Wonderful World of WAN...

WAN....What would we do without it?  Life before WAN was time consuming.  Information did not get shared as quickly or if at all.  The wonderful world of WAN, Wide Area Network.

A Wide Area Network is a network that spans a large geographic area.  WANs connect multiple smaller networks, such as LANs (Local Area Networks) or MANs (Metropolitan Area Networks).  The World Wide Internet is the world's most popular and largest WAN.  WANs are often used as connection of LANs within an organization over larger geographical area.  A router connects LANs to a WAN.  The equipment for WANs are more expensive than LANs. 

LAN:

 

 

 

WAN connects the LANs, from different geographical locations, together in order for them to communicate with one another.

 

 

There are four major types of WAN connections available.  





• Dedicated Leased Line:  This is point-to-point connection between LANs.  It is the most secure connection however the most expensive connectivity.  Point to point connection.
• Circuit-Switched:  Use the phone company as the service provider.  A dedicated circuit path is created between the sender and receiver for the duration of the call.  This is less expensive than a leased line, however is slow connection.  There are two types of circuit-switched connections available: asynchronous and ISDN (Integrated Services Digital Network).
• Packet-Switched:  Allows connection to the providers network.  Devices transport packets by a shared single point-to-point  or point-to-multipoint link across a carrier internetwork.  Packets are transmitted over PVC or SVC.  Since the data travels through a shared link, traffic is affected by other customers but the cost tends to be lower than the same bandwidth used for a dedicated line.  Usually use Frame Relay.
• Cell-Switched:  Similar to packet switching, but uses fixed length cells.  Allows heavy traffic loads to be sent more efficiently.  Data is transported across virtual circuits.  This is best for simultaneous use of voice and data. 

There are many different types of protocols used depending on location, type of WAN, and administrator knowledge. 

• Point-to-Point Protocol (PPP)
• Serial Line Internet Protocol (SLIP)
• High-Level Data Link Control (HDLC)
• Frame Relay (FR)
• X.25

To learn more, this video provides extensive information on WAN protocols and connection technologies.

Why VLANs?

VLANs, or Virtual Local Networks, are logical broadcast domains that span multiple physical LAN segments.  Each VLAN functions as a separate LAN by grouping devices by their logical function or application without regard to their physical location by the users.  VLANs are commonly used when separating networks by their department with an organization.  For example, within a company there may be a Human Resources VLAN, a Finance VLAN, an Administration VLAN.  Devices on a particular VLAN should be contained in the same subnet.  

There are several advantages of a VLAN.  VLANs allow for scalability.  Devices on a particular VLAN are not required to be connected to the same network switch.  Users cannot access hosts in other VLANs even though they may be connected to the same switch.  This provides additional security to the infrastructure.  Another advantage of VLANs is cost.  When additional users are added, it is not necessary to upgrade the network infrastructure.  The existing bandwidth is used more efficiently.  VLANs provide similar functions of subnets, like limit the size of broadcast domains, improve network performance and provides security.  So....you may think, why a VLAN and not just a subnet. 

There are also some other important difference between subnets and VLANs. A VLAN is a Layer 2 Concept (MAC address) and subnet is a Layer 3 Concept (IP address). VLANs allow for the creation of both logical and physical networks. Subnets only allow for logical networks. Since the physical network of subnets is the same for all networks, the overall bandwidth for each subnet is shared and therefore reduced. VLANs are usually easier to manage than subnets because they usually are created by their function rather than location. Within an organization, VLANs are more secure than subnets, however more vulnerable to hackers outside the network. It is best practice to have different VLANs in a network and then have a different subnet for each VLAN.

Here is a topology example of VLAN configuration. 

As you can see from the topology above, each VLAN is contained within the same subnetwork.  VLANs are named for identification and configured to assigned ports.  In order for a VLAN to communicate with a different VLAN, it must pass through the Layer 3 device. 
 

Here is an Introduction to VLANs video you may find helpful.

Subnets....simplified!

The process of subnetting an IP network can seem confusing to do, but understanding the concept and benefits of having subnets is most important.  The devices within a subnet are addressed with a common and significant bit group in their IP address.  The logical division of the IP address, or two-level classful hierarchy, contains two fields, the network-prefix and host-number.  The creation of a subnet, or three-level subnet hierarchy, is the division of the host-number, the subnet-number and host-number.

So what is subnetting and why is it important?  Subnetting is the logical practice of dividing an IP network into two or more smaller networks.  Devices within a particular subnet can communicated with one another by forwarding packets through local switches.  Traffic between different subnetworks are exchanged through the router, using the default gateway and then the router determines which subnet the packets should be passed to reach the destination host.  This provides security for computers within their subnetwork.  Subnets restrict the broadcast domain to that particular subnetwork.  The benefit of doing this is to save bandwidth for the overall system and information is only disceminated to necessary locations.  In addition, the overall network is less likely to be affected by viruses that could shut down the whole system and is contained only in that particular subnet.  When it comes to managing the overall network, subnets allow easier management and policy creation to be established. 

There are many videos on the internet explaining IP network and subnetting.  The process of subnetting can be explained using different approaches, but the concept and benefits are the same.  You should use the process that works best for you.  When trying to understand subnetting you need a good understanding of the overall network addressing and routing.  Here is the approach I found to be most helpful.