Windows 7 : Networking with TCP/IP (part 2) - Understanding IPv6 & Configuring IPv4, IPv6, and Other Protocols

3. Understanding IPv6

Although IPv4 allows for more than four billion networked computers and devices, the world is running out of available IPv4 addresses. Rather than allow there to be a shortage of available addresses, organizations have worked together to create several solutions to the problem. One of these solutions is IPv6. Unlike IPv4, which uses 32-bit addresses, IPv6 uses 128-bit addresses, which offer literally enough IP addresses so that there are thousands of IP addresses for each square yard of the Earth’s surface. Or put another way, there are about 340,282,367,000,000,000,000,000,000,000,000,000,000 available addresses—give or take a few hundred million quadrillion.

To make it easier to track all those IP addresses, IPv6 uses hexadecimal numbers rather than decimal numbers to define the address space. This means that instead of allowing only the numbers 0 through 9 for each position in the IP address, IPv6 allows the values 0 through 9 and A through F, with A representing 10, B representing 11, and so on, up to F representing 15. Thus, the values 0 through 15 can be represented using the values 0 through F.

IPv6’s 128-bit addresses are divided into eight 16-bit blocks delimited by colons. With standard IPv6 addresses, the first 64 bits represent the network ID and the last 64 bits represent the network interface being used. Since many IPv6 address blocks are set to 0, a contiguous set of 0 blocks can be expressed as ::, a notation referred to as the double-colon notation. Table 4 shows an example of an IPv6 IP address and an abbreviated IP address.

Table 5. IPv6 address example

IPv6 address	Abbreviated IPv6 address
FE80:0:0:033C:FB:B335:FE4F:752B	FE80::033C:FB:B335:FE4F:752B

Just as there are different types of IPv4 addresses, there are different types of IPv6 addresses. As Table 6 shows, the type of an IPv6 address is identified by the high-order bits of the address. The IPv6 address 0:0:0:0:0:0:0:1 is used for local loopback. IPv6 addresses beginning with FF00 are used for multicast transmissions. IPv6 addresses beginning with FE80 are used for link-local unicast transmissions. Link-local unicast IPv6 addresses are the equivalent of IPv4 automatic private addresses. IPv6 addresses beginning with FEC0 are used for site-local unicast transmissions. Site-local unicast IPv6 addresses are the equivalent of IPv4 private addresses. Global unicast IPv6 addresses are the equivalent of IPv4 public addresses because they are globally reachable on the Internet and must be assigned by an IP address authority.

Table 6. IPv6 subnet prefix example

IPv6 subnet prefix length	Associated network addresses
2001:1234:5678::/48	2001:1234:5678:: through address 2001:1234:5678::FFFF:FFFF:FFFF:FFFF

IPv6 doesn’t use subnet masks to identify which bits belong to the network ID and which bits belong to the host ID. Instead, each IPv6 address is assigned a subnet prefix length that specifies how the bits in the network ID are used. The subnet prefix length is represented in decimal form. For example, if 48 bits in the network ID are used, the subnet prefix length is written as /48. Table 7 shows an example of the subnet prefix length and the associated network range.

Table 7. IPv6 address types

Address type	Binary prefix	IPv6 notation
Unspecified	000000	::/128
Loopback	000001	::1/128
Multicast	11111111	FF00::/8
Link-Local unicast	1111111010	FE80::/10
Global unicast	All other addresses

IPv6 allows for a greater than 64 KB payload in an IPv4 packet, which designers refer to as a jumbogram. These jumbograms greatly increase the throughput of high-performance networks. IPv4 does not support this type of transmission, and it has a 64 KB payload limit.

IPv6 packets are composed of two parts: a header and a payload section. The first 40 octets of an IPv6 packet contain the header, composed of the source and destination addresses, including an IPv4 version where necessary, traffic class section, flow label (for packet priority information), payload length, next header addressing section, and hop limit. The payload section consists of the actual data sent during transmission. The payload section can contain either 64 KB of information, like the IPv4 standard, or a jumbogram for true IPv6 “high-throughput” networking architectures. Table 8 shows an example of an IPv6 packet.

Table 8. IPv6 packet example

+	Bits 0–3	4–7	8–11	12–15	16–19	20–23	24–27	28
0	Version	Traffic class		Flow Label
32	Payload Length				Next Header		Hop Limit
64	Source address information
192	Destination address information

NOTE

IPv6 developers also implemented IP Security (IPSec) into the protocol. IPSec lies within the IP network layer, and encrypts and authenticates as an integrated part of the protocol by default. This eliminates additional overhead in encoding and decoding packets using IPSec functionality.

4. Configuring IPv4, IPv6, and Other Protocols

Each network adapter configured on your computer has a separate IP addressing configuration, which you can manage through the associated network connection. The network connection for the first network adapter on the computer is named Local Area Connection; the second network adapter is named Local Area Connection 2, and so on. Connections for wireless, dial-up, or broadband have either default names or the names you assigned when you created the connection.

During installation of the operating system, the Setup program automatically installed the necessary networking components for your computer if a network adapter was detected. In addition to TCP/IPv4 and TCP/IPv6, Windows 7 uses the following networking components:

Client for Microsoft Networks

Allows you to connect to Microsoft-based networking services. If you are connecting to a Windows domain, you are required to use this protocol.

QoS Packet Scheduler

Offers the capability to define which protocols and applications have precedence in a situation where multiple applications or protocols request access to the same network resources. This protocol gives you the ability to raise or lower the priority of the requests made. Basically, the Quality of Service (QoS) Packet Scheduler works as a traffic cop by allowing you to control the rate of flow and prioritization of services available.

File and Printer Sharing for Microsoft Networks

Allows other computers to connect to and access resources on your computer when using Microsoft networking protocols. This feature also allows you to access resources on remote machines connected to your network and on the Internet.

Link-Layer Topology Discovery Mapper I/O Driver

Allows your computer to discover and locate other computers and devices on the network. Also used to determine the available network bandwidth.

Link-Layer Topology Discovery Responder

Allows your computer to be discovered and located by other computers and devices on the network.

Although you will probably use only IPv4 on your home or small-office network, you should understand how IPv6 works and be able to configure the protocol. You can manually assign IPv4 and IPv6 addresses using static IP addresses, or automatically assign them using dynamic IP addresses. You configure the IPv4 and IPv6 protocols in exactly the same way, with the following exceptions:

• IPv4 uses subnet masks, and IPv6 uses subnet prefix lengths.

• IPv4 uses both DNS and WINS for locating computers and devices on the network, and IPv6 uses only DNS.

• IPv4 allows for automatic private IP addressing if a DHCP server cannot be located, and IPv6 simply assigns the computer a link-local unicast (private) IP address based on the MAC address of the network adapter.

On a per-network-connection basis, you can configure the networking protocols used by completing the following steps:

1. Click Start, and then click Control Panel.

2. In the Control Panel, click Network and Internet→Network and Sharing Center.

3. In the Network and Sharing Center, click “Change adapter settings.” This opens the Network Connections window.

4. Right-click the network connection you want to configure and then select Properties. This displays a Properties dialog box, as shown in Figure 1.

Figure 1. Configuring connection properties

1. On the Networking tab, you can use the checkboxes provided to manipulate the different protocols associated with the network adapter. You can turn the different protocols on and off by clicking the checkbox associated with each protocol:

   • If you are using file and printer sharing on your network, you must enable both Client for Microsoft Networks, and File and Printer Sharing for Microsoft Networks.

   • The QoS protocol offers greater flexibility in the flow of data by prioritizing the different requests made by the client.

   • If you are using the IPv6 protocol for connectivity, you also must use the QoS Packet Scheduler, which Windows selects by default. If you are not using this protocol, you should disable it by unchecking the box associated with this protocol.

   • If you are using the IPv4 protocol for connectivity, you must leave the Internet Protocol version 4 (TCP/IPv4) box checked.

   • If you are using the IPv6 protocol for connectivity, you must leave the Internet Protocol version 6 (TCP/IPv6) box checked.

   • If you want to be able to use the network connection to discover and locate other computers and devices, you must leave the Link-Layer Topology Discovery Mapper I/O Driver box checked.

   • If you want other people to be able to discover your computer through the network connection, you must leave the Link-Layer Topology Discovery Responder box checked.

NOTE

Although the discovery protocols add some overhead to your computer, they offer some real value to the capabilities of networking in Windows 7. Most of the time, you should leave these protocols enabled, unless you are leery of security issues associated with other people discovering your computer. If you are concerned about the security aspects, verify that you have Windows Firewall enabled on your computer and make sure the hardware firewall on your Ethernet router is properly configured. Although firewalls will not eliminate all problems associated with security, they will drastically decrease the potential to have data stolen.

1. To configure IPv4 or IPv6, double-click Internet Protocol version 4 (TCP/IPv4) or Internet Protocol version 6 (TCP/IPv6) as appropriate. As Figure 2 shows, the options available are nearly identical whether you are working with IPv4 or IPv6. Repeat this as necessary to configure both IPv4 and IPv6.

Figure 2. Configuring IPv4 and IPv6

1. The General tab allows you to select either “Obtain an IP address automatically” or “Use the following IP address.” If you have enabled DHCP on a network device such as a router, you should choose the first option. This allows DHCP to configure the options of the protocol for IP addressing and the default gateway for accessing the network. You should also choose “Obtain DNS server addresses automatically” to ensure that your computer gets the correct DNS servers for name lookups. Windows 7 defaults to the automatic configuration, as you’ll typically have a device providing your IP addressing dynamically.

2. To configure the network adapter to use a manually assigned IP address, do the following:

   1. Select the “Use the following IP address” option. For IPv4 addressing, enter the IP address you want to associate with the network adapter in the “IP address” text box and then enter the subnet mask in the “Subnet mask” text box. For IPv6 addressing, enter the IP address in the IP address text box and then enter the subnet prefix in the “Subnet prefix length” text box.

   2. Select the “Use the following DNS server addresses” options. Enter the DNS server address of either your local DNS server or your ISP into the “Preferred DNS server” text box. If you have additional DNS server information to provide, enter the address into the “Alternate DNS server” text box.

3. Click OK to save your settings.

NOTE

If you are manually configuring your IP address, you must have an IP address, subnet mask or subnet prefix, and IP addresses for DNS servers. If you have a computer that connects to a network router that in turn connects to your ISP’s cable/DSL modem, you should configure private IP addresses for your internal network. When enabling network connectivity without a hardware firewall, you should verify that Windows Firewall is on. You should also carefully consider whether you need file and printer sharing. Enabling file and printer sharing without a firewall may make your computer accessible to other people.