SVIs

[alsayed]

Hi1

what is the difference between normal creation of vlans<e.g vlan 10 name sales? & the SVIs Interface;is SVI's do ROUTING Between vlans without Vlans creation First

10xs

[m.matteson]

an SVI is a switched virtual interface that allows you to route between vlans internal to the switch that the vlan was created on without having to go to another layer 3 device for routing. i.e sub-interfaces on a router.

[Amit Singh · Accepted solution]

Hi Ali,

SVI is a layer 3 logical interface that you create on the VLAN to enable routing for the vlan or Managing the vlan.If you dont create an SVI on a lyer3 capable device, it will be only a pure layer2 vlan and you will need an external router/routing device to do the inter-vlan routing for you.

When you have a Layer 3 device, you can directly create logical Layer3 interfaces on it i.e SVI to enable routing for the vlans.Depending on the switch you are using, you might have to enable "IP routing" on the switch to enable inter-vlan routing among the vlans.

conf t

ip routing

HTH,

-amit singh

[Jon Marshall · Accepted solution]

Hi Ali

As Michael said an SVI is the layer 3 routed interface for a layer 2 vlan. It does not have to be on the same switch as the vlan was created on although more often than not they are. The layer 2 vlan can exist across many layer 2 switches but you only have one SVI for that vlan (or 2 + HSRP etc.)

You should create the layer 2 vlan first before you create the SVI.

HTH

Jon

[alsayed]

Hi Amit!

Hi Jon!

10XS for all ur replys!

regards

ALI

[hostmaster]

Besides creating the SVI (int vlan <#>) for L3 routing and defining an IP address, are there any other benefits on creating an SVI that will *not* have an ip address assigned such as being able to do a "sh int vl#" to get some vlan stats? On my aggregation switches which are mostly running L3, I have a few L2 only VLANs; my thinking is that MRTG may need to have L2 SVI's created so I can poll. I don't believe there is any hard requirement to create the SVI otherwise.