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Good afternoon guys,

I've got a question regarding VLANs and SVIs. First of all, I know some concepts about VLANs, and I've been in the IT field for a while. But this one is a bit confusing for me.

When you want VLANs to be routed, for example, having different VLANs with subnets, you would need SVIs, which you define as your default gateway for your hosts.

So first, we create the appropriate VLANs Next, we create a VLAN Interface, which we assign an IP.

However, my silly question is, if we have let's say two switches, or three, I think it doesn't matter. And say we want to use one VLAN across these three switches for communication. Am I supposed to configure the SVI on every switch with the same IP, or do I have to create a new SVI for every switch?

For example, subnet 192.168.0.0/24 would be VLAN 2 on the first switch containing the SVI 192.168.0.1 on the second switch 192.168.0.2 and the third one 192.168.0.3? Or would it be 192.168.0.1 for all the 3 of them?

The reason I'm asking this is, to be honest, I think you would get duplicate IP's since you have three times the same IP assigned, but I think this is a misconception of me.

I've been doing this for a while, and recently another consultant noticed it and said it wasn't necessary to do this, but nor harmful.

So if anyone could give me some more clear explanation in this scenario to give me a clearer view, that would be awesome.

Many thanks in advance! 😊

Greetings

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  • "When you want VLANS to be routed, for example, having different VLANS with subnets, you would need SVI'S, which you define as your default gateway for your hosts." That is the case for layer-3 switches, but you could route on a router and not need the SVIs on the switches (except one for the management of the switch, but it is not the gateway for the hosts). – Ron Maupin Oct 7 '20 at 14:23
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If you have a VLAN that is trunked between switches, then you have one layer 2 domain across all the switches. Unless you have some special cases, all devices on that VLAN would use the same gateway, which would be one SVI on only one of the switches. All devices on the VLAN will use that one gateway.

One exception to this is the use of a First Hop Redundancy Protocol that provides a backup if the switch with the SVI fails. Different manufacturers have different ways of doing this, and if you're interested, you can read more about it.

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  • Hi Ron, Thanks for the input already! So if I understood correctly, you would always need one SVI per VLAN as a rule of thumb. So all hosts on each switch trunked to that one VLAN would point to the same SVI? However, I assume there is also this exception when you want to manage these switches, right? Let's say you want to ssh from one switch to another switch, then you would need 2 different SVI IPs, to distinct the 2 switches from each other. But I assume you would create a separate management VLAN for that as a best practice, or am I wrong? Thanks for the explanation and time so far. – Sinful16 Oct 20 '20 at 20:48
  • You’re exactly correct! – Ron Trunk Oct 20 '20 at 21:16
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SVI(switch virtual interfàce) creating L3 interface for particular subnet and tagging it with particular vlan . SVIs are configured in layer3 switch to optimize routing between different subnets or networks

As per you requirment when your are having multiple switches in setup . Just configuration SVI in switch deployed in core layer and configure trunk ports between distribution switch or access switch to ensure passing all vlan between core switch and access - switch ..

And further connect computers or servers to access -switches by passing specific vlan on access -port as per requirement.

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