3 Replies Latest reply: Oct 9, 2010 1:49 PM by Martin RSS

    Layer 3 Switches


      Hello all, I had a question in regard to  inter vlan routing with a Layer 3 switch. If you are using a 2800 series router with only one physical interface you would have to create sub interfaces (router on a stick) to communicate from vlan to vlan. If you have a 6510 switch with multiple interfaces, would you only need to just configure vlan's and not sub interfaces on each interface? Thanks in advance for any feed back.

        • 1. Re: Layer 3 Switches

          yes, you still need to enable routing between vlans.

          • 2. Re: Layer 3 Switches

            On a 6500, or any layer 3 switch for that matter you have 2 choices as far as routing and routed interfaces.  You could configure an ethernet or fiber port on a switch as a routed port.  This would be like the ethernet port on your 2800 router.


            The other option is creating an SVI interface that represents a routed interface for a particular vlan.  So, lets say I have vlan2 on my layer 3 switch.  I would then want to create a Switched Virtual Interface for that vlan.


            #(config)int vlan2

            #(config-if)ip address


            You now have a virtual interface for vlan 2 with the IP of  Because this interface is directly connected to the switch, it is in the routing table of the layer 3 switch.  Think of the SVI  as a couterpart to a routers sub interface.  They are both virtual interfaces.  One is tied to a physical interface, the other tied to a vlan.


            Also, some layer 3 switches actually come in ip routing mode by default, like a 6500 or a 4500, so you wouldn't need to enable IP routing on those types of switches because it's already on by default.

            • 3. Re: Layer 3 Switches

              Great!! Thank you for  that detailed explanation, really clear up that question that I have been a little embarrassed to ask.