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Dynamic VLANs

Posted in Designing VLANs

 

Introduction

Dynamic VLANs were introduced to grant the flexibility and complexity(!) that Static VLANs did not provide. Dynamic VLANs are quite rare because of their requirements and initial administrative overhead. As such, most administrators and network engineers tend to prefer Static VLANs.


Dynamic VLANs

Dynamic VLANs, as opposed to Static VLANs, do not require the administrator to individually configure each port, but instead, a central server called the VMPS (VLAN Member Policy Server). The VMPS is used to handle the on-the-spot port configuration of every switch participating on the VLAN network.

The VMPS server contains a database of all workstation MAC addresses, along with the associated VLAN the MAC address belongs to. This way, we essentially have a VLAN-to-MAC address mapping:

Static VLANs

Posted in Designing VLANs

 

Introduction

VLANs are usually created by the network administrator, assigning each port of every switch to a VLAN. Depending on the network infrastructure and security policies, the assignment of VLANs can be implemented using two different methods: Static or Dynamic memberships - these two methods are also known as VLAN memberships.

Each of these methods have their advantages and disadvantages and we will be analysing them in great depth to help you decide which would best suite your network.

Depending on the method used to assign the VLAN membership, the switch may require further configuration, but in most cases it's a pretty straight forward process. This page deals with Static VLANs while Dynamic VLANs are covered next.

Comparing Old Flat Networks & VLAN Networks

Posted in Designing VLANs

 

Introduction

Designing and building a network is not a simple job. VLANs are no exception to this rule, in fact they require a more sophisticated approach because of the variety of protocols used to maintain and administer them.

Our aim here is not to tell you how to setup your VLANs and what you should or shouldn't do, this will be covered later on. For now, we would like to show you different physical VLAN layouts to help you recognise the benefits offered when introducing this technology into your network, regardless of its size.

The VLAN Concept - Introduction to VLANs

Posted in VLAN Networks

We hear about them everywhere, vendors around the world are constantly trying to push them into every type of network and as a result, the Local Area Network (LAN) we once knew starts to take a different shape. And yet, for some of us, the concept of what VLANs are and how they work might still be a bit blurry.

To help start clearing things up we will define the VLAN concept not only through words, but through the use of our cool diagrams and at the same time, compare VLANs to our standard flat switched network.

We will start by taking a quick look at a normal switched network, pointing out it's main characteristics and then move on to VLANs.

 

The Traditional Switched Network

Almost every network today has a switch interconnecting all network nodes, providing a fast and reliable way for the nodes to communicate. Switches today are what hubs were a while back - the most common and necessary equipment in our network, and there is certainly no doubt about that.

While switches might be adequate for most type of networks, they prove inadequate for mid to large sized networks where things are not as simple as plugging a switch into the power outlet and hanging a few Pc's from it!

For those of you who have already read our "switches and bridges" section, you will be well aware that switches are layer 2 devices which create a flat network:

vlans-concept-1

The above network diagram illustrates a switch with 3 workstations connected. These workstations are able to communicate with each other and are part of the same broadcast domain, meaning that if one workstation were to send a broadcast, the rest will receive it.

In a small network multiple broadcast might not be too much of a problem, but as the size of the network increases, so will the broadcasts, up to the point where they start to become a big problem, flooding the network with garbage (most of the times!) and consuming valuable bandwidth.

To visually understand the problem, but also the idea of a large flat network, observe the diagram below:

vlans-concept-2

The problem here starts to become evident as we populate the network with more switches and workstations. Since most workstations tend to be loaded with the Windows operating system, this will result in unavoidable broadcasts being sent occasionaly on the network wire - something we certainly want to avoid.

Another major concern is security. In the above network, all users are able to see all devices. In a much larger network containing critical file servers, databases and other confidential information, this would mean that everyone would have network access to these servers and naturally, they would be more susceptible to an attack.

To effectively protect such systems from your network you would need to restrict access at the network level by segmenting the exisiting network or simply placing a firewall in front of each critical system, but the cost and complexity will surely make most administrators think twice about it. Thankfully there is a solution ..... simply keep reading.

 

Introducing VLANs

Welcome to the wonderful world of VLANs!

All the above problems, and a lot more, can be forgotten with the creation of VLANs...well, to some extent at least.

As most of you are already aware, in order to create (and work with) VLANs, you need a layer 2 switch that supports them. A lot of people new to the networking field bring the misconception that it's a matter of simply installing additional software on the clients or switch, in order to "enable" VLANs throughout the network - this is totally incorrect!

Because VLANs involve millions of mathematical calculations, they require special hardware which is built into the switch and your switch must therefore support VLANs at the time of purchase, otherwise you will not be able to create VLANs on it!

Each VLAN created on a switch is a separate network. This means that a separate broadcast domain is created for each VLAN that exists. Network broadcasts, by default, are filtered from all ports on a switch that are not members of the same VLAN and this is why VLANs are very common in today's large network as they help isolate network segments between each other.

Securing Your Home Network

Posted in Firewalls

Introduction

Most people who use computers these days have had to deal with a security issue of some kind – whether they are aware of it or not. Everyone has been infected by one of the many worms or viruses floating around the Internet, or have had someone use your password. Most home computer users are victims of attacks that they have no idea about.

For example, certain programs called ‘spyware' come packaged into seemingly friendly programs you download, this spyware can do any one of a number of things, though most often they send your personal information (such as name and email address) and information about what sites you visit to certain companies.

CCENT/CCNA

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