untagged VLAN on subinterface Cisco 2821

Unanswered Question
Apr 16th, 2012

Hello,

I need to configure a subinterface eg g0/0.1 and g0/0.2 with a untagged VLAN for each subinterface on a Cisco 2821.

My configuration is:

Interface giga 0/0.1

encapsulation dot1q 10

In address 10.0.0.1 255.255.255.0

Interface giga 0/0.2

encapsulation dot1q 20

In address 20.0.0.1 255.255.255.0

With this configuration the IP Address is not reachable from any Clients.

untagged VLAN on subinterface Cisco 2821

It is possible and can you help me for the right configuration?

Thanks

Mirko

I have this problem too.
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Reza Sharifi Mon, 04/16/2012 - 12:17

Hi,

Since you are using one physical interface (gig0/0) with 2 different vlans (10,20) and subnets, than you need to tag them.  If you don't want to tag them, than use one physical interface for one vlan/subnet and another one for the other vlan/subnet.

HTH

dancicioiu Mon, 04/16/2012 - 13:19

Hi ,

I think that is posible to use "native" on the subinterface :

Interface giga 0/0.2

   encapsulation dot1q 20 native

Dan

Richard Burts Mon, 04/16/2012 - 13:23

Dan has provided a good solution for one subnet/VLAN. But if I understand the original post correctly then Mirko wants both of the VLANs untagged. And I do not believe that this is possible. The trunking protocol allows for only a single untagged VLAN on the trunk.

HTH

Rick

glen.grant Mon, 04/16/2012 - 13:51

  Maybe you can elaborate on why you think you need both of these subs untagged, never have seen a reason for something like that .

MirkoLaudel Mon, 04/16/2012 - 23:05

Hello,

I get one Network cable with 2 different Networks.

In both Networks are Clients located.

The idea was to start do splitt the Networks in to the Router with different subinterfaces.

Mirko

dancicioiu Mon, 04/16/2012 - 23:31

If you are not using vlan tagging, you can use secondary on the physical interface

int gi0/0

ip address 10.0.0.1 255.255.255.0

ip address 20.0.0.1 255.255.255.0 secondary

This way you can configure 2 network addresses on the same interface

Regards

Dan

Richard Burts Tue, 04/17/2012 - 09:03

I find the statement by Mirko slight ambiguous. When he says one network cable I am not sure whether that means a simple network with everything in one VLAN or whether he really means literally one cable from a switch to the router (which could conceivably be a trunk). My guess is that Dan is correct that it is multiple subnets within a single VLAN (for which secondary addressing is the solution). But I hope that Mirko will clarify for what what the environment really is.

HTH

Rick

MirkoLaudel Sun, 12/30/2012 - 12:40


Hello,

Yes it is right, I have one cable from a Switch to the router with more than one Network.
I woult Splitt this Networks on the router in different VLAN.

Regards
Mirko

mahmoodmkl Sun, 12/30/2012 - 12:46

Hi

In this case then your are good to go with secondry address.

Thanks

Richard Burts Mon, 12/31/2012 - 08:35

Mirko

We need a little more clarification. You tell us that it is a single cable from a switch with more than one network. We also need to know whether the connection on the switch is configured as an access port (there is only a single VLAN on the connection) or whether the connection of the switch is configured as a trunk (there is more than one VLAN on the connection).

From the previous posts I would assume that the switch connection is an access port with only a single VLAN but we need to know this for sure to be able to give you an accurate answer.

If the switch connection is an access port then the implementation of secondary addressing on the router will give you access to both networks. But it would not allow you to split them into separate VLANs on the router.

HTH

Rick

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