Config Question

[ray_stone]

Below is a config set on router so please confirm the encaplusation is set wrong here!

interface FastEthernet0/0.1

encapsulation dot1Q 1 native

ip address 10.1.110.2 255.255.255.0

ip helper-address 10.1.3.20

ip helper-address 10.1.1.118

ip flow ingress

no snmp trap link-status

no cdp enable

Below is a config of Switch so please confirm of what VLAN traffic will pass from this port (102 or 4) or else it's wrong config.

interface FastEthernet0/5

description Uplink to WAN router

switchport access vlan 4

switchport trunk encapsulation dot1q

switchport mode access

switchport voice vlan 102

no cdp enable

spanning-tree portfast

[cadet alain]

Hi,

It won't work because when you use subinterface on the router with dot1q then the  switch port must be set to trunk.

Alain.

[ray_stone]

Yes, I was also assuming the same but what the following command indicates which is also using "NATIVE"

encapsulation dot1Q 1 native

Please explain.

[Kishore Chennupati]

Hi ray,

interface FastEthernet0/0.1

encapsulation dot1Q 1 native

ip address 10.1.110.2 255.255.255.0

ip helper-address 10.1.3.20

ip helper-address 10.1.1.118

ip flow ingress

no snmp trap link-status

no cdp enable

A simple definition of a native vlan is a vlan which does not get tagged and sent across the trunk. They are sent untagged across the trunk. The native vlans on both sides of the trunk MUST match otherwise the connectivity wont work. you would constantly get mismatch messages.

From your config below the config on the switch is incorrect. It  should be a trunk port so that the 802.1q is agreed upon and hence they  form a trunk.

So, your switch config should look something like this. If you are going to use a native vlan then you need to include it here. By default, the native vlan in a switch is Vlan 1.

interface FastEthernet0/5

description Uplink to WAN router

switchport mode trunk

switchport trunk encapsulation dot1q

switchport trunk native vlan 100     <<< if you decide to use Vlan 100 as native vlan.and this should match on the router as well.

Hope this helps. Let me know if you want more information

Regards,

kishore

[ray_stone]

Ok. Once i change the Switch config in correct order then how the flow of traffic will be. A machine will send a untagged frame to Switch (lets say machine IP is 10.1.1.1) and a VLAN 100 is configured on Switch 10.1.1.254 which is a gateway of machine.

Once swuitch recieve a frame a packte from switch then it will tag it and send it to router then what will happen?