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Recently I have study about VLAN (virtual LAN). Its a common that all end-devices of one VLAN have one unique and same subnet and subnet mask like a separate network. And one VLAN host must use a layer 3 device (router, layer 3 switches) for communicating with another VLAN host, which is called inter-VLAN routing.

For inter-VLAN routing, we can use a multi-layer switch SVI configuration. But I am confused about the SVI configuration.

Is it possible to configure an SVI port for more than one VLAN?

Md. Saiful Islam
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    "_Can we configure one SVI of a multilayer switch for more than one VLAN_" No. An SVI is an interface for a VLAN. "_We know that each separate VLAN has its own subnet and subnet mask._" That is incorrect. A VLAN is a layer-2 broadcast domain, and it has nothing to do with layer-3 addressing. – Ron Maupin Feb 19 '21 at 17:30
  • "We know that each separate VLAN has its own subnet and subnet mask". Actually, I was trying to mean through this line that all end-devices of one VLAN have one unique and same subnet and subnet mask like a separate network. Am I right?? And thank you for your comment. – Md. Saiful Islam Feb 21 '21 at 04:36
  • "_Actually, I was trying to mean through this line that all end-devices of one VLAN have one unique and same subnet and subnet mask like a separate network. Am I right??_" No. In most cases that may be true, but the layer-2 VLAN has nothing to do with the layer-3 addressing, and there are cases where you may use one VLAN for multiple layer-3 networks. They are completely separate network layers that really have nothing to do with each other. – Ron Maupin Feb 21 '21 at 04:46
  • Thank you again for your comment. But I have one question, what's the need of having multiple layer-3 networks for one VLAN or LAN. If one VLAN or LAN has multiple layer-3 networks, then which one will be the Gateway address? – Md. Saiful Islam Feb 21 '21 at 05:07
  • You must remember that IPv4 is not the only layer-3 protocol. There are others, such as IPX, AppleTalk, IPv6, etc., and you can have multiple networks of each all on the same VLAN, which is a layer-2 broadcast domain that knows nothing of layer-3. Each layer-3 network on a VLAN will have its own gateway address configured on a layer-3 routed interface in the broadcast domain, which could be a router port or switch SVI. Layer-3 interfaces are not limited to a single address. – Ron Maupin Feb 21 '21 at 05:12
  • Thank you very much for sharing your knowledge. I must try to research more knowledge about these topics that we discuss so far. – Md. Saiful Islam Feb 21 '21 at 06:22

1 Answers1

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A switch virtual interface (SVI) is a binding of a layer-3 address to a layer-2 instance (VLAN). As a VLAN has no physical representation, that interface is virtual.

Usually, there is a single SVI for a VLAN, used for management or routing (between SVIs or routed interfaces). If required, most devices allow you to bind multiple SVIs to a VLAN for multiple addresses or even subnets.

You cannot bind a single SVI to multiple VLANs since a specific IP address cannot exist in multiple VLANs simultaneously.

Zac67
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