# switchport mode trunkCommand rejected: An interface whose trunk encapsulation is 'Auto' can not be configured to 'trunk' mode.I try to change the interface to trunk mode with the switchport mode trunk command. Depending on the switch model you might see the same error as me. If we want to change the interface to trunk mode we need to change the trunk encapsulation type. Let’s see what options we have: SW1(config-if)# switchport trunk encapsulation?dot1q Interface uses only 802.1q trunking encapsulation when trunkingisl Interface uses only ISL trunking encapsulation when trunkingnegotiate Device will negotiate trunking encapsulation with peer on interfaceThis is where you can choose between 802.1Q or ISL encapsulation.

By default our switch will negotiate about the trunk encapsulation type. SW1(config-if)# switchport trunk encapsulation dot1q SW2(config-if)# switchport trunk encapsulation dot1qLet‟s change it to 802.1Q by using the switchport trunk encapsulation command. SW1# show interfaces fa0/14 switchportName: Fa0/14Switchport: EnabledAdministrative Mode: dynamic autoOperational Mode: static accessAdministrative Trunking Encapsulation: dot1q SW2# show interfaces fa0/14 switchportName: Fa0/14Switchport: EnabledAdministrative Mode: dynamic autoOperational Mode: static accessAdministrative Trunking Encapsulation: dot1qAs you can see the trunk encapsulation is now 802.1Q. SW1(config)# interface fa0/14SW1(config-if)# switchport mode trunk SW2(config)# interface fa0/14SW2(config-if)# switchport mode trunkNow I can successfully change the switchport mode to trunk.

Cisco 3850 Tengige Etherchannel Bug Control

SW2# show interface fa0/14 trunkPort Mode Encapsulation Status Native vlanFa0/14 on 802.1q trunking 1Port Vlans allowed on trunkFa0/14 1-4094Port Vlans allowed and active in management domainFa0/14 1,50Port Vlans in spanning tree forwarding state and not prunedFa0/14 50The show interface trunk command is very useful. You can see if an interface is in trunk mode, which trunk encapsulation protocol it is using (802.1Q or ISL) and what the native VLAN is. We can also see that VLAN 1 – 4094 are allowed on this trunk.We can also see that currently only VLAN 1 (native VLAN) and VLAN 50 are active.

Last but not least you can see something which VLANs are in the forwarding state for spanning-tree.I want to show you one more thing about access and trunk interfaces. SW2(config-if)# switchport mode dynamic?auto Set trunking mode dynamic negotiation parameter to AUTOdesirable Set trunking mode dynamic negotiation parameter to DESIRABLEWe can choose between dynamic auto and dynamic desirable.

Our switch will automatically find out if the interface should become an access or trunk port. So what’s the difference between dynamic auto and dynamic desirable? Let’s find out!I’m going to play with the switchport mode on SW1 and SW2 and we’ll see what the result will be. Hi RenePlease can you advise what I can do, I am trying to create vlan 50 on this switch and keep getting following SW1(config)#vlan 50VTP VLAN configuration not allowed when device is not the primary server for vlan database.SW1#sh vtp statusVTP Version: 3 (capable)VTP version running: 3VTP Domain Name: CCIE-domainVTP Pruning Mode: Disabled (Operationally Disabled)VTP Traps Generation: DisabledDevice ID: aabb.cc00.0700Feature VLAN:-VTP Operating Mode: ServerNumber of existing VLANs: 8Number of existing e.