SVI

Answered Question
Feb 9th, 2010
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Hi,


I believe SVI are virtual router interfaces in layer 3 switches.

My question is

Q1.Are  SVI used to perform intervlan routing on a single switch (SW1)where vlan 10,20,30 exist or can we can use it on connected switch(SW2) also which has the same vlan 10,20,30 ?


Q2.If connected switch has same vlans as SWI1 and intervlan routing is possible do we create different SVI's for the same vlans on SWI2 ?

Correct Answer by Jon Marshall about 7 years 3 months ago

gurkamal01 wrote:


Hi,


I believe SVI are virtual router interfaces in layer 3 switches.

My question is

Q1.Are  SVI used to perform intervlan routing on a single switch (SW1)where vlan 10,20,30 exist or can we can use it on connected switch(SW2) also which has the same vlan 10,20,30 ?


Q2.If connected switch has same vlans as SWI1 and intervlan routing is possible do we create different SVI's for the same vlans on SWI2 ?


There are 2 uses for SVIs.


On a L2 switch you can only have one SVI up/up at any one time. This SVI is not used for user traffic. It is used so you remotely connect to the switch to manage it.


On a L3 switch you can have multiple L3 SVIs and they do route traffic between vlans. So lets say you have -


SW1 -> SW2


where SW1 is L3 and SW2 is L2. You have 3 data vlans 10,20,30.


On SW1 you would create the L3 SVIs for vlans 10,20,30. You would then connect SW2 via a L2 trunk which allows those same vlans. You can then assign ports on SW2 into any of the vlans. A PC connected to a port in vlan 20 for example would have it's default-gateway set to the L3 SVI address of vlan 20 on SW1.


So


Q1 - SVIs can do the inter-vlan routing for multiple switches or more specifically multiple vlans that may exist on many switches.


Q2 - you don't need to. As explained above you can simply connect SW2 with a L2 trunk back to SW1.


Going back to your original problem of the 3750 and core 4 and switch 5 -


if you wanted to route vlan 20 on core 4 you would need to create an SVI. But that might then affect the routing between core 4 and switch 5. The easiest thing to do is to connect core 4 to SW5 with a L2 trunk that allows vlan 20.


Jon

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Ganesh Hariharan Wed, 02/10/2010 - 00:30
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Hi,


I believe SVI are virtual router interfaces in layer 3 switches.

My question is

Q1.Are SVI used to perform intervlan routing on a single switch (SW1)where vlan 10,20,30 exist or can we can use it on connected switch(SW2) also which has the same vlan 10,20,30 ?


Q2.If connected switch has same vlans as SWI1 and intervlan routing is possible do we create different SVI's for the same vlans on SWI2

Hi,


Yes SVI represents a logical Layer 3 interface on a switch and SVI on Cisco Routers is designed to provide basic Layer 3 functions for the Layer 2 switch ports that belong to a specific VLAN. The SVI does not provide the same feature set and functions as the integrated Layer 3 Ethernet ports of the routers and should not be used to entirely replace the Layer 3 Ethernet ports.


SVI are used to perform intervaln routing in switch where u have vlans configured and if you have vlans in different switch then allow the vlan over the trunk to second switch and point a route towards the primary one.


Hope to help !!


Ganesh.H

Correct Answer
Jon Marshall Wed, 02/10/2010 - 00:58
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gurkamal01 wrote:


Hi,


I believe SVI are virtual router interfaces in layer 3 switches.

My question is

Q1.Are  SVI used to perform intervlan routing on a single switch (SW1)where vlan 10,20,30 exist or can we can use it on connected switch(SW2) also which has the same vlan 10,20,30 ?


Q2.If connected switch has same vlans as SWI1 and intervlan routing is possible do we create different SVI's for the same vlans on SWI2 ?


There are 2 uses for SVIs.


On a L2 switch you can only have one SVI up/up at any one time. This SVI is not used for user traffic. It is used so you remotely connect to the switch to manage it.


On a L3 switch you can have multiple L3 SVIs and they do route traffic between vlans. So lets say you have -


SW1 -> SW2


where SW1 is L3 and SW2 is L2. You have 3 data vlans 10,20,30.


On SW1 you would create the L3 SVIs for vlans 10,20,30. You would then connect SW2 via a L2 trunk which allows those same vlans. You can then assign ports on SW2 into any of the vlans. A PC connected to a port in vlan 20 for example would have it's default-gateway set to the L3 SVI address of vlan 20 on SW1.


So


Q1 - SVIs can do the inter-vlan routing for multiple switches or more specifically multiple vlans that may exist on many switches.


Q2 - you don't need to. As explained above you can simply connect SW2 with a L2 trunk back to SW1.


Going back to your original problem of the 3750 and core 4 and switch 5 -


if you wanted to route vlan 20 on core 4 you would need to create an SVI. But that might then affect the routing between core 4 and switch 5. The easiest thing to do is to connect core 4 to SW5 with a L2 trunk that allows vlan 20.


Jon

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