BCMSN - L3 Switching (Inter-VLAN Routing) [CCNP]

Inter-VLAN Routing: 2 solutions

(1) Router on a stick

(2)Multi-layer Switching using a Layer 3 switch.

(1) Router on a stick

Drawbacks:

-Single point of faiure

-Congestion on link

-Delay of routing (Routers being slower than switches)

(2) Multi-Layer Switching using a Layer 3 Switch

Advantages:

-Routing at wire speed (switching speed)

-Backplane bandwidth (no unnecessary bandwidth usage between switch and router like with 'router on a stick'.

-Redundancy enabled

Disadvantages:

-Cost (Layer 3 switches can start from $5000 as opposed to $300 - $400 for a normal switch.)

Understanding Layer 3 vs. Multilayer Switching:

When the very first packet goes from one VLAN to another VLAN through the layer 3 switch, that first packet is going to go to the router that is inside of the switch (which though from the outside is a switch, is still a router from the inside hence slow transmission, software-based & so on..) but the key here is that once the first packet has hit the router, the router passes it to the switch-side called CEF (the hardware side of the switch) so all future packets fly through there without having to be checked by the router, thus establishing wire speed.

This is what is known as Multilayer switching.

So what is the difference between a Layer 3 switch and a Multilayer switch?

-A layer 3 switch is a switch with a router inside.

-A multilayer switch is a switch that has the ability to cache route information (CEF)

FACT: Every layer 3 switch is also a multilayer switch but not every multilayer switch is a layer 3 switch.

I'll cover more on CEF in a later post...