Wednesday 27 March 2013

2. VLANs and VLAN Trunking


VLAN


VLAN means Virtual Local Area Network, as you guessed it. Its function is to virtually separate ethernet devices or interfaces to a different segment or broadcast domain. We need VLANs because by separating broadcast domain to a smaller group, it will reduce broadcast traffic to the entire broadcast domain (entire broadcast domain means all devices that are connected to a single switch or hub in the same segment without any layer 3 device). How VLANs reduce broadcast traffic? It's simple. Broadcast sent by a device in one VLAN will only be forwarded to the other devices in the same VLAN. Therefore, devices in other VLANs will not be receiving the broadcast traffic, at the same time reducing switch's resources and loads.


In general, there are 2 types of VLANs. L2 VLAN and L3 VLAN. L means Layer in case you don't know. :P I know you must be wondering what's the differences of both VLANs, yes? Let's start with this. L2 VLAN does not have any IP address, but L3 VLAN owns an IP address and is represented as a subnet. Yes you are right. When it is Layer 3, then of course it can be routed in an IP network using routing protocols, as well as communicating with other VLANs. Please take note that unlike L3 VLAN, L2 VLAN devices cannot talk to each other unless there's a layer 3 device such as router configured as their default gateway.

Private VLANs
Will be updated soon.

VLAN Trunking Protocol (VTP)


Why do we need VTP and what is the benefit of using VTP to our network? Imagine if we have 100 switches and all of the switches needs to have the same VLAN configuration. Isn't that a lot of work for us to configure each 100 switches again and again with the same VLAN configuration? That's when VTP come to save us. If we use VTP, it advertises VLAN configuration information to the neighbouring switches so that VLAN configuration information needs to be made to only one switch, with all other switches in the network learning the VLAN information dynamically. So, we don't need to configure all 100 switches with the same VLAN configurations. Thanks to VTP!

VTP Modes
  1. Server Mode - Originates VTP adv., processes and update its VLAN configs, Forward received VTP adv., Saves VLAN in NVRAM or VLAN.dat, can create, modify or delete VLANs.
  2. Client Mode - Same as Server Mode but cannot create, modify or delete VLANs.
  3. Transparent Mode - Same as Server Mode but cannot originate VTP adv., and do not process adv. to update its VLAN configs.
To be continued.

-Soulpower
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1 comment:

  1. Syamin4 April 2013 at 08:41

    LOL pis, lets talk bout something more relevant. Wat u juz wrote ws something u can always referred back in books. Fully understand the general theory is a must, really think u shuldnt drag it any further. Lets get real. I think wat u actually need in here is d discussion on the IOS itself, since d foundation of IOS is basically d same wif all other network device OSes vendor. Guess you left switching tech long time ago. r you still be able to list out d command of vlan without using "?" on IOS? Hehe. Lets start wif simple vlan creation n complete removal, vlan communication via trunk, diffrent in intervlan routing using l2 n l3 switch, with all d possible methods, command and how is it possible to communicate with different vendor equip, since non cisco device does not use vtp to propagate vlan. Yes i have the right to criticize you, since we r still on the same level of switching. i do mean on paper. ;) Turn on d machines brader, before it completely fade out. Jot down d command that u did so we can hav healthy discussion in here, freshen up, curik ilmu :P

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