Native VLAN on Cisco 3750x vs Cisco 2960S

[sittisakpromsit]

Hi,

I have a scenario where I connect my Cisco switch 2960s with Cisco router 1941 as photo below

My question is when i connect router with cisco 2960s I config interface Gi1/0/1 as a trunk. everything work fine, I can ping from router to switch(172.16.29.2).

But when I changed to cisco 3750x, i config interface Gi1/0/1 as a trunk, it cannot ping from router to switch(172.16.29.2). But after I add native vlan 30 on interface Gi1/0/1 I can ping from router to switch (172.16.29.2)

Any idea why ? is there any different of native vlan on cisco 2960s and 3750x ?

Thank you for your kind answer

John

[mlund · Accepted solution]

Hi John

It seems for me that the 3750 is doing what it should do, if the router do not have subinterfaces and dot1q, it will send traffic without dot1q tag, and the 3750 will drop these packets because they arrive without a tag. That's why native vlan fixes the problem.

The 2960 should work the same way that 3750 do, so I wonder if there is some differences in the config between the switches.

Can You share the config for gi0/1 on the router and also the switchportconfig for both switches.

Also a "show interface gi1/0/1 switchport" for both switches.

/Mikael