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The Network Address Translation Table

Posted in Network Address Translation - NAT

After that simple and informative introduction to the NAT concept, it's time to find out more about how it works and this is where the NAT table comes in.

 

The NAT Table

The NAT table is the heart of the whole NAT operation, which takes place within the router (or any NAT-enabled device) as packets arrive and leave its interfaces. Each connection from the internal (private) network to the external (public-Internet) network, and vice versa, is tracked and a special table is created to help the router determine what to do with all incoming packets on all of its interfaces; in our example there are two. This table, known as the NAT table, is populated gradually as connections are created across the router and once these connections are closed the entries are deleted, making room for new entries.

The NAT table works differently depending on the NAT mode. This is explained in greater detail on each NAT mode's page. For now, we just need to get the feeling for this table to facilitate understanding of each NAT mode.

The larger the NAT table (which means the more memory it occupies), the more bi-directional connections it can track. This means that a NAT-enabled device with a big NAT table is able to serve more clients on the internal network than other similar devices with smaller NAT tables.

The illustration below shows you a typical table of a NAT-enabled device while internal clients are trying access resources on the Internet:

nat-table-1

Network Address Translation (NAT) Concepts

Posted in Network Address Translation - NAT

Before we dive into the deep waters of NAT, we need to make sure we understand exactly what NAT does. So let me give you the background of NAT, why it's here today and how it works. Even though there are different modes of NAT they are all basically extensions to the original concept.

NAT has become so popular that almost all small routers, firewall software and operating systems support at least one NAT mode. This shows how important it is to understand NAT.

 

The NAT Concept

NOTE: NAT is not only used for networks that connect to the Internet. You can use NAT even between private networks as we will see in the pages to follow, but because most networks use it for their Internet connection, we are focusing on that.

The NAT concept is simple: it allows a single device to act as an Internet gateway for internal LAN clients by translating the clients' internal network IP Addresses into the IP Address on the NAT-enabled gateway device.

In other words, NAT runs on the device that's connected to the Internet and hides the rest of your network from the public, thus making your whole network appear as one device (or computer, if you like) to the rest of the world.

NAT is transparent to your network, meaning all internal network devices are not required to be reconfigured in order to access the Internet. All that's required is to let your network devices know that the NAT device is the default gateway to the Internet.

NAT is secure since it hides your network from the Internet. All communications from your private network are handled by the NAT device, which will ensure all the appropriate translations are performed and provide a flawless connection between your devices and the Internet.

The diagram below illustrates this:

nat-concept-1

VLAN Security - Making the Most of VLANs

Posted in VLAN Networks

vlan-security-1Take a look under the hood of this powerful networking tool so that your agency can reap the benefits of bandwidth, availability and security.

It's easy to see why virtual LANs have become extremely popular on networks of all sizes. In practical terms, multiple VLANs are pretty much the same as having multiple separate physical networks within a single organization — without the headache of managing multiple cable plants and switches.

Because VLANs segment a network, creating multiple broadcast domains, they effectively allow traffic from the broadcast domains to remain isolated while increasing the network's bandwidth, availability and security.

Most managed switches are VLAN-capable, but this doesn't mean that they all perform the job equally well. The market has been flooded by thousands of switches that seem to do the job, but special consideration must be taken before making a purchase.

VTP Pruning

Posted in Virtual Trunk Protocol (Cisco VTP)

 

Introduction

As you would be aware a switched network creates one broadcast domain, similar to that of a VLAN powered network where all nodes belonging to the same VLAN are part of the same broadcast domain, receiving all broadcasts sent on their network.

 

The Broadcast And Unicast Problem In VLAN Networks

What we are about to see is how these broadcasts can actually create problems by flooding the VLAN network with unnecessary traffic, and depending on your network setup, this can prove to be a huge problem. The reason for this is because the trunk links interconecting your network switches will carry these broadcasts to every switch in the network, regardless of which VLAN the broadcast is intended for.

In-Depth Analysis Of VTP

Posted in Virtual Trunk Protocol (Cisco VTP)

The previous article introduced the VTP protocol and we saw how it can be used within a network, to help manage your VLANs and ease the administrative overhead providing a stress-free VLAN environment, automatically updating all the network switches with the latest VLAN information.

This article extends on the above by delving into the VTP protocol itself and analysing it's structure and format in order to gain a better understanding and enhance those troubleshooting skills.

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