Cisco Dynamic Trunking Protocol Modes Dtp

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Configuring L2 Dynamic Switch Port Details: Dynamic mode on Switch port uses DTP (Dynamic Trunking Protocol) to from trunk port after negotiation. DTP uses two different dynamic mode to make a switch port trunk.

--- Dynamic Desirable --- Dynamic Auto Dynamic Desirable mode can start the DTP negotiation and Dynamic auto mode can listen or reply to negotiation. Combination of using both the mode on a switch to switch link.

---- One side Dynamic Desirable and another side dynamic auto = The link will become Trunk.

---- One side Dynamic auto and another side dynamic auto = The link will become Access port.

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--- One Side Dynamic Desirable and another side dynamic desirable = The link will become Trunk.

--- Configure all inter switch link on sw2, sw3 and sw4 to be in dynamic auto state.

--- Configure all inter switch link on sw1 to be dynamic desirable state. “Configure & Explanation Switch Port Dynamic�

SW-2 SW-2(config)#Interface fastEthernet 0/1 SW-2(config-if)#switchport mode dynamic auto SW-2(config)#interface fastethernet0/2 SW-2(config-if)#switchport mode dynamic auto SW-3 SW-3(config)#interface fastEthernet 0/1 SW-3(config-if)#switchport mode dynamic auto SW-3(config)#interface fastethernet 0/2 SW-3(config-if)#switchport mode dynamic auto SW-4 SW-4(config)#interface fastethernet 0/1 SW-4(config-if)#switchport mode dynamic auto SW-4(config)#interface fastethernet 0/2 2/7

SW-4(config-if)#switchport mode dynamic auto SW-1 SW-1(config)#interface fastethernet 0/1 SW-1(config-if)#switchport mode dynamic desirable SW-1(config)#interface fastethernet 0/2 SW-1(config-if)#switchport mode dynamic desirable Bellow output is showing connectivity between sw-1 and sw-3 SW-1# Show interface fastethernet 0/1 switchport Name: Fa0/1 Switchport: Enabled Administrative Mode: dynamic desirable Operation mode: trunk Administrative trunking encapsulation: dot1q <<port has become trunk port>> Operation trunking encapsulation: dot1q << using encapsulation 802.1q/dot1q>> Negotiation of trunking: on Access mode VLAN: 1 (default) Trunking Native mode VLAN: 1 (default) Voice VLAN: none Administrative private-VLAN host-association: none Administrative private-VLAN mapping: none Administrative private-VLAN trunk native VLAN: none Administrative private-VLAN trunk encapsulation: dot1q Administrative private-VLAN trunk normal VLANs: none Administrative private-VLAN trunk private VLANs: none Operational private-VLAN: none Trunking VLANs Enabled: All Pruning VLANs Enabled: 2-1001 Capture Mode Disable Capture VLANs Allowed: All Protected: False Application Trust: none SW-3# Show interface fastethernet0/1 switchport Name: Fa0/1 Switchport: Enabled Administrative Mode: dynamic auto 3/7

Operation mode: trunk Administrative trunking encapsulation: dot1q Operation trunking encapsulation: dot1q Negotiation of trunking: off Access mode VLAN: 1 (default) Trunking Native mode VLAN: 1 (default) Voice VLAN: none Administrative private-VLAN host-association: none Administrative private-VLAN mapping: none Administrative private-VLAN trunk native VLAN: none Administrative private-VLAN trunk encapsulation: dot1q Administrative private-VLAN trunk normal VLANs: none Administrative private-VLAN trunk private VLANs: none Operational private-VLAN: none Trunking VLANs Enabled: All Pruning VLANs Enabled: 2-1001 Capture Mode Disable Capture VLANs Allowed: All Protected: False Application Trust: none “Dynamic Switchport” on sw1 fa0/1 is configured with dynamic desirable and on sw3 fa0/1 is configured with dynamic auto. As sw1 is configured with dynamic desirable so that sw1 fa0/1 can initiate the DTP the DTP negation and sw3 fa0/1 is configured with dynamic auto so that it can listen to the DTP negotiation. “Configuring L2 dynamic Switchport” As result connection between sw1 and sw3 become trunk. Also sw1 fa0/2 connected to sw2 fa0/2 on sw1 fa0/2 is configured with dynamic desirable and sw2 fa0/2 is configured with dynamic auto. The result become same, which trunk.

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SW1-#Show interface trunk Port Fa0/1 Fa0/2

Mode desirable desirable

Encapsulation n-802.1q n-802.1q

Status trunking trunking

Native Vlan 1 1

Port Fa0/1 Fa0/2

vlans allowed on trunk 1-1005 1-1005

Port Fa0/1 Fa0/2

Vlan allowed and active in management domain 1 1

Port Fa0/1 Fa0/2

Vlans in Spanning tree forwarding state and not pruned 1 none

SW3-#Show interface trunk Port Fa0/1

Mode auto

Encapsulation n-802.1q

Port

vlans allowed on trunk

Status trunking

Native Vlan 1

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Fa0/1

1-1005

Port Fa0/1

Vlan allowed and active in management domain 1

Port Fa0/1

Vlans in Spanning tree forwarding state and not pruned 1

Note: - On the above output “n-802.1q”, here “n” means DTP negotiated.

“Layer 2 Dynamic Switchport” Sw3 fa0/2 is connected to sw4 fa0/2 and both are configured with dynamic auto, as we know none on them can initiate the DTP negotiation, as result both the port has become static access port.

SW-3# Show interface fastethernet0/2 switchport Name: Fa0/2 Switchport: Enabled Administrative Mode: dynamic auto <<The port is configured on this mode>> Operation mode: static access <<The port is running on this mode>> Administrative trunking encapsulation: dot1q Operation trunking encapsulation: dot1q Negotiation of trunking: off Access mode VLAN: 1 (default) Trunking Native mode VLAN: 1 (default) Voice VLAN: none Administrative private-VLAN host-association: none Administrative private-VLAN mapping: none Administrative private-VLAN trunk native VLAN: none Administrative private-VLAN trunk encapsulation: dot1q Administrative private-VLAN trunk normal VLANs: none Administrative private-VLAN trunk private VLANs: none Operational private-VLAN: none Trunking VLANs Enabled: All Pruning VLANs Enabled: 2-1001 Capture Mode Disable Capture VLANs Allowed: All Protected: False Application Trust: none

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