Because of the ever increasing amount of devices that require IP addresses, IPv4 addressing will no longer be enough to provide these devices with an IP address. IPv6 was introduced to solve the problems of the exhaustion of IPv4 addresses by increasing the IP address size from 32b to 128b. This allows for more than enough IP addresses to be given out and is no chance of them ever running out. In this report you will see the different ways in which IPv6 addresses can be assigned to host machines on a network whether it be statically or dynamically. There are benefits and also drawbacks for each method which will be covered in this report.
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What is IPV6?
IPv6 is an internet protocol which was developed to solve the problem of IPv4 address exhaustion. IPv4 uses 32b addressing so that means that it is 2^32 = 4,294,967,296 addresses. This may seem like more than enough IP addresses to provide everyone but in fact is not enough to keep up with the growing demand of IP addresses for the newer technology which requires IP addresses. IPv6 uses 128b addressing 2^128 = 340,282,366,920,938,463,463,374,607,431,768,211,456 addresses. 
As you can see there are a huge number of IPV6 addresses available which will almost never run out. Because of this it makes it harder for us humans to understand them in binary like in IPv4 so this is why with IPv6 they are changing to use hexadecimal instead of binary. By using hexadecimal it shortens the addresses to allot less than it would be if we kept on using binary but the drawback for this is that many people do not understand hexadecimal as most people havenâ€™t seen it implemented before.
Stateless auto configuration
The stateless auto configuration is when host machines on a network have the ability to configure themselves with a routable IP address without the need of a DHCP server to assign it an address. The way this is done is that hosts generate a link local address for each interface connected to it but like MAC and IP addresses the link local address must be unique for each host. To make sure that all of the link local addresses are unique the host machines send a neighbour solicitation message containing its possible link local address that it wants to use. If there is a reply then it means that another host has the same address that it wants to use and so must change its possible address and send the neighbour solicitation message again until it gets a unique address it can use on its interface.
Once the host has obtained a link local address its next aim is now to gain an IP address. To do this routers constantly send out router advertisements that hosts on the network listen out for and once the host receives an advertisement it then gains the network information to give its self an IP address to access the network.
Advantages of stateless auto configuration are that there is almost no configuration for the client to do when it the computer tries to gain an IP address. All the client needs to do is wait on the machine getting an IP address from the information gained from the router and that is all that is required to get up and running. Another benefit of stateless auto configuration is that it does not need a DHCP server in order for hosts to gain IP addresses and even if it needs to get other information later on it can then contact a DHCP server to get other information such as DNS server addresses.
A disadvantage of this method is that it doesnâ€™t get the entire network configuration that it may need to be fully functional on the network. Instead it uses DHCPv6 when it has enough configuration to get reach the DHCPv6 server to get the rest of the configuration. This is not good as it would be more efficient to get all of the needed configuration by using stateless auto configuration.
Stateful auto configuration
Stateful auto configuration is similar to DHCP in the way that IP addresses are given out to hosts on a network by using a server. Even though with IPv6 and its massive amounts of IP`s it is still a good idea to use a server to manage IP`s for companies to control and easily maintain what computers from each room or department are connected to the router. It also allows you to easily change the configuration of the network if needed from a central point in the network, this case being the DHCPv6 server and change settings such as the DNS server and the range of addresses to provide to hosts and this will also update to the clients when they are due to renew their lease.
Stateful auto configuration is used when there is no router on the link that is advertising router advertisements to provide the information to give its self an IP address. Instead it goes to a DHCP server that issues the host with all of the required configuration to get access to the network.
A disadvantage of stateful auto configuration is that it needs a DHCPv6 server in order to get an IP address and if the DHCPv6 server goes down then there is no way for hosts to get network configurations unless there is a router on the link that is advertising router advertisements. But in the worst case scenario when their being no router available then there is no way for hosts to get assigned an IP address.
DHCPv6 is the protocol that has been developed to work with IPv6. It allows for hosts on a network to gain an IP address and other settings like DNS and default gateway from the DHCPv6 server by using statefull DHCP. The hosts make contact to the DHCP server by using multicasts and also using the UDP protocol.
Below is information on the different messages that are exchanged between the host and the DHCP server in order for the host to gain a valid IPv6 address and get access to network resources with the address given to the host.
Solicit – This is when the client first makes contact with the DHCP server.
Advertise – This is when the DHCP server sends an advertise message saying that it is available to assign IP addresses to the client.
Request – The client machine now sends a request message to the server requesting an IP address and other information such as DNS, Default gateway.
Confirm – The client now sends a confirm message asking if the information is still valid since the IP address was given out.
Renew – This is when the clients DHCP lease time is running out and needs to be extended or given out a new IP address. With DHCP is it most likely during a renew process that the IP address will be extended to the client.
Rebind – This is similar to the renew message but with the rebind message the client contacts the server to increase its lease time but is also able to update any changes to other network configuration such as the DNS servers without changing its IP address
Reply – This is when the server sends a reply message with network configuration information in response to a solicit, request, renew and rebind messages received from the client before. The server then sends another reply message to confirm that the configuration that the client has received is appropriate for that network the client is connected to.
Release – The release message is used to indicate to the DHCP server that the client will no longer use the IP address and that the IP address the client had can go back into the address pool for another client to use.
Decline – The decline message is sent from the client to tell the DHCP server that the IP address given out from the server has already been assigned to another host on the network.
Reconfigure – This message is sent from the DHCP server to inform the client that there is new configuration on the network and the client must then send a renew and reply message in order to receive the updated information.
IPv6 is a vast improvement on the previous IPv4 protocol with the ability to provide almost unlimited IP addresses to hosts. The two ways in which hosts can gain an IP address are both adequate ways to distribute IP addresses but there are disadvantages with both stateful and stateless auto configuration. Because stateless requires that there must be a router that is advertising router adverts then it means that if there is no router then of course also means it cannot gain its IP address by using stateless configuration. Another disadvantage of this is that the router advertisements do not provide the hosts with all of the network configuration that it may need and then the host has to go to a DHCPv6 server using stateful configuration to get the rest of the configuration. There are also disadvantages for stateful addressing too in that if there is no DHCP server available then it cannot issue IP addresses to hosts.
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But out of the two auto configurations I would choose stateful to be the best method of issuing IP addresses because it allows for a remote server to distribute address and you can easily change the network settings on the DHCP server and it will also update the clients on the network. It also allows for more control on who gets what range of IP addresses and lets you easily manage IP`s to be issued to certain departments or rooms in a company so you can monitor the machines more easily.
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