Switching in network

Switching Services:

1.       Switch use software to create and manage filter table.

2.       Switch use Application Specific Integrated Circuit (ASIC) to build and maintain their filter table.

3.       Layer 2 switches and bridge are faster than routers because they do not take up- time looking at network layer header information.

4.       They look at the frame’s hardware addresses before deciding to either forward, flood or drop the frame.

5.       Switches create private, dedicated collision domains.

6.        Private independent bandwidth on each port.

Layer 2 Switching provide following:

1.       Hardware based bridging

2.       Wire Speed

3.       Low latency

4.       Low cost

Limitations of layer 2 switching:

·         Layer 2 switches not breakup broadcast domain by default – Something that not only limits your network’s size and growth potential, but also can reduce its overall performance.

·         Broadcast and multicasts, along with slow conversion time of spanning tree, there are the big reasons layer 2 switches and bridges cannot replace routers in the internetworks.

Bridging Vs LAN Switching:

                Its true-layer 2 switches really are pretty much just a bridges that give us a lot more ports, but there are some important differences you should always keep in mind.

·         Bridges are software based, while switches are hardware based because they use ASIC chips to help make filtering decision

·         A switch can be viewed as multiport bridge.

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

·         Switches can have higher number of ports than most bridges.

·         Both bridges and switches forward layer 2 broadcasts.

·         Bridges and switches learned MAC addresses by examining the source address of each frame received.

·         Both bridges and switches make forwarding decision based on layer 2 address.

v  Three switch functions at layer 2:

§  There are three distinct functions of layer 2 switching: Address learning, forward or filtering decision, loop avoidance.

v  Address Learning:

§  Layer 2 switches and bridges remember the source hardware address of each frame received on an interface, and they enter this information into a MAC database called forward or filter table.

v  Forward or filter Decision:

§  When frame is received on an interface, the switch looks at the destination hardware address and finds the exit interface at the MAC database. The frame is only forwarded out the specified destination port.  

v  Loop Avoidance:

§  If multiple connections between switches are created for redundancy purpose, network loop can occur. Spanning Tree Protocol (SPT) is used to stop network loops while still permitting redundancy.