Network Switches and VLANs – A Review
Hubs, switches, and routers are the most frequently used network devices which lets you connect computers, printers, and other devices to communicate.
A Hub is the simplest device to use. Its job is to forward any thing that comes in one port to all other ports on the hub. Every computer connected to the hub sees the same information on the network that every other computer sees.
A switch learns the physical addresses of sending devices by reading the MAC address and mapping it to the port number through which the packet had arrived. Thus it learns the MAC address of every device connected to it as and when it receives a packet from the corresponding device. It forwards packets (frames, as it is more frequently called) to the destination device by reading the MAC address of the destination, and mapping the MAC port.
A router’s job is to route packets, and the most complicated of the three. This device works at layer-3 of the OSI model. They route packets based on the IP address where as a switch forwards packets basedon the MAC address.
The model simplifies the task of building a reliable and scalable internetwork. The hierarchical model defines the following three layers and the specific functions and responsibilities associated:
a. Core layer: The primary function of a Core Layer switch is to switch traffic as fast as possible and provide connectivity between switched networks.
b. Distribution Layer: It is the communication mechanism between the access layer and core layer of the hierarchical model. The Distribution laer determines how packets access the Core layer, provides filtering and routing, and determine access over the campus backbone. This layer is responsible for routing traffic between VLANs, and Inter VLAN routing.
c. Access Layer: It controls users access to network resources. Layer 3 devices such as router ensure that local server travvic does not move to the wider network and this layer is responsible for Layer 2 services, such as VLAN membership, traffic filtering based on MAC address, etc.
Examples of switches according to hierarchical design::
1900/2900/4000 series switches are examples of Cisco Access layer switches.
5000/5500/6000 series switches are the examples of Cisco Distribution layer switches.
6500/8500 series switches are the examples of Cisco Core layer switches
The switches/routers use network operating systems, and they are usually proprietary to the switch manufacturer. For example, Cisco switches use Cisco IOS (Internetwork Operating System), and Juniper switches use JUNOS network operating system. One need to understand the NOS of respective switches to configure or troubleshoot the switch/router network. Some third party switch network simulators are available that simulate the NOS so that a user may get experienced with design, configuration, and troubleshooting the networks in a virtual environment. One such Switch Network Simulator product is available from CertExams.com, which may be downloaded free.
VLANs and VTP:
One of the most important development in switched network environment is the addition of VLAN (short for Virtual Local Area Network) and VTP (Short for VLAN Trunking Protocol). VLANs basically ensure network segmentation, and security. Traffic meant for one VLAN will not pass through another VLAN, thus ensuring better network availability and security. VTP is used to transport packets on a Trunk port. A router (or any Layer-3 device) is required to route packets from one VLAN to another VLAN.
Spanning Tree Protocol (STP):
Loops may occur when there are two or more paths from a source to destination network. STP ensures the loop free transportation of packets from source to destination. If STP is implemented on a VLAN bases, it is called Per VLAN STP or PVSTP.
Conclusion: Network switches have become an essential part of any wired or wireless LAN. The functions performed by switches include packet forwarding, LAN segmentation, Loop free transmission from source to destination network, and data security.
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