From the above diagram it is very clear that hosts which are part of Vlan 10 on swith-1 can easily communicate with the vlan 10 hosts which are part of the switch-1 . We dont require any L3 functionality to be in place for communicating across them since they are part of the same VLAN . But how should hosts which are part of VLAN 10 on switch-1 can communicate with VLAN10 devices in switch 2 ???
But do we really require such facility - if yes why ??
Consider a scenario where we have got our library premises in one vlan ( vlan 10 ) in network segment 1 and computer lab in another vlan (vlan 20) in network segment 2 . We are placed in network segment 2 trying to access computer lab (vlan 20) . Here we can access the library without any issue since both of them reside in the same VLAN & belongs to same network . but wht about the computer lab ?
Exactly for this reason - we need to have a router in between which can route the packets among the VLAN
But do we really require a router for this ? since we will be losing other advantages of what a router can do for us if we simply use this for the routing the vlan packets !!!
We can achieve the same by using an L3 switch -
What is an L3 switch :
A Layer 3 switch is a high-performance device for network routing. Layer 3 switches actually differ very little from routers. A Layer 3 switch can support the same routing protocols as network routers do. Both inspect incoming packets and make dynamic routing decisions based on the source and destination addresses inside
The key difference between Layer 3 switches and routers lies in the hardware technology used to build the unit. The hardware inside a Layer 3 switch merges that of traditional switches and routers, replacing some of a router's software logic with hardware to offer better performance in some situations.
Layer 3 switches often cost less than traditional routers. Designed for use within local networks, a Layer 3 switch will typically not possess the WAN ports and wide area network features a traditional router will always have.
So how do we aheive inter vlan Routing with an L3 Switch ?
- Configure the switch as trunk port ( access port with a default vlan should also be fine ) to receive vlan X on the L3 switch on the interface on which we are intended to receive .
- Assign ip address for those interfaces ( Which are connected to each n/w) .
- You are done :-)
