dot1q encapsulation on a Cisco 2960G

Answered Question
May 14th, 2007

a project leader bought a dell switch for his rack and I was going to try to uplink it to one of my cisco switches in hopes of configuring trunking on one of the ports and use dot1q to propagate vlan info to the Dell switch. I see on my 3560 switch I'm able to use dot1q encapsulation, but can't seem to find the command on the 2960. Does the 2960 support dot1q? Is that what I'm missing here, is that why the vlans are not being propagated to the dell switch? I have both ports on either end of uplink configured as trunk ports, vlan 1 is passing fine, just no others. Tested connectivity to vlan 1 and it is working.

thank you,

Bill

I have this problem too.
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Correct Answer by mohammedmahmoud about 9 years 8 months ago

Hi,

You have to configure the VLANs on both switches they won't appear automatically.

HTH, please do rate all helpful replies,

Mohammed Mahmoud.

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Overall Rating: 4.8 (4 ratings)
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chris.lepa Mon, 05/14/2007 - 11:14

I'm not all too sure, but I think there may be interoperability issues when using dot1q between a cisco switch and another manufacturer. Try ISL encapsulation instead.

-Chris

mohammedmahmoud Mon, 05/14/2007 - 11:24

Hi,

dot1q is supported on the Cisco 2960, and its a standard (while ISL is Cisco proprietary that runs only on Cisco devices).

Use this commands under the interface:

switchport mode trunk (by default dot1q)

Make sure the native VLAN for an IEEE 802.1Q trunk is the same on both ends of the trunk link. If the native VLAN on one end of the trunk is different from the native VLAN on the other end, spanning-tree loops might result.

HTH, please do rate all helpful replies,

Mohammed Mahmoud.

WILLIAM STEGMAN Mon, 05/14/2007 - 11:38

ok, i have that configured on the cisco

interface GigabitEthernet0/48

description Trunk to Dell

switchport mode trunk

but the output of the vlans is still only showing vlan 1.

chris.lepa Mon, 05/14/2007 - 11:50

Hmm... In the original post, you said that you have a problem finding the dot1q command. The switch you are configuring should support this... Are you sure that you are typing:

(config-if)#switchport trunk encapsulation dotq

?

I used to get messed up all the time trying to type "switchport encapsulation dot1q" without the word "trunk" in there.

If that doesn't work than it's something to do with VTP. You should verify that the VTP domains are the same.

-Chris

WILLIAM STEGMAN Mon, 05/14/2007 - 11:55

i can't type switchport trunk encapsulation dot1q on the 2960, only the 3560, there's no encapsulation keyword on the 2960, so I left it at switchport mode trunk and was hoping the default would kick in and use dot1q.

vtp is an interesting point. the dell doesn't use vtp, must it in order to work with the cisco?

chris.lepa Mon, 05/14/2007 - 11:59

In this case, since it's a Dell, you have to take Mohammed's advice and configure vlans on both switches, then they should be able to communicate.

-Chris

mohammedmahmoud Mon, 05/14/2007 - 12:02

Hi,

The command "switchport trunk encapsulation" is not there because this switch supports only 802.1q and doesn't support ISL, accordingly it doesn't need this command.

HTH, please do rate all helpful replies,

Mohammed Mahmoud.

Correct Answer
mohammedmahmoud Mon, 05/14/2007 - 11:54

Hi,

You have to configure the VLANs on both switches they won't appear automatically.

HTH, please do rate all helpful replies,

Mohammed Mahmoud.

chris.lepa Mon, 05/14/2007 - 11:56

Good point, Mohammed. The switch has to be in VTP client mode if you want it to recieve VLAN information automatically.

mohammedmahmoud Mon, 05/14/2007 - 12:05

Hi Chris,

You are right, one should be a server and the other as a client (or both can be servers), but the problem here is that the Dell switch doesn't support VTP, accordingly VTP can't be used here, and the VLANs must be manually configured on both switches.

HTH,

Mohammed Mahmoud.

chris.lepa Mon, 05/14/2007 - 11:29

Hmm, come to think of it, there are some command variances between cisco switch types. Some cisco switches, you actually have to type:

switchport trunk encapsulation dot1q

While others only support dot1q, so you just type:

switchport mode trunk

Hope that clears up the issue.

-Chris

glen.grant Mon, 05/14/2007 - 13:32

create the layer 2 vlans on both the cisco and dell switches then set up a forced trunk "switchport mode trunk" . Not knowing dells can't tell you how to do that side , read the docs from dell .

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