layer 3 untagged with trunk connectivity

[david_kamal2000@yahoo.com]

Hi,

i have core switch connected to firewall

the interface in core configuration is 

interface Ethernet103/1/24
description PA-VM2 -VSwitch2
switchport
switchport mode trunk
no shutdown

interface Vlan3
no ip redirects
ip address 10.153.16.9/21
description Gateway_Of_Server_Zone
no shutdown

and from fw it is untagged interface L3 with ip 10.153.16.8

is that is possible? how they communicate in the switch port is not layer 3?

[Seb Rupik · Accepted solution]

This would not work as you want. 

On a trunk port (eth103/1/4) the default native VLAN is 1 . Any un-tagged traffic arriving on this swithport will be tagged with VLAN1, therefore it will not reach your VLAN3 SVI.

To fix this either create a sub-interface on the firewall and correctly tag the traffic, or change the the native VLAN config on the switch:

!
int Eth103/1/4
  switchport trunk native vlan 3
!

cheers,

Seb.