in vlans begin mls...

when you create a vlan and assign it an ip address you have built a switched virtual interface,  a hardware SVI...


sw3550_01(config)#vlan 69
sw3550_01(config-vlan)#name fun
sw3550_01(config-vlan)#exit
sw3550_01(config)#int vlan 69
sw3550_01(config-if)#ip addr 192.168.69.69 255.255.255.0
sw3550_01(config-if)#no shut
sw3550_01(config-if)#end
sw3550_01#

we have bridged the gap between layer 2 and layer 3 on a single interface, a virtual interface, not simply added switchports as members of a vlan. the two are now one. make the vlan and assign it a layer 3 address.  multi-layer switching...

unlike assigning an ip address to a switchport... fail...



sw3550_01(config)#int fa0/15
sw3550_01(config-if)#ip add 192.168.77.77 255.255.255.0
                                        ^
% Invalid input detected at '^' marker.


sw3550_01#sh int fa0/15

FastEthernet0/15 is down, line protocol is down (notconnect)

  Hardware is Fast Ethernet, address is 000f.8ffe.098f (bia 000f.8ffe.098f)




the svi is born from two steps, the vlan interface and the ip address,  with one goal in mind...

sw3550_01#sh run int vlan 69
Building configuration...

Current configuration : 64 bytes
!
interface Vlan69
 ip address 192.168.69.69 255.255.255.0
end


sw3550_01#sh ip int vlan 69
Vlan69 is up, line protocol is up
  Internet address is 192.168.69.69/24
  Broadcast address is 255.255.255.255


sw3550_01#sh int vlan 69
Vlan69 is up, line protocol is up
  Hardware is EtherSVI, address is 000f.8ffe.0980 (bia 000f.8ffe.0980)
  Internet address is 192.168.69.69/24