#ccna #switch #network
Switches are key building blocks for any network.
It has multiple ports and connects multiple devices, such as computers, laptops, wireless access points, printers, cameras and servers; on the same LAN within a building or campus.
A switch enables connected devices to share information and talk to each other.
It is called layer 2 device because it works on layer 2 of the OSI model and it uses mac address in order to share data from one end to other end.
It learns the physical address of the devices that are connected to it and store the physical address called mac address in its mac table.
Unlike hub switch is an intelligent device
Switches are ASIC based .ASIC stands for application specific integrated circuit. This feature helps the switch to make the switching decisions very quickly.
Every port on a switch is in a different collision domain, i.e a switch is a collision domain separator
All ports on a switch are by default in the same broadcast domain.
A broadcast domain contains all devices that can reach each other at the data link layer (OSI layer 2) by using broadcast.
There are two types of switches
Unmanaged switches
An unmanaged network switch is designed so that you can simply plug them in and they work, no configuration required.
Unmanaged switches are typically for basic connectivity.
You'll often see them used in home networks or wherever a few more ports are needed, such as at your desk, in a lab, or in a conference room.
One of the example of unmanaged switches include cisco 100 series switches.
Managed switches
Managed switches can be configure to custom-fit your network.
Managed switches give you greater security and more features .
With the greater control, and flexibility you can better protect your network and improve the quality of service for those who access the network.
One of the example of managed switches in the data centers are cisco nexus 7k series switches.
Before we go through the differences between L2 and L3 switches let’s understand what is layer 2 and layer 3 switch actually.
A Layer 2 switch works with MAC addresses only and does not care about IP address.
Layer 2 switches basically do switching only, which means they operate using devices’ MAC addresses to redirect the data packets from the source port to the destination port
For inter-vlan communication on layer 2 switch a layer 3 router will be required for the device to communicate.
A Layer 3 switch, or multilayer switch, can do all the job that a Layer 2 switch does.
Additionally, it can do static routing and dynamic routing. That means, a Layer 3 switch has both MAC address table and IP routing table, and handles intra-VLAN communication and packets routing between different VLANs as well.
How Switches Forward Frames and Dynamically Populates a Switch MAC Address Table
Lets take an example of a small network with a pc and laptop connected to a switch
When you first boot up the switch it has something know as CAM table/Mac address table.
Cam table is essentially empty and it is going to include our mac addresses that it is going to learn from the end devices on our network.
Lets say this pc has the mac address 0000.0000.0001 and the laptop has mac address of 0000.0000.0002
Lets say if you want to ping from PCA TO PCB ip address of PC-A is 1.1.1.1 and PC-B is 1.1.1.2
Next to communicate with PC-B the PC-A sends an ARP message
ARP in a nutshell is a communication protocol used to resolve the layer-2 address (i e mac address) associated with layer 3 address (i.e ip address)
The switch receives a frame from PC A on FA0/1
The switch examines the source MAC address and compares it to the MAC address table.
If the address is not in the MAC address table, it associates the source MAC address of PC A with the ingress port (FA0/1) in the MAC address table.
After the switch has recorded the source address information, the switch examines the destination MAC address.If the destination address is not in the MAC table the switch floods the frame to all ports, except the ingress port.The destination device (PC B) replies to the frame with a unicast frame addressed to PC A
The switch enters the source MAC address of PC B and the port number of the ingress port into the address table. The destination address of the frame and its associated egress port is found in the MAC address table
The switch can now forward frames between these source and destination devices without flooding because it has entries in the address table that identify the associated ports Cisco offers some exciting models of switches that can be used depending on the requirement and the network you have