Difference between SI and SVI

Unanswered Question
Oct 21st, 2009

Can anyone clearly gives the differences between SI and SVI like

1.Where we need to create SI or SVI ?

2.Role of both in L2/L3 devices ?

It would be helpful if you can point to some documents which clarifies these in detail.

Thanks in Advance.



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ohassairi Thu, 10/22/2009 - 01:42

with L2 device, all connected Pcs share the same broadcast domain. that means if one computer generates a broadcast frame, this frame will be received by all Pcs.

withL3 switches you can divide your switch to logical broadcast domains called vlan. each vlan will contain Pcs In one IP subnet.

each vlan in the switch will have any Ip @ that will represent the gateway for PCs in this vlan.

so PCs in different vlans can communicate with each other via these gateways

Jon Marshall Thu, 10/22/2009 - 06:46


That makes more sense.

SVIs are used on L3 switches and are created as the L3 interface for a vlan. Without an SVI members of a vlan can communicate with members of the same vlan but they cannot communicate with devices on any other vlan.

Subinterfaces can be used on L3 switches but generally SVIs are the way to go. Subinterfaces are far more common on routers. Again they can be used to route between networks and a common use for them is routing on a stick ie. you have multiple vlans on a L2 switch and you connect this to a router and then configure a subinterface per vlan. This is the equivalent of configuring an SVI for each vlan on a switch.

But subinterfaces are not just used for ethernet - they are often used oon serial interfaces for things like Frame Relay as well.


kovacsteven Thu, 10/22/2009 - 08:14

Dear Bala,

You can use SVI's on L3 switches as Jon posted before but you can also use it on integrated switching modules for routers.

On the attached link you'll find a nice Table wich lists the Cisco IOS Software features supported by SVI and summarized the typical use of these features.



Steven K.


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