Categories

A sample text widget

Etiam pulvinar consectetur dolor sed malesuada. Ut convallis euismod dolor nec pretium. Nunc ut tristique massa.

Nam sodales mi vitae dolor ullamcorper et vulputate enim accumsan. Morbi orci magna, tincidunt vitae molestie nec, molestie at mi. Nulla nulla lorem, suscipit in posuere in, interdum non magna.

How are VLANs designed?

VLANs or Virtual local area networks are multiple broadcast domains distinct in nature that have been created by partitioning the single layer 2 network in computer networking.

Design of VLANs

– VLANs are kept in mutual isolation with one another for an effective passing of the data packets between them via routers.
– The number of routers may vary from one to more than one.
– Such a partition can only be achieved on devices such as switches or routers.
– The only thing available on the simpler devices is the port level partitioning.
– The VLANs can also be shared among many devices through the use of dedicated cabling for each of them.
– Whereas in more advanced devices, tagging might be used for the packet marking task.
– This lets transportation of the data within various VLANs through a single trunk.
– VLANs are a great solution for simplifying the network design.
– Using a VLAN, hosts can be grouped together based up on their common requirements.
– This does not depend where the hosts are located.
– The attributes of both LAN and VLAN are same.
– Also, for configuring the VLAN membership, one need not do any relocation of the devices rather a software can be used.
– This concept of VLAN is today employed by a number of enterprise level networks.
– All the interfaces are considered to be in the same broadcast domain by the switch in the absence of a VLAN.
– The physical replication of a VLAN would require a parallel but separate connection of network cables as well as equipment.
– One point to be noted is that the bandwidth is shared by VLANs unlike the physical separate networks.

Designing of a VLAN requires two important things:
1. QoS (quality of service) prioritization
2. Aggregated links

– IEEE 802.1Q is the protocol that is commonly used in the configuration of the VLANs.
– In order to provide multi–vendor VLAN support, this method was introduced by the IEEE committee.
– Explicit tagging is performed by both the IEEE 802. 1Q and ISL.
– An external tagging process is used by the ISL that does not introduce any modification in the existing frame.
– The internal tagging is used by the IEEE 802.1Q that lets it to work up on trunk links as well as the access links.
– The commodity hardware can handle the frames since they are standard Ethernet.
– A given Ethernet can have 4096 VLANs at the maximum as per the IEEE 802.1Q.
– However, by this no limit is imposed up on the number of IP subnets in a network as such.
– This is so because multiple IP subnets exist in a single VLAN.
– With the shortest path bridging, the VLAN limit has been expanded to 16 million.
– For multiplexing VLANs, this is one way involving a high speed backbone.
– In ISL, the header is joined with the frame for transporting the VLAN IDs between the routers and the switches and then both are encapsulated.
– Overhead is also added to the data packet in form of a header of 26 – byte that contains a 10 bit VLAN ID.
– In addition to this, a 4 byte CRC is also added to the frame’s end.
– This is for the checking of the frame.
– The header helps in identifying which frame belongs to which VLAN.
– Only if the packet if forwarded out of a port that has been set as a trunk link, then only the VLAN ID is added.
– In the opposite case i.e., if the port has been set as an access link, no encapsulation is done.
– If the size of the collision domain is reduced in an Ethernet segment, the performance of a VLAN can be improved significantly.

Leave a Reply

You can use these HTML tags

<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>