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New Member

Connecting LAN switches together

Hello everyone,

Need some help connecting several Cisco switches together using layer 3 for IP addressing and static routes.

We have several switches in the LAN network with different VLAN's /subnets on all except two that we trunk the VLAN's to each other, this leaves the other six 3560 /3750 switches with no connection and no way to connect the 10.1.1.x network to the 192.168.1.x or other networks on the other switches.

I assume we need to configure all the switches not using the same VLAN's configure the ports for layer 3 that would allow the six switches to connect with each other, and allowing us to use static routes from the one switch to the other that knows nothing of the other networks.

Please let me know the preferred method for connecting the Cisco switches not trunking the VLAN"s but want all networks to talk with each other

Thank you

VIP Super Bronze

Hi,Can you post quick diagram


Can you post quick diagram of your network and point out what vlans need to be on what switch?


New Member

Hello,I'm not trying to bring


I'm not trying to bring any VLAN's from switch to another as the VLAN's are different on some switches, like 3560 have VLAN1 as 192.168.1.x and on the 3750 stack VLAN1 is 10.1.1.x

We need to connect all the 3560 switches to the 3750 Stacks we have as to give them connections to each other, then have the ability to rout any subnet on one switch to the others

3560 TC1 up stairs to the 3750 stack on 1st floor we have two different networks on each switch but need each switch to have the ability to send the traffic to the right switch when needed.

3560 TC1 192.168.1.x subnet users have access to 3750 +5 stack access 10.10.1.x network


Thank you

VIP Super Bronze

Hi,The easiest way to do this


The easiest way to do this is by connecting each 3560 switch to the stack of 3750s via 2 uplinks and have the 3750 stack route traffic between the vlans for you.  This way you keep all the other switches as layer-2 only and create SVIs for each vlan on the 3750s.  In this scenario, there in no need to have connectivity between any of the 3560s, they only connect to the 3750s.


New Member

Ok,can you give me the


can you give me the commands to apply on each switch - like switch one to switch two, I’m sure the commands are different on each switch for doing this.

Do we need an IP address assigned to one port on one of the switches?

Thank you

VIP Super Bronze

ok, if you want to keep all

ok, if you want to keep all the switches as layer-2 then you need to trunk the ports that connect to the layer-3 devices (3750 in this case).

the command to enable trunk is


config t

inter gi0/24


switchport mode trunk

switchport trunk encapsulation dot1q

You need to apply the command on both sides of the link.

the commands for the 3560s and 3750s are the same


New Member

Thank you all for the great

Thank you all for the great input on multiple way for making this work, not looking to do Eather-channels  that requires multiple ports, 

Can you tell me what's the Cisco preferred way for connecting switches together when bringing two or more companies together that allows all networks to communicate together.  Can you provide the commands to use on each Cisco switch for making this work


Thank you   

New Member

No, as to do that you would

No, as to do that you would need to make it a L3 interface.

If using multiple uplinks, you would configure Etherchannel, this is Cisco's form of link aggregation (else one will be disabled via STP)

You would need trunk between the switches, then your core switch would do the routing.

To create an SVI you use the 'int vlan x' command in global configuration mode (where x represents the VLAN number)

For trunking, you type 'switchport mode trunk' on the respective interfaces, DTP may have already negotiated a trunk. So check first by issuing 'sh int trunk'.

For Etherchannel, you really need to do some research.





Cisco Employee

There are a couple of ways

There are a couple of ways you can do this.  One is to configure all of your switches as layer 3.  You'd turn your uplink port to a layer 3 port via the "no switchport" command and assign IPs and static routes.

Another is to use mismatched VLANs.  Unless you're running VTP, which is clearly not the case here, VLANs are local to the switch.  Say S1 is the 3750 stack and S2 is a downstream 3560, and you're using VLAN 1 for two different subnets on each switch.  If S1 1/0/1 is connected to S2 0/1, then you'd do this:

S2 0/1 (VLAN 1)  --->  S1 1/0/1 (VLAN 100)

Connect the two switches together via access ports and put the access ports in different VLANs on the two switches.  Traffic coming from S2 will be placed into VLAN 100 on S1, just as if you had VLAN 100 configured on S2 and were using a trunk to connect the switches.  You then configure your VLAN 100 SVI on S1 with an IP in the correct subnet and enable routing.

This is NOT a recommended way to do things but it will work just fine.  If you have CDP enabled, it will complain about a native vlan mismatch but it won't affect operation.  You can disable CDP on the interfaces to get rid of the warning messages.

I'd recommend that you plan a maintenance window and move to unique vlans on each switch as soon as it's feasible, and use this as a temporary measure.

New Member

What you are referring to re

What you are referring to re the interfaces, is for a L3 design, is that what you are trying to achieve?

The problem at the moment is there are no trunks configured, therefore only one VLAN can traverse between switches.

If these were configured, you would enable routing on your core switch etc, then will make Inter-VLAN connectivity possible.



New Member

Good question,We need all

Good question,

We need all users on the 2nd floor 1st floor on the 192.168.1.x, 192.168.0.x networks to have access to the 10.10.1.x, 10.10.2.x etc. networks on the 3750 stacks, but we can't do this with VLAN's because we have two different VTP domains in place, each switch has a different subnet assigned to VLAN 1, VLAN2 etc. - bring two different companies together to make all networks connect allowing everyone to have access to each network. I was thinking all switches had to have an IP address assigned to one switch and the other switch needs trunking encapsulation dot1q setup, please correct me if I'm wrong - trying to make all this work without taking down the production network.

Please give me help with the commands to use on each switch for connecting them together.

Thank you Sir

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