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Beginner

VTP Use Of Native VLAN

Hi 

In The Topology Shown, Both PCs Are In VLAN1, The Link Between The Switches Is Configured As Trunk Allowing Only VLANs 10-100, & SW1 Is a VTP Server, SW2 Is a VTP Client.

The Two PCs Can't Ping Each Other (Obviously Because The VLAN1 Is Not Allowed On The Trunk).

My Question Is, Why Does VTP Works Fine Even Though The Native VLAN Is Not Allowed On The Trunk?

q.PNG

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VIP Advisor

Re: VTP Use Of Native VLAN

That is default behaviour by design.

 

On the Catalyst enterprise LAN switches, VLAN 1 is enabled by default to allow control protocols to transmit and receive packets across the network topology. However, when VLAN 1 is enabled on trunk links in a large complex network topology, the impact of broadcast storms increases. Because spanning tree applies to the entire network topology, the possibility of spanning tree loops also increases when VLAN 1 is enabled on all trunk links. To prevent this situation, you can disable VLAN 1 on trunk interfaces.

 

When you disable VLAN 1 on a trunk interface, no user traffic is transmitted or received across that trunk interface, but the supervisor engine will continue to transmit and receive packets from control protocols such as Cisco Discovery Protocol (CDP), VLAN Trunking Protocol (VTP), Port Aggregation Protocol (PAgP), Dynamic Trunking Protocol (DTP), and so forth.

 

If you using eve-ng, Right click on device and capture with Wireshark you able to view that information.

 

Hope make sense ?

 

BB
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4 REPLIES 4
VIP Advisor

Re: VTP Use Of Native VLAN

That is default behaviour by design.

 

On the Catalyst enterprise LAN switches, VLAN 1 is enabled by default to allow control protocols to transmit and receive packets across the network topology. However, when VLAN 1 is enabled on trunk links in a large complex network topology, the impact of broadcast storms increases. Because spanning tree applies to the entire network topology, the possibility of spanning tree loops also increases when VLAN 1 is enabled on all trunk links. To prevent this situation, you can disable VLAN 1 on trunk interfaces.

 

When you disable VLAN 1 on a trunk interface, no user traffic is transmitted or received across that trunk interface, but the supervisor engine will continue to transmit and receive packets from control protocols such as Cisco Discovery Protocol (CDP), VLAN Trunking Protocol (VTP), Port Aggregation Protocol (PAgP), Dynamic Trunking Protocol (DTP), and so forth.

 

If you using eve-ng, Right click on device and capture with Wireshark you able to view that information.

 

Hope make sense ?

 

BB
*** Rate All Helpful Responses ***

View solution in original post

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Beginner

Re: VTP Use Of Native VLAN

Thank You Very Much

VIP Advisor

Re: VTP Use Of Native VLAN

a contentious subject, but my opinion is; stay away from using VLAN 1 as part of your LAN. dont default

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Advocate

Re: VTP Use Of Native VLAN

Hi @Ali Hazim ,

 

Check this link:

 

https://learningnetwork.cisco.com/thread/89006

 

Maybe can help you.

 

Regards

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