Assigning IPv6 Addresses
This video will look at how an IPv6 node can automatically configure itself. There have been some improvements in IPv6 since IPv4 to allow configuration to occur with less infrastructure on the network.
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IPv6 Autoconfiguration
00:17 There are two different methods that can be used for an IPv6 node to be autoconfigured on the network. These are stateful and stateless. Stateful is when DHCP is used. It is called stateful because the DHCP server records the IP Address that was allocated to the node. The administrator can have a look at the DHCP server and see all the IP Addresses that have been allocated on the network. Stateless is different in that the nodes IP Address is not recorded on a system like DHCP. This means the node can configure itself with a valid IP Address on the network, however, the administrator does not know what the IP Address is. Thus the difference in name. With stateful the IP Address is recorded and with stateless the IP Address is not recorded. Stateless does not require services like DHCP to configure a node, and because of this, there are less options with stateless. Stateless will only provide very basic configuration. For example, additional options like DNS and booting from the network cannot be configured using stateless.
Link-local Address
02:05 In IPv6, a network interface is always assigned a Link-local address. When the network interface first starts up the Link-local address will be assigned to that network interface. The Link-local address can only access the local network and is used for some basic functions of IPv6. If the network interface is later on configured with an IPv6 address, the Link-local address is still used. The idea behind it is that the network interface will always have a valid IP Address that can be used for basic functions of IPv6 like network discovery. In IPv4, since there was no Link-local address, broadcast had to be used for the basic functions. In IPv6, broadcasts are not used since the Link-local address can be used to communicate on the network. The Link-local address will always start with fe80. After this, there are 54 bits of zeros. At the end of the address is the interface ID which after Windows XP is random. On Linux the interface ID will be the MAC address of the network interface. When the network interface first starts up and a Link-local address is assigned to it, the network interface will test the Link-local address on the network to ensure that it is unique. If there is another node on the network using the same Link-local address, a different Link-local address will be used.
Autoconfigured Address States
04:27 An IPv6 address has a number of different states that it goes through. When the network interface is first assigned an IP Address, the IP Address is placed in the ’Tentative’ state. In this state, a check is done on the network to see if the IP Address is in use. If the IP Address is not in use, the IP Address will change to the ’Preferred’ state. The preferred state means that the IP Address can be used to open new connections and accept connections. In some cases the IP Address many no longer be required. It is possible when configuring an IP Address to configure a valid life for it. In most cases this will be set to infinite. If a time period is set, the IP Address will change to ‘Deprecated’ when the time period expires. In some cases the IP Address may no longer be needed. For example, if the administrator changes the IP Address. When this occurs the IP Address will become deprecated. In the deprecated state, current connections can still be used but new connections should not be made to the IP Address. The idea behind this is, that if the network interface changes its IP Address, large transfers using the old IP Address should not be disrupted and given time to finish. This prevents network outages or connections being broken when the IP Address of the network interface is changed. If the state of the IP Address becomes invalid, the IP Address is no longer able to be used. To see the current states the command “NetSH Interface IPv6 show address” can be run.
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