VLAN overlapping IPs

[wrwiii122]

Ive been taught to use seperate network IPs in different VLANs. Why would this matter if a VLAN is supposed to be a simulated different switch. What would happen if I used the same network on different VLANs?

[thisisshanky]

Traffic from vlan 1 to vlan 2 wont pass without going through a layer 3 device (router). So if you use same subnet on two vlans ,traffic wont pass. When PC 1 in vlan 1 (10.1.1.1) wants to send traffic to PC 2 on vlan 2(10.1.1.2), it sends an arp for Pc2, which will never cross from vlan 1 to vlan 2 (unless vlan 1 to vlan 2 connection is bridged).

Also Layer 3 devices such as routers doesnt allow same ip subnet on its own interfaces.

[wrwiii122]

What if it is a 3550 and you are using SVI or ip routing?