tagged and untagged with same interface

[Machi Ma]

HI,

I have a problem to config the switchport mode.  It is because flowing in the same port have VLAN ID (tagged) but some did not have VLAN ID (untagged).  I don't know what I should config for switchport mode access/trunk  or is it have Hybrid mode there?

Thx!

[Peter Paluch]

Hi Machi,

Can you explain in more detail why you need such design? This is basically an improper design: either all frames in a particular VLAN shall be tagged or all shall be untagged. Your focus should be on "tidying up" the VLANs in your case, not forcing the switch to cope with both tagged and untagged frames belonging to the same VLAN.

Best regards,

Peter

[Thotsaphon Lueangwattanaphong]

Hi Machi,

     We need more information regarding to your question. It depends on what the device/port/mode is connecting to that port.

Toshi

[Machi Ma]

Hi,

My switch is 2960 now.

It is because I have a devices with bind of both server LAN + Managment together with single port.  That means it will owned two IP address.  Say

Server LAN - untagged (no vlan)

Managment port - tagged (vlan)

Thx!

[Peter Paluch]

Machi,

Okay, I see now. At first I thought that you wanted the same VLAN to contain both tagged and untagged frames.

In this case, you should configure your switchport into the 802.1Q trunk mode. This will allow the port to receive and send both tagged and untagged frames. The untagged frames will be only the frames that belong to a so-called native VLAN configured on the port. All other VLANs will have their frames tagged.

The configuration could look as follows:

interface FastEthernet0/10
 switchport trunk encapsulation dot1q ! Necessary only on 3550 and higher Catalysts
 switchport trunk native vlan 100 ! Here I assume that the mgmt VLAN is 100
 switchport mode trunk

Best regards,

Peter

[Machi Ma]

Hello,

Seems it did not support at my 2960 switch

Switch(config-if)#switchport trunk ?
  allowed  Set allowed VLAN characteristics when interface is in trunking mode
  native   Set trunking native characteristics when interface is in trunking mode
  pruning  Set pruning VLAN characteristics when interface is in trunking mode

How can I enable it?

[Mahesh Gohil]

Hello,

Few switches do not support user settable encapsulation and come with default encap.

you can verify this by below command

#sh interfaces Fa1/0/1 capabilities | inc encap
  Trunk encap. type:     802.1Q

If 802.1q is already there then you can type rest of the commands suggested by peter.

Regards

Mahesh

[Peter Paluch]

Machi,

Just as Mahesh explained and I originally indicated, the switchport trunk encapsulation dot1q command is necessary only for Catalyst switches 3550 and higher (3550, 3560, 3750, ...) that also support a Cisco-proprietary ISL encapsulation on trunks. On 2950 and 2960, only dot1q is supported and therefore the command is not present at all because there is nothing to choose from. Simply proceed with the remaining lines.

Best regards,

Peter