I’ve found that most of the time you can just reboot the router from the web interface and everything will work fine once again. To do this:

Go to the DD-WRT router’s webpage. The default IP address is 192.168.1.1

Click on the “Administration” tab. You will be prompted for the user/password of the router.

Click on “Management” and scroll to the bottom of the page and click “Reboot router”.

Hope this helps you reboot your DD-WRT Router remotely!

Roaming access is actually much easier then you may think. If you are installing additional Access Points (APs) to cover a wider area with Wi-Fi, it is possible to allow clients to roam freely between them. The method that DD-WRT Engineers recommend is to use the same SSID and Security settings on each access point.

Use a different channel on each AP. e.g. if you are in the US and installed two access points, use channels #1 and #11. Or if three access points, then use channels #1, #6, and #11 (setting the channels at least 5 apart should help keep interference between APs to a minimum). If you have a residential gateway with wireless turned on, and just one AP, then the same applies: each gets a different channel.

LAN to LAN uplink

To complete the link between the two routers, connect a LAN port on the central router, to a LAN port on Linksys router (to be used as your WAP). You may need a crossover cable to do this, although many modern routers have an automatic polarity sensing. To test this, connect a standard Ethernet cable between the two routers. If the LAN light comes on, the router has automatically switched the polarity and a crossover cable is not required. *NOTE* – Almost every router you will find will be auto sensing.

When using multiple Access Points, each one should be connected by LAN to LAN uplink as described above. They can even be attached to different switches within the same organization.

I got this information directly from DD-WRT’s website here 

• http://www.dd-wrt.com/wiki/index.php/Linksys_E2000
• http://www.dd-wrt.com/phpBB2/viewtopic.php?t=51486

The reason why I am making this guide is that although the write-up on the previous link is great there are some things that are left out. It kind of assumes that you have  some DD-Wrt experience. My goal with this article is to approach it like you have heard that DD-Wrt is awesome but are now wanting to install it and see what all the fuss is about!

First of all I want to congratulate you on your e2000 router. This router is awesome. It is now the router I recommend for anyone that is looking at new routers. It has Wireless N, Gigabit Network, and it has a wopping 32MB of ram installed on it! Please note that I will be doing the install on a laptop running ubuntu. The steps will be almost identical on Windows and Mac machines. I only mention this just encase you are following along and you are seeing something a tiny bit different.

Overview of the flash process.

There are a couple of things to do when working with this router. I would recommend that you don’t even bother with setting up or configuring the Cisco router. Flashing a router means that we are going to be uploading a single file to the router. The router will process the file and install the software contained in the file to it’s internal memory. NEVER plug in the WAN cable in during setup.

One of the biggest issues with this router is that you need a very specific file for flashing the router. The first time I went to download this file from the DD-WRT website I had a very tough time the link was down. Because of that I have now made my own online copy of the software as I know this file works flawlessly.

Download e2000 DD-WRT flash file - I recommend that you just save the file to your desktop for easy access.

You are going to want to install a telnet client installed on your machine. Putty is a great piece of software for Windows. Linux and Mac machines normally have telnet installed.

Unpack your Cisco e2000.

** This section is for the people that already owned the Cisco e2000 router or went through the setup of it already like changing the password etc. If you haven’t done anything with the router just proceed to the next step called virgin state**

If you have done ANYTHING with the router I recommend reseting everything back to defaults using the 30-30-30 reset. Basically the 30-30-30 reset is where you hold the router in one hand and have it plugged in. Using a pen hold down the reset button for 30 seconds. After the 30 seconds are unplug the power while STILL KEEPING THE RESET BUTTON HELD DOWN! Once that is done re-plug the power back in while STILL KEEPING THE RESET BUTTON HELD DOWN!

Please excuse the caps but most people the first time don’t do this correctly. If at any time you don’t think you’ve done it correctly just restart the process from the beginning.

** Start here if you are sure the router is in a virgin state **

Virgin State

The first thing you want to do is have the router plugged in and your computer plugged into the router with a network cable. DO NOT attempt to do this with a wireless connection. NEVER plug in the WAN cable in during setup. I also recommend that both the computer and router are on a UPS. The reason for this if you happen to experience a power outage while this is happening you will brick the router and I won’t be able to help you.

Open your browser of choice and enter the url (http://192.168.1.1)

Once there you will want to log in. The username will be left *BLANK* and the password is “admin”. Once you log in the router might chirp at you about not using the Cisco setup software. Don’t worry about it. Go to the second last tab on the right. It is called “Administration”. When you click on “Administration” a new line will show up below. It will have a bunch of links. The last one will be called “Firmware Upgrade”. Click the link. You will now be able to browse for the file in the main area and start the flash by clicking “Start to Upgrade”.

The progress bar will go from 0 – 100%. I don’t think the router has ever gone to a DD-WRT page on its own. Once I see that the bar hits 100% I leave for about 5 minutes and then come back to ensure that the flashing is really complete. This is where people might brick the router if they reset the router.

After the 5 minute break I normally just close the Browser window and re-type the 192.168.1.1 address in the URL. Normally you will be presented with the DD-Wrt front page. If this does not happen I recommend that you close the browser and restart the computer you are on. As soon as the computer starts to reboot I unplug the router for 5 seconds. Then plug the router power cable back in. Try to log in to the URL

Now that you are in you will want to click on a tab. This will get DD-WRT to prompt you for the login info.

The default info is: user= “root” and password = “admin”.

Change the username and password. Write this down! The next thing is to secure your wireless connection. By default as soon as you turn on the device the wireless is completely open.

The next thing is to telnet into the DD-WRT box.

To log in you will need to log in with the user “root” and password = “admin” or what ever you changed it in the last step. Please note that the user will ALWAYS be root even if your web interface is something else! I don’t know why this is but it is what it is.

These are the commands that you will need to run at the terminal prompt. Each command must be typed (or copied) exactly. After each command is entered you must hit “enter”. After hitting reboot the router will reboot. It will take just under a minute for a full reboot.

nvram set clkfreq=300,150,75

nvram commit
reboot

Some people have some issues with disconnects with the router. I normally just make these changes while I am setting everything all up.

Wireless > Channel > Ch 161 (5GhZ)

Wireless > Channel > Ch 9 (2.4GhZ)
Wireless > Security > WPA2 Personal - AES
Wireless > Advanced Wireless Settings > Beacon Interval: 75
Wireless > Advanced Wireless Settings > Fragmentation Threshold: 2306
Wireless > Advanced Wireless Settings > RTS Threshold: 2307
Security > Firewall > Block Anonymous WAN Access <--- Uncheck

You are now done! Enjoy an awesome router. Hope you liked this write up.

Click on Link for a larger version of the network Map.

While this might not be the Most complex network out there, this network I will give the user reading the post a good fundamental view on how to start planning a network as well as building it out. Whether it is a house, a renovation, or a building a network. You should always at least have some sort of plan laid out in front of you. If you do make a mistake I guarantee that you will be able to be able to trouble shoot things faster then if you didn’t make a plan.

The network that is laid out above you will give you two separate real world networks. That is, You will have two single networks that will both be connected to an Internet IP address. The reason why I chose to layout my network this way was I wanted to do “REAL WORLD” testing. Using this layout I can actually test a VPN connection inside my own house instead of having to go “Outside” the home network to do the testing.

You might be wondering how I am going to do this. My ISP give out two Dynamic IP address. The first router will actually just be a glorified switch. It will allow Routers 1 and 2 to get their own IP address off the same Internet connection. I am going to be using two fairly fast computers. I am going to make one of the two computers a Virtual server. The other one I will be writing the tutorial from. The Virtual server will have two network cards installed on it. One NIC will be plugged into Router #1 and the other NIC will be plugged into Router #2. Half the Virtual Machines will use a Virtual NIC that using the real NIC #1 and the other half with use a Virtual NIC that uses NIC#2.

We are going to have mail, Web and Files servers each network. I will also have clients in each network.

If this sounds interesting please tune back in a few weeks while I engineer out this network. We will stop and look at security and different ways of doing this along the way. If you bookmark this page I will link to each section as I make them.

1. Connectivity Issues
2. Name Resolution Problems

Connectivity issues are one of the harder issues to troubleshoot especially in a complex network. In this post I will only be covering how to troubleshoot Connectivity issues using some of the built in network tools. At any stage if you get a successful connection just go on to the next item in the list.

1. Make sure you have the correct IP Address of the server
2. I can’t say this enough. CHECK YOUR TCP/IP configuration!! I have seen too many times where someone has entered a STATIC ip address when the address should have been handed out by DHCP or someone entered an invalid Network address. If you aren’t sure then ask the network administrator what the IP Address should be. If you are the network administrator then you should have planned things out a little bit better
3. Sometimes the OS or TCP/IP stack can become corrupted. An easy way to check for this is just to ping 127.0.0.1
4. Ping the local address. This normally looks like “ping 192.168.1.2” or “ping 10.1.1.2” etc
5. Ping items on the local subnet that known to be up and running
6. Clear the ARP cache table
7. Verify the gateway. You can find the gateway by looking at the TCP/IP properties or by doing an “ipconfig" (Windows) or “ifconfig” (Linux/Unix).
8. Trace the route to the remote host
9. Double Check IP of the server

The PID is short for the “Program ID” number and all running apps will have a PID. Why this is important is that if we run the NetStat command we will be able to figure out what network applications are running. This is great for finding things like viruses or for apps that your kid might have installed.

The first thing you will want to do is open a command line by typing “Cmd” and enter in the start menu search box.

type:

This will output a bunch of items on the screen.  The “-a” will show you everything that is listening/running on your machine. The “-o” switch will give you one more column of info. The PID column. This is the part of the newer update.

Here’s an example of something you might not know what it is off the top of head.

Now that the know the PID is equal to “4432” we can go to our task manager and sort the programs by the PID to figure out what application is using our network card!

Open the Windows Task Manager. Click “View” and then “select columns…”

Check “PID” and click “OK”.

Sort the task manager by the “PID” column. You will see that the PID should be running in the task manager. If it isn’t it’s a good sign that the program is no longer running or the Virus has hidden it from the Task manager view.

All legit apps should be shown here. As you can see from my example the port is being used by the “Windows Live Communications Platform”. Again you can go through the list of apps that are running by doing the same thing over and over again. If you like this maybe check out some of my other HOW TO posts.

UPDATE – You can also find out the file that is making the connection by typing: tasklist /fi “PID eq 4432”. Bascially you’re asking the executable “Tasklist” to filter “/fi” based on anything in the list with the “PID” equal (eq) to “4432”. See below for the info. I havne’t been able to view the details through the command prompt.

This post has nothing to do with Apple Mac computers. The Mac Address of a computer is a physical address that is burned into the card at the time of purchase. The MAC address is a layer 2 address and all IP addresses get converted to the MAC address using ARP.

Windows by default (Linux as well) comes with a program called “ARP”. If you run:

“arp /a”

from a command line you will see the MAC address of the computers you are able to talk to on your LOCAL network. If you want to check what the MAC address is you only have to ping the computer. Write down it’s IP address and then run the above ARP command. The ARP command will output the IP address of the computers it has talked to and show you what that computer’s MAC address is.

There are some pretty big programs out there that you have to “pay for” in order to get this functionality. Really those programs are really just doing these two command and reporting back to you.

The most obvious difference between the two protocols is the length of their source and destination addresses. The whole point of making the switch to IPv6 is to compensate for a global shortage of IP addresses. It only makes sense that the IPv6 protocol has a larger address space than the IPv4 protocol does.

The IPv4 protocol uses a 32-bit source and destination address. These addresses are typically represented as a series of four octets. As I’m sure you know, a typical IPv4 address looks something like this: 192.168.0.1.

In contrast, an IPv6 address is 128 bits in length. This allows for a total of 3.4×10³⁸ (or 340,000,000,000,000,000,000,000,000,000,000,000,000)  addresses. There are several different ways of representing an IPv6 address. An IPv6 address is normally written as eight groups of four hexadecimal digits, each separated by colons. For example, an IPv6 address looks like this: 2001:0f68:0000:0000:0000:0000:1986:69af.

You might be looking at the sample address listed above and thinking that typing an IPv6 address involves a lot of effort. Fortunately, IPv6 addresses can be shortened by eliminating zeros. There are two rules that must be followed when condensing an IPv6 address. First, a series of four consecutive zeros can be replaced by two colons, so long as there is only one set of double colons in the resulting address. Using this rule alone, our sample address from above could be condensed to look like this: 2001:0f68::0000:0000:0000:1986:69af

In the example above, we were only able to eliminate one block of zeros because the rule says that there can only be a single set of double colons in an address. Obviously, the sample address above is still a lot to type. Fortunately, the second rule will allow us to make this address a lot shorter. The second rule states that leading zeros in a group can be omitted. What this means is that if a block of four numbers starts with a zero, zero can be removed leaving three numbers in the block. If that three digit block of numbers happens to start with a zero, then the zero can be removed again. The process goes on and on so long as there is a zero in the left-hand position in a block. It’s a little tricky to try to explain the process, so I will demonstrate it below. I will start with our original sample address and then work toward condensing that address.

2001:0f68:0000:0000:0000:0000:1986:69af
2001:f68:000:000:000:000:1986:69af
2001:f68:00:00:00:00:1986:69af
2001:f68:0:0:0:0:1986:69af
2001:f68::1986:69af

Notice that in each line, I simply stripped away the leading zero from each section. Since there were several sections containing all zeros, I was able to completely remove the sections and replace them with a double colon. This was only possible because the sections containing all zeros were found in a row. If the sections of zeros had been scattered, then only one set of zeros could have been completely eliminated (because you are only allowed a single set of double colons). All the other sets of zeros would have to be represented as a single zero.

Using IPv6 Addresses in URLs

Although DNS servers make it possible to access a website by using a fully qualified domain name rather than an IP address, it is still a somewhat standard practice to enter an IP address as a part of a URL. For example, my personal website uses the URL www.brienposey.com, which corresponds to the IP address 24.235.10.4. It would be possible to access my website by entering the following URL: http://24.235.10.4

Most casual Web surfers do not make a habit of entering IP addresses in place of fully qualified domain names. Even so, the practice does exist. This is especially true for private Web applications. Not associating a fully qualified domain name with an application makes it a lot less likely for an unauthorized person to stumble onto the application accidentally.

When an IP address is used in place of a fully qualified domain name, a port number is sometimes specified as part of the address. If you simply enter HTTP:// followed by an address, then your Web browser assumes that you want to use port number 80. However, you can specify any port that you want by appending a colon and the port number to the end of the address. For example, if you wanted to access the www.brienposey.com website by IP address, and specifically require a port 80 to be used, then the command would look like this: http://24.235.10.4:80

The IPv6 protocol can also be used as a part of a URL. If you pay attention to the IPv6 format, you’ll notice that an IPv6 address contains a lot of colons. This poses a bit of a problem since your Web browser typically treats anything after a colon as a port number. That being the case, IPv6 addresses are enclosed in brackets when they are used as a part of a URL. For example, if you were to use our sample IPv6 address in a URL, it would look something like this:

HTTP://[ 2001:0f68:0000:0000:0000:0000:1986:69af]/

Just as you can specify a port number alongside an IPv4 address, you can also specify a port number when using an IPv6 address. The port number follows the exact same format as it does when IPv4 is being used, and falls outside of the brackets. For example, if you were wanting to access the website at our sample IPv6 address over port 80, the URL would look something like this:

HTTP://[ 2001:0f68:0000:0000:0000:0000:1986:69af]:80/

Notice that the port number, in this case 80, falls between the close bracket and the ending slash. A colon is also used to designate the port number, just as it is in the IPv4 protocol.

If you’re familiar with IPv4, then you know that an IPv4 address consists of four different octets of data, each separated by a period. Part of this address is the network number and the remaining bits identify a specific host on the network. The actual number of bits that are dedicated to the network number and to the host number vary depending on the subnet mask.

Just as an IPv4 address is broken into different parts, so is an IPv6 address. In the previous article, you learned that IPv6 addresses are 128 bytes in length. When an IPv6 address is written in its full form, it is expressed as eight different sets of four numbers, each set separated by a colon. Each of these four digit sets represents 16 bits of data. Each of these 16 bit fields has its own specific purpose.

An IPv6 address is broken into three different parts; the site prefix, the subnet ID, and the interface ID. These three components are identified by the position of the bits within the address. The first three fields in an IPv6 address make up the site prefix. The next field represents the subnet ID, and the last four fields are used for the interface ID. 

The site prefix is similar to an IPv4 network number. It is the number that is assigned to your site by an ISP. Typically, all of the computers within a site would share the same site prefix. The site prefix tends to the public in nature since that uniquely identifies your network and allows your network to be accessible from the Internet.

Unlike the site prefix, the subnet ID is private because it is internal to your network. The subnet ID describes the network’s site topology. The subnet ID works very similarly to the way that subnetting works in the IPv4 protocol. The biggest differences are that these subnets can be 16 bytes in length, and is expressed in hexadecimal format rather than in dotted decimal notation. An IPv6 subnet typically corresponds to a single network branch (site) just as an IPv4 subnet does.

The interface ID works similarly to an IPv4 host ID. This number uniquely identifies an individual host on your network. The interface ID (which is sometimes referred to as a token) is typically configured automatically based on the network interface’s MAC address. The interface ID can be manually configured in EUI-64 format.

To see how an IPv6 address is divided into its various subcomponents, take a look at the following address:

2001:0f68:0000:0000:0000:0000:1986:69af

The site prefix portion of this address would be: 2001:0f68:0000. The next field, 0000, represents the subnet ID. The remaining bytes (0000:0000:1986:69af) compose the interface ID.

Typically when a prefix is expressed, it is written in a special format. Zeros are suppressed in the manner explained in the previous article, and the prefixes followed by a slash and another number. The number after the slash indicates the number of bits included in the prefix. In my earlier example, I mentioned that the site prefix for the address 2001:0f68:0000:0000:0000:0000:1986:69af was 2001:0f68:0000. Since this prefix is 48 bits in length, we would add a /48 to the end of it to express it properly. With the zeros suppressed, a prefix looks like this: 2001:f68::/48

Types of IPv6 Addresses

Another thing that is unique about the IPv6 protocol is that there are actually three different types of IPv6 addresses; unicast, multicast, and anycast.

Unicast addresses are used to identify an individual host on a network. Multicast addresses, on the other hand, identify a group of network interfaces that typically reside on multiple computers. When a packet of data is sent to a multicast address, that packet is sent to all network interfaces in the multicast group.

Like multicast addresses, anycast addresses identify a specific group of network interfaces that usually reside on multiple computers. So what makes an anycast route different from a multicast group? When packets are sent to a multicast address, they are sent to all of the network interfaces in the group. In contrast, when packets of data are sent to an anycast address, the packets are not sent to the entire group. Instead, they are only sent to the member that is in the closest physical proximity to the sender.

Unicast Addresses

Earlier, when I showed you the format of an IPv6 address and what the various bit positions were used for, I was showing you an example of a unicast address. There are actually two different types of unicast addresses; global unicast addresses and link local unicast addresses. As the names imply, a global unicast address is globally accessible, while a link local unicast address is accessible only to other computers that share the link. The IP address format that I showed you earlier was that of a global unicast address. I chose to talk about this type of address because it is the most common.

Link local unicast addresses used a different address format from global unicast addresses. Like global unicast addresses, link local unicast addresses are also 128 bytes in length. The difference is that the bytes are distributed differently and the address uses a special site prefix.

In a link local unicast address, a site prefix occupies the first 10 bits of the address rather than the first 48 bits, as is the case with a global unicast address. The site prefix used by a link local unicast address is: fe80.

Since the site prefix space has been shortened (compared with a global unicast address), you may not be surprised to learn that the amount of space allocated to the subnet ID has been extended from 16 bits to 64 bits. What might surprise you is that these 64 bits are not actually used. Keep in mind that a link local IP address is only valid for machines sharing a common link. As such, there is no reason to have a subnet ID. The 64 bits of the address space that are reserved for the subnet ID are therefore expressed as zeros.

The interface ID for a link local unicast address is 54 bits in length. The interface ID is almost always derived from the 48 bit MAC address assigned to the network interface card to which the protocol is bound. Below is an example of a link local unicast address:

Fe80:0000:0000:0000:0000:0000:23a1:b152

Of course when IPv6 addresses are written out they are usually expressed with leading zeros suppressed. Therefore, the more technically correct expression of this address is:

Fe80::23a1:b152

When the addresses expressed are with zeros suppressed, the address might at first look like any other IPv6 address. Remember that you can tell the difference between a link local unicast address and other types of addresses because a link local unicast address will always began with fe80.

When a packet of data is sent to a multicast address, that packet is sent to all network interfaces in the multicast group. Like multicast addresses, anycast addresses identify a specific group of network interfaces that usually reside on multiple computers. The difference is that when packets are sent to a multicast address, they are sent to all of the network interfaces in the group. In contrast, when packets of data are sent to an anycast address, the packets are not sent to the entire group. Instead, they are only sent to the member that is in the closest physical proximity to the sender.

As you can see, there are at least some similarities between multicast and anycast addresses. In this article, I will conclude this series by discussing multicast and anycast addresses in more detail.

Multicast Addresses

As I explained earlier, multicast addresses are used to identify a group of network interfaces, known as a multicast group. These network interfaces are typically located on multiple computers, but this isn’t an absolute requirement. Multicast addresses are used to send information to any network interface that is defined as belonging to the multicast group.

One of the most interesting things about multicast addresses is that they are not mutually exclusive. Just because a network interface has a multicast address does not mean that the machine can not also have a unicast address or belong to other multicast groups. It is actually very common for a network interface to have a unicast address and to also be a member of multiple multicast groups. In fact, some operating systems add a computer’s network adapter to various multicast groups at the time that the network adapter’s unicast address is defined. For example, the Solaris operating system automatically adds network adapters to the Solicited Node and the All Nodes (or All Routers) multicast groups. In case you are unfamiliar with Solaris, the Solicited Node group is used for discovering other IPv6 enabled devices on the network. Windows Vista relies on a similar function.

Now that I have explained what multicast addresses are used for, I want to talk about what a multicast address looks like. Although an IPv6 address is 128 bits in length, it’s the first eight bits of the address that define an address as being a multicast address. Every multicast address uses a format prefix of 1111 1111. When expressed in colon hexadecimal notation a multicast address will always begin with FF.

The next four bits in a multicast address are known as flag bits. At the present time, the first three of these four bits are unused (and are therefore set to 0). The fourth flag bit is known as the transient bit. Its job is to express whether the address is a permanent or a temporary address. If the address is permanently assigned, this bit is set to 0, otherwise it is set to 1 to indicate that the address is transient (temporary).

The next four bits in a multicast address are known as the Scope ID bits. The amount of space reserved for the scope ID bits is 4 bits in length, which means that there are 16 different possible values. Although not all 16 available values are used at the present time, seven of these values are used to determine the address’ scope. For example, if an address has a global scope, then the address is valid across the entire Internet. The currently used scope ID bits are:

Decimal value          Binary Value              Address Scope

0                                  0000                            Reserved

1                                  0001                            Node-Local Scope

2                                  0010                            Link Local Scope

5                                  0101                            Site Local Scope

8                                  1000                            Organization Local Scope

14                                1110                            Global Scope

15                                1111                            Reserved

The remaining 112 bits make up the group ID. The group ID’s size allows multicast addresses to consume 1/256th of the total IPv6 address space.

To put this addressing scheme into prospective, I want to show you a few commonly used multicast addresses:

FF0x0:0:0:0:0:1
This is a multicast to all nodes. You might have noticed the X in the address, which is not a valid hexadecimal character. The X is a placeholder for the scope. This particular address can use the node local scope (FF01:0:0:0:0:0:1) or the link local scope (FF02:0:0:0:0:0:1).

FF0x:0:0:0:0:0:2
This multicast address is assigned to all routers within the defined scope. Again, the X in the address acts as a placeholder for the scope. Valid scopes are node local (FF01:0:0:0:0:0:2), Link Local (FF02:0:0:0:0:0:2), and site local (FF05:0:0:0:0:0:2).

Anycast Addresses

If you have some experience working with the IPv4 protocol, then you probably know that the concepts of unicast and multicast exist with the IPv4 protocol, although they are implemented differently. Anycast however, is unique to IPv6. Anycast works like a combination of unicast and multicast addresses. A unicast address is used to send data to one specific recipient, a multicast address is used to send data to a group of recipients, but an anycast address is used to send data to one specific recipient out of a group of recipients.

In case you are wondering, anycast was created as a way of making load balancing easier. Imagine a situation in which you need to provide a large number of users with access to either a service or to a router. In a situation like this, it often makes sense to use multiple servers to host the service that is being provided, or to use multiple routers, whichever the case may be. The reason is because doing so allows you to distribute the heavy workload among multiple devices so that no one single device is overwhelmed.

This type of load balancing is difficult to achieve using IPv4 (although it has been done). Using anycast addresses with IPv6 is an absolutely perfect solution to the need for load balancing. Think about it for a minute. You need to send a user request to one of many devices. You don’t really care which of the designated devices handles the request, as long as the request is taken care of. By using anycast addresses, each request is automatically sent to the device that is in the closest geographic proximity to the computer that is making the request. In certain situations, anycast can even be used to provide fault tolerance should a router fail. The failure can be detected, and requests can be redirected to the next closest router.

The most bizarre thing about anycast addresses is that there is no special addressing scheme. So far in this article series, you have seen that there are all sorts of rules governing the use and structure of unicast and multicast addresses. This simply isn’t the case with an anycast address. All you have to do to create an anycast address is to assign the same unicast address to multiple hosts. In doing so, the unicast address becomes an anycast address.

Conclusion

In this article series, I have tried to skim the basics of the IPv6 protocol. Most administrators probably won’t need to become IPv6 experts any time soon, but IPv6 is a required component in Windows Vista and Longhorn Server. As such, it makes sense to learn at least a little bit about it.