IP Protocol Versions

Two versions of IP are in use today: version 4 and version 6. IPv4 is the existing standard that was created in the late 1970s. IPv6 is the new standard.

IPv4

Three parts are used in configuring communication with IPv4: the IP address, subnet mask, and default gateway.

IP Address

IPv4 consists of 32-bit addresses, commonly expressed as dotted quads-four, 8-bit parts separated by periods; for example, 192.168.0.1. IPv4 has some problems, however, because the address space it provides is not large enough to handle the demand for addresses. This is partly due to the inefficient allocation of addresses. Many people are using private address and proxy servers to limit the number of public addresses being used. Still, with more and more machines connecting on the Internet, the IPv4 address space will run out at some point in time. IPv6 was created to resolve that problem by providing a larger address space from which to choose.

Subnet Mask

The subnet mask determines which parts of the IP address are the network and node portions. A subnet mask is another dotted quad address that 'masks' the portion of the IP address to determine where the break from network address to node address occurs. A typical subnet mask looks something like this: 255.255.255.0. Here, the first three octets are the network number and the last octet is the node number. Applying that to the IP address in our example, the following is true:

IP Address 192.168.0.1 Subnet Mask  255.255.255.0 Comparing this IP address and subnet mask, the network number is 192.168.0, and the node number is .1

For the purposes of this book, that's really all the details about IP addressing that you need to know. However, if you're curious, here's a little more technical information. The best way to represent IP addresses and subnet masks, and to understand the math behind how they work, is to represent them as binary numbers (1's and 0's):

• The IP address 192.168.0.1 would be represented in binary numbers as 110000.10101000.00000000.00000001

• The subnet mask 255.255.255.0 would be represented in binary numbers as 11111111.11111111.11111111.00000000

This subnet mask is also referred to as /24, because it contains 24 bits (1's). So if you see 192.168.0.0 /24, for example, you know the mask refers to the block of addresses from 192.168.0.0 through 192.168.0.255, and the subnet mask is 255.255.255.0. Now we can apply a more granular subnet mask here, remembering that the subnet mask for all devices has to be the same for them to be on the same network. The rule to follow is 'different subnet mask, different network.'

Default Gateway

Communicating to all the devices with the same network number is easy: just send out the packet, and it'll get there. Communicating across subnets is more involved, however, and this is where the default gateway comes in. The default gateway is an IP address of a device that resides on the same subnet. That device has more than one network connection, and it can 'route' packets from one subnet to another because it is aware of different connections.

IPv6

IPv6 has a 128-bit address space, which provides enough address space so that each square foot on the planet could have its own IP address with room to spare. IPv6 does have a long way to go before it becomes the protocol of choice, however, because IPv4 is deeply ingrained into every piece of networking. IPv6 support in Windows Server 2003 (WS03) is somewhat limited.

IPv6 addresses are commonly expressed as eight sets of 16-bit hex addresses (for example, FEAD:D8F1:FFA0:FAB7:1234:5678:9012:FF1A). As you can see, it's much larger than an IPv4 address and using it will make systems such as the DNS, which performs IP address to hostname resolution, all the more important. It's hard enough to remember the 4-octect IP addresses we use today; remembering eight 16-bit hex addresses is neigh impossible.

IPv6 can be configured automatically or manually. Automatic configuration has three options:

• Stateless Stateless configuration is accomplished through router advertisement messages. This is different than what occurs with DHCPv6. The router advertisements contain the information the client needs to set the IP address and default gateway information. This is the only type of auto configuration that WS03 supports.

• Stateful Stateful configuration is accomplished through the use of a configuration protocol, like DHCPv6, to obtain all the information needed to configure the interface.

• Both This option uses both a configuration protocol and router advertisements to configure the interface.

IPv6 has duplicate address detection built in. After a client gets the configuration information from the router advertisements, it performs the duplicate address detection. If that fails, the interface must be manually configured. If it succeeds, the client can use that address.

IPv6 is a rapidly developing protocol, and new Requests for Comments (RFCs) are emerging frequently. Support for IPv6 in WS03 is available, but it isn't the primary protocol WS03 was designed to use.