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Why trunk still pass vlan 10 frame without "allowed vlan 10"

satyaz
Level 1
Level 1

Hi, i'm sorry if the question a little bit confusing.

So i'm currently learning about trunk troubleshoot (ccna).

 

In the book (ccna 200-125 official cert guide) said that both ends have to have same allowed trunk configuration.

 

But when i tried in packet tracer, i still can ping from PC1 (Vlan 10, 192.168.1.1) to PC2 (Vlan 10, 192.168.1.2) without trunk allowed vlan 10.

vlan.PNG

 Config on Switch01 :

 

int fa0/2

sw mode trunk

 

I don't config on Switch02 because as you know it's automatically "trunked" from Switch01.

 

Could you pelase explain what happend?

I thought fa0/2 (Switch01) will not pass the vlan 10 frame (ping) because i didn't write "sw trunk allowed vlan 10". 

1 Accepted Solution

Accepted Solutions

Seb Rupik
VIP Alumni
VIP Alumni

Hi there,

If you don't explicitly define the allowed VLANs on a trunk link it will trunk them all.

 

Check the output from the command:

sh int trunk

 

cheers,

Seb.

View solution in original post

4 Replies 4

Seb Rupik
VIP Alumni
VIP Alumni

Hi there,

If you don't explicitly define the allowed VLANs on a trunk link it will trunk them all.

 

Check the output from the command:

sh int trunk

 

cheers,

Seb.

Thx a lot very clear for me!

Hi

By default, all the common VLANs between the switches will cross the Trunk if you have not filtered it. Now if you have filtered one or both ends to avoid the VLAN 10, no communication should happen between the devices over the VLAN 10, otherwise it could be a bug on the PT.

 

 




>> Marcar como útil o contestado, si la respuesta resolvió la duda, esto ayuda a futuras consultas de otros miembros de la comunidad. <<

Thank you very much sir for the enlighment.

I think i will build simple ccna lab at home to avoid bug from PT.

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