Posted by: manilageek | March 22, 2010

Change trunk native VLAN from 1 to 2

SwitchB |—————-trunk—————|SwitchA

Current Trunk Configuration:

SwitchA:

SwitchA#sh int g0/1 trunk

Port        Mode         Encapsulation  Status        Native vlan

Gi0/1       on           802.1q         trunking      1

Port      Vlans allowed on trunk

Gi0/1       1-4094

Port        Vlans allowed and active in management domain

Gi0/1       1-2,10,20,30

Port        Vlans in spanning tree forwarding state and not pruned

Gi0/1       1-2,10,20,30

SwitchB:

SwitchB#sh int g0/1 trun

Port        Mode         Encapsulation  Status        Native vlan

Gi0/1       on           802.1q         trunking      1

Port      Vlans allowed on trunk

Gi0/1       1-4094

Port        Vlans allowed and active in management domain

Gi0/1       1-2,10,20,30

Port        Vlans in spanning tree forwarding state and not pruned

Gi0/1       1-2,10,20,30

Change Native VLAN on SwitchA:

SwitchA:

SwitchA#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

SwitchA(config)#int g0/1

SwitchA(config-if)#switchport trunk native vlan 2

SwitchA(config-if)#

23:32:19: %SPANTREE-2-RECV_PVID_ERR: Received BPDU with inconsistent peer vlan i

d 1 on GigabitEthernet0/1 VLAN2.

23:32:19: %SPANTREE-2-BLOCK_PVID_PEER: Blocking GigabitEthernet0/1 on VLAN0001.

Inconsistent peer vlan.

23:32:19: %SPANTREE-2-BLOCK_PVID_LOCAL: Blocking GigabitEthernet0/1 on VLAN0002.

 Inconsistent local vlan.

SwitchB:

SwitchB#

23:32:58: %SPANTREE-2-RECV_PVID_ERR: Received BPDU with inconsistent peer vlan i

d 2 on GigabitEthernet0/1 VLAN1.

23:32:58: %SPANTREE-2-BLOCK_PVID_PEER: Blocking GigabitEthernet0/1 on VLAN0002.

Inconsistent peer vlan.

23:32:58: %SPANTREE-2-BLOCK_PVID_LOCAL: Blocking GigabitEthernet0/1 on VLAN0001.

 Inconsistent local vlan.

Change Native VLAN on SwitchB:

SwitchA:

23:35:22: %SPANTREE-2-UNBLOCK_CONSIST_PORT: Unblocking GigabitEthernet0/1 on VLA

N0001. Port consistency restored.

23:35:22: %SPANTREE-2-UNBLOCK_CONSIST_PORT: Unblocking GigabitEthernet0/1 on VLA

N0002. Port consistency restored.

SwitchB:

SwitchB#conf t

SwitchB(config)#int g0/1

SwitchB(config-if)#switchport trunk native vlan 2

SwitchB(config-if)#

23:36:01: %SPANTREE-2-UNBLOCK_CONSIST_PORT: Unblocking GigabitEthernet0/1 on VLA

N0002. Port consistency restored.

23:36:01: %SPANTREE-2-UNBLOCK_CONSIST_PORT: Unblocking GigabitEthernet0/1 on VLA

N0001. Port consistency restored.

Final Trunk Status:

SwitchA:

SwitchA#sh int g0/1 trunk

Port        Mode         Encapsulation  Status        Native vlan

Gi0/1       on           802.1q         trunking      2

Port      Vlans allowed on trunk

Gi0/1       1-4094

Port        Vlans allowed and active in management domain

Gi0/1       1-2,10,20,30

Port        Vlans in spanning tree forwarding state and not pruned

Gi0/1       1-2,10,20,30

SwitchB:

SwitchB#sh int g0/1 trunk

Port        Mode         Encapsulation  Status        Native vlan

Gi0/1       on           802.1q         trunking      2

Port      Vlans allowed on trunk

Gi0/1       1-4094

Port        Vlans allowed and active in management domain

Gi0/1       1-2,10,20,30

Port        Vlans in spanning tree forwarding state and not pruned

Gi0/1       1-2,10,20,30

Analysis:

When you change the native end of the trunk’s native VLAN both switch will detect VLAN inconsistency (native VLAN mismatch) and put the interface on blocking state on both VLAN 1 and 2, I think other VLAN will continue forwarding data and will not be affected with the configuration. When you then move forward and configure the other end, then the switches detect that the native VLAN mach and consistent the switch then move and unblock the interface forward traffic.

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