In order for the L3 SVI to show up/up, the VLAN needs to be defined in the VLAN database, there needs to be an active port forwarding for that VLAN in spanning-tree either access or trunk port, and then of course the IP address of your SVI so you can reach the box for management remotely.

show vlan brief ( make sure your vlan is in the vlan db , and your access port is assigned to this vlan if using access port)

show int trunk ( make sure your vlan is allowed on the trunk) should be allowed by default

show spanning-tree vlan 10 (make sure you have an active forwarding port in that VLAN)

-Erik

1.The VLAN defined in the VLAN database (vlan.dat , flash)

2.the trunk conigured:

switchport trunk encapsulation dot1q

switchport mode trunk

3.I dont use stp.

Hi Reza,

1.thanks.

2.What is the command for the SVI?

"then you need to add this vlan (vlan 10) to your trunk connecting your 2950 to other switches"

3.Do you mean if I have trunk port, I need to add the vlan (switchport trunk allowed vlan 10,-----)?

3.Do you mean if I have trunk port, I need to add the vlan (switchport trunk allowed vlan 10,-----)?

yes, exactly

.2.What is the command for the SVI?

SVI and layer-3 vlan are the same thing

here is the config for SVI or layer-3 interface

interface vlan 10

ip address 10.10.10.1 255.255.255.0

desc mgmt vlan

HTH

3. why I dont need to configure:

switchport trunk encapsulation dot1q

switchport mode trunk

4. If I have one switch , and the I want to creat int vlan (layer 3) without access port, it is possible?

3. why I dont need to configure:

switchport trunk encapsulation dot1q

switchport mode trunk

If you have an uplink port (trunk) then you have to add this vlan to the trunk, but if you just configure the commands above then all vlans are allowed You need to have an active port in the vlan in order for it to come up.

4. If I have one switch , and the I want to creat int vlan (layer 3) without access port, it is possible?

In this case if you only have one switch then you need to configure later-2 and layer-3 vlan and add a physical port as an access port  to this vlan.  Then you can connect your PC to that port and that will bring up the vlan

here is an example

interface GigabitEthernet1/0/10

switchport access vlan 10

switchport mode access

spanning-tree portfast

HTH