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I currently have a business network comprised of older but still fully working Layer 2 managed GigE switches. If I would like to have inter-vlan routing on this network (without having to setup a separate network router) would I have to upgrade all of the managed switches to Layer 3, or does having one (it would be the central/main switch in a star topology network) Layer 3 switch in the network allow for inter-vlan routing without having to purchase all new managed switches throughout the network?

Thanks,

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    What type of device does the company use at the border to connect to your ISP? Is there a reason this device can't perform the routing that you need?
    – D34DM347
    Sep 8, 2015 at 14:11
  • The answer to your question is more complicated than I needed to get into to ask my question and get an answer :) There are multiple boarder gateway hardware devices, some of which do not support inter-vlan routing.
    – Griff.J
    Sep 8, 2015 at 14:33

2 Answers 2

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Yes, you just need one Layer-3 switch to perform the routing, the others can stay as Layer-2.

However, if you wish to have multiple VLANs on a given Layer-2 switch, you should confirm that they support VLAN assignments and tagging.

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  • The current layer 2 switches on the network are configured with multiple VLANs and working just fine. Thank you!
    – Griff.J
    Sep 8, 2015 at 14:30
  • So if I understand this correctly: VLAN tagging is a layer 2 function, and VLAN routing is a Layer 3 function. The Layer 2 switches will "route" through the layer 3 switch that assigns the appropriate VLAN tags (is this right?)
    – IceMage
    Feb 12, 2016 at 20:37
  • Any routing is a layer 3 function; you can do it for physical ports, for VLANs, and for any combination of them: you assign one (or more) IP address(es) to an interface, be it physical or virtual, and then you tell the device to perform routing between those IP addresses; it doesn't really matter if routing happens between VLANs or physical ports. But your switch needs to operate at layer 3 in order to do any routing at all.
    – Massimo
    Feb 12, 2016 at 20:46
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    Yeah, VLAN tagging is a layer 2 function, but routing, of any kind, is layer 3 function. Layer 2 switches don't route, they just keep track out of which ports to forward packets for a particular MAC. A layer 3 switch will take those packets and route them to the next hop, be it VLAN, or another router. Also, there's not actually anything as a layer 2 or layer 3 switch; there are only layer 2 switches that have software which can operate at layer 3.
    – GregL
    Feb 12, 2016 at 20:49
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Your device must be able to support layer 3. If that is the case, you can setup inter-vlan routing by creating layer 3 interface on one of the switch interface.

swA(config)#ip routing (to enable routing if it is disable!)

swA(config-if)#no switchport (making this port as a layer3 port.

After these commands, you can do the same config like a router's interface.

SUMMARY:

sw1(config)#ip routing

sw1(config)#int g1/1

sw1(config-if)#no switchport

sw1(config-if)#ip add 10.10.10.10 255.255.255.0

sw1(config-if)#no sh

sw1(config-if)#end

sw1# wr me
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    What makes you assume the OP will get a cisco IOS based layer 3 swtich?
    – Rex
    Feb 12, 2016 at 20:19
  • Also, he specifically asked about inter-VLAN routing; this is port-based routing. You need to add IP addresses to VLAN interfaces (interface vlan X), not to physical interfaces.
    – Massimo
    Feb 12, 2016 at 20:22

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