02 – L3 Switching 7,450 views

Posted by Mo7sin in CCNP, CCNP Switching (642 - 813) On 16/02/2012 at 10:25 PM

Introduction to Layer 3 Switching

In the previous chapter, you were introduced to the concept of inter-VLAN routing, which is required to enable hosts that belong to different VLANs on the same LAN network to communicate with each other. Implementing inter-VLAN routing introduces several benefits, which include the following:

  • Reduces broadcast domains, increasing network performance and efficiency.
  • Multilayer topologies based upon inter-VLAN routing are much more scalable and implement more efficient mechanisms for accommodating redundant paths in the network than equivalent flat Layer 2 topologies that rely on spanning tree alone.
  • Allows for centralized security access control between each VLAN.
  • Increases manageability by creating smaller “troubleshooting domains,” where the effect of a faulty network interface card (NIC) is isolated to a specific VLAN rather than the entire network.

Of course, all of these features must be provided with a very important caveat—inter-VLAN routing should not affect performance, as users expect high performance from the LAN.

A popular approach to providing the benefits of inter-VLAN routing and also ensuring the performance of the LAN is not degraded has been to implement Layer 3 switches, which are essentially Layer 2 switches with a routing engine that is designed to specifically route traffic between VLANs in a LAN environment. Using Layer 3 switches for inter-VLAN routing as opposed to traditional routers is popular (and recommended) for the following reasons:

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