Layer 2 Switching

Layer 2 switching is the process of using the hardware address of devices on a LAN to segment a network

What Does Switching do…?Switching breaks up large collision domains

into smaller onesCollision domain is a network segment with

two or more devices sharing the same bandwidth

Each port on a switch is actually its own collision domain

Before Layer 2 Switching

First Switched Network

Typical Switched Network Design

Switching ServicesSwitches use ASICApplication Specific Integrated CircuitsLayer 2 Switches are faster then RoutersSwitches create private, dedicated collision

domains and provide independent bandwidth on each port, unlike hubs.

What makes layer 2 switching so efficient..?no modification to the data packet takes

place. The device only reads the frame

encapsulating the packet, which makes the switching process considerably faster and less error-prone than routing processes are.

Bridging vs. LAN Switching Bridges are software based, while switches are hardware based because

they use ASIC chips to help make filtering decisions.

A switch can be viewed as a multiport bridge.

There can be only one spanning-tree instance per bridge, while switches can have many.

Switches have a higher number of ports than most bridges.

Both bridges and switches forward layer 2 broadcasts.

Bridges and switches learn MAC addresses by examining the source address of each

frame received.

Both bridges and switches make forwarding decisions based on layer 2 addresses.

Three Switch Functions at Layer 2

Address learningforward/filter

decisionsloop avoidance

Cisco Switches

Broadcast Storm

Loop AvoidanceRedundant links between switches are a good

idea because they help prevent complete network failures in the event one link stops working.

If no loop avoidance schemes are put in place, the switches will flood broadcasts endlesslythroughout the internetwork. This is sometimes referred to as a broadcast storm.

Multiple Frame Copies

Solution

Spanning Tree Protocol to the Rescue

Layer 3 SwitchA Layer 3 switch works much like a router because it has

the same IP routing table for lookups and it forms a broadcast domain. However, the “switch” part of “Layer 3 switch” is there because:

The layer 3 switch looks like a switch. It has 24+ Ethernet ports and no WAN interfaces.

The layer 3 switch will act like a switch when it is connecting devices that are on the same network.

The layer 3 switch is the same as a switch with the router’s IP routing intelligence built in.

The switch works very quickly to switch or route the packets it is sent.

In other words, the Layer 3 switch is really like a high-speed router without the WAN connectivity.

Why we need it ?

Routing functionality of the Layer 3 switch is there to route between different subnets or VLANs on a campus LAN or any sort of large LAN.

This means that the Layer 3 switch is really for large Ethernet networks that need to subnet into smaller networks. Most of the time, this is done using VLANs.

Cisco Catalyst 3560V2-24TS-S Layer-3 Switch

Today PKR 282367.23

Source: http://www.overstock.com/Electronics/Cisco-Catalyst-3560V2-24TS-S-Layer-3-Switch/4059744/product.html

Vendors

Cisco (http://www.cisco.com/)Juniper (http://www.juniper.net/us/en/)Huawei(http://www.huawei.com/en/)Maipu (http://www.maipu.com/)Foundary

(http://www.brocade.com/index.page)