Switch virtual interface(SVI) is also VLAN interface or logical interface. To understand the concept, let us take the below topology:
There are two PCs connected to switch. PC-1 is connected to Fa0/8 port and PC-2 is connected to Fa0/9. Both the ports of the switch are in different VLAN as you can see above.
In addition, both PC are on different IP Network. PC-1 is on 44.44.44.0 Network and PC-2 is on 55.55.55.0 Network.
Since both the PCs are on different VLAN (different broadcast domain), they cannot communicate with each other. Even PC-1 cannot ping to a switch because switch does not has IP address. In order to ping or communicate with switch, we need to give switch an IP address i.e. we need to create a logical interface which is also called VLAN interface on each VLAN.
While assigning the IP Address to VLAN, make sure that assigned IP should be of same subnet as that of PC. Below is the procedure to create Logical interface or VLAN Interface or SVI on a switch VLAN.
show vlan brief
This commands show the vlan(s) configured on the switch and tells which all ports of a switch comes under the vlan.
Output:
VLAN Name Status Ports
1 default active Fa0/2, Fa0/3
22 VLAN0022 active Fa0/8
55 VLAN0055 active Fa0/9
This is just sample output to explain the SVI.
int vlan <VLAN-ID>
To configure the VLAN interfaces for the particular VLAN, we need to go to config mode first. For that, run “conf” command.
Once you entered in configuration mode, run the below command:
int vlan 22
This will create an interface for the VLAN 22. Now we have to give the ip address to the interface.
ip add 44.44.44.1 255.255.255.0.
run “exit” to come out of the config for VLAN 22.
Similarly, we can do it for VLAN 55 as well. Run the below commands:
int vlan 55
ip add 55.55.55.1 255.255.255.0
show run
To check whether interface is created and IP address is assigned to VLAN. Run “show run”.
It will have big output. Just check for the below from the output:
==============================================
Interface Vlan 22
Ip address 44.44.44.1 255.255.255.0
Interface Vlan 55
Ip address 55.55.55.1 255.255.255.0
==============================================
After this configuration, PC-1 can ping or communicate with PC-2