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15 Identify the following address formats (IPv6, IPv4, MAC addressing)

Understanding MAC Addresses: It is important to understand the basic concepts of MAC addressing for a network administrator.

It is a 6 byte or in other words a 48 bit hexadecimal address. It allows NIC to be identified with a unique address. Irrespective of the protocol, it forms the basis of communication in a network. It has to ensure that no duplication of a MAC address takes place. To deal with this the assignment of MAB addresses is done by the Institute of Electrical and Electronics Engineers (IEEE).The IEEE followed a mechanism in which every manufacturer was assigned an ID and then allowing the manufacturer to allocate the ID's. As a result the first three bytes denote the manufacturer and the rest of the three are allocated by the manufacturer. The last three are known as Organizational Unique Identifier or OUI in short. Looking at an example; in the address 00:D0:59:09:07:51; 00:D0:59 are the first three bytes and stand for the manufacturer and 09:07:51 are the OUI.

There are different ways of finding out the MAC address of the NIC. The method undertaken to find out depends on the system or the platform on which work is being done. Some of the ways of finding out the address for various platforms are:

The winipcfg utility can be used:

The Run ipconfig / all from a command

The Run the ifconfig -a command can be

Use the Run the config command; and Run the show interface <interface name>

Understanding IPv4 Addressing: For a network using the TCP/IP protocol, each system needs to have a unique address. The address not only defines the network to which the device is connected, but also the address of the node on the network. It is mandatory for each device to share the same network address but different node address. The job of differentiating between the network address and the node address comes under the purview of a subnet mask. Without the differentiation done by the subnet mask, the IP address is nothing more but a number.

An IPv4 address comprises of four sets of 8 bits, or octets. It comes out to be a 32 bit address in length. A decimal value is assigned to every bit in each octet. The values are assigned from left to right, with the leftmost having the highest value of 128, which is followed by 64, 3 2, 1 6, 8, 4, 2, and 1, as one goes right.

Values are attached to every bit in the octet following the binary system, that is, the value of a bit can be a 1 or a 0. The decimal value of every 1 is counted, whereas the 0 are ignored. This numbering system is called binary. If the value is 1, it is counted as its equivalent decimal value, and if it is 0, it is ignored. This means that if all the bits are 0, the value of the octet is 0. If all the bits in the octet are 1, the value of the octet will be 255. The value 255 is derived by adding up 128+64+32+16+8+4+2+1. The binary to decimal conversions are depicted in the table given below.

Decimal Value	128	64	32	16	8	4	2	1
Binary Value	1	1	1	1	1	1	1	1

Figure 43: Binary to Decimal Conversion

By using the set of 8 bits and manipulating the 1s and 0s, any value between 0 and 255 can be obtained for each octet. Table 5.2 shows a few examples of this.

The address is arranged in four sets of bits, with each set separated from the other by using period. IP addresses are grouped in classes. Classes are based on logical divisions. There are five classes: A, B, C, D, and E available in IPv4 address. For assigning addresses to clients only the first three classes are used. A fixed length subnet mask is used each for differentiating between the network address and the node address. The first octet is used by a Class A addresses, two octets are used by a Class B addresses, and three octets are used by a Class C addresses. This results in Class A having a small number of network addresses but a large number of host addresses. Class B has larger number of networks but smaller number of hosts. Class C has even a larger number of networks and a smaller number of hosts. Whereas Class E is reserved for future development, Class D is reserved for multicast addressing. The numbers are represented in the table given below:

Address Class	Range	Number of Networks	Number of Hosts/Network	Binary Value of First Octet
A	1-126	126	16,777,214	00000001 01111110
B	128-191	16384	65,534	10xxxxxx
C	192-223	2,097,152	254	110xxxxx
D	224-239	N.A	N.A.	1110xxxx
E	240-255	N.A	N.A.	1111xxxx

Table 5: IPv4 Address Classes and the Number of Available Network/Host

Addresses

The network number 127 is kept as reserved for a local loopback. The local loopback is a function built in to the TCP/IP protocol. It is an inbuilt function in the TCP/IP protocol suite and can be used for troubleshooting.

Understanding IPv6 Addressing: IPv4 has served its purpose well for nearly 30 years. When Ipv4 addresses were developed the need for IP addresses could not have been predicted. The 4,294,967,296 options provided by the 32 bit scheme of IPv4 addresses approached exhaustion at a much faster rate than thought, and as a result the IPv6 was developed in the mid 1990's. IPv6 scores over IPv4 when it comes to its ability to handle growth for public networks. It uses 128 bits for addressing and as a result the options available for multifold.

An IPv6 is divided into 16 sets, with each 16-bit block converted in to a 4 digit hexadecimal number, separated by semicolons. The result is given the name of colon-hexadecimal.

Two IPv6 addresses are listed in Figure 5.5: the link local IPv6 address, which we discuss later, and the external IPv6 address. The external IPv6 address is 2001:0:4137:9e50:3cde:37d1:3 f57:fe93. You can simplify an IPv6 address by removing the leading zeros within each 16-bit block. All zeros cannot be removed, however, because each address block must have at least a single digit. The address shown in Figure 5.5 suppresses the zeros. Removing the zero suppression, the address representation becomes 2001:0000:413 7:9e50:3cde:3 7d1:3f57:fe93

Some of the IPv6 addresses you will work with have sequences of zeros. When this occurs the number is often abbreviated to make it easier to read. In the preceding example we saw that a single zero represented a number set in the hexadecimal form. To further simplify the representation of IPv6 addresses, a contiguous sequence of 16-bit blocks set to 0 in the colon hexadecimal format can be compressed to "::", known as double-colon. For example, you can compress the IPv6 address of 2001:0000:0000:0000:3cde:37d1:3f57:fe93 to 2001::3cde:37d1:3f57:fe93.

However, there are limits to how we can reduce the IPv6 zeros. Zeros within the IPv6 address cannot be eliminated when they are not first in the number sequence. For instance, 2001:4000:0000:0000:0000:0000:0000:0003 cannot be compressed as 2001:4::3. This would actually appear as 2001:4000::3.

The formula used for deriving the numbers that are represented, from the number 8 subtract the number of blocks and subsequently multiply by 16. In the address 2001:4000::3, the three blocks are 2001, 4000 and 3. The equation according to the formula mentioned above will be 8-3x16=80.

So in the address 2001:4000::3, there are three blocks used (2001, 4000, and 3). The equation is 8-3*1 6=80. The number of bits represented by the double colon is 80.

Differences between Address Type of IPv4 and IPv6: There are several types of addresses available in both the versions.

Starting with IPv6:

- Unicast IPv6 Addresses: This type of address specifies a single interface. It is a direct line communication and data packets sent to a unicast destination travel from the sending host to the destination host. The unicast addresses are further of the following type:

- Global Unicast Address: This type is equal to an IPv4 public address. These are routable address having the ability to travel through the entire network. 2000::/3 is used as a prefix for these addresses.

- Link-Local Address: These addresses are designated to be used on a single local network. These addresses are configured on all interfaces automatically and are considered equal to 169.254.0.0/16, which is again an automatically assigned IPv4 addressing. fe80::/10 is used as a prefix for these address types. They form a communication between devices which are on the link

- Unique Local Address: These addresses are also equivalent to IPv4 addresses belonging to the private address spaces 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. These do not interfere with the global unicast addresses. This address is not circulated outside the site. These are assigned through stateless or stateful address configuration processes. FC00::/7, is the prefix that is used for these addresses.

- Multicast Addresses: Just as in the case of IPv4 addresses, multicasting in version 6 also sends and receives data. It does this between groups of nodes. The IP messages may be sent to a specific group or to a single node. FF00::/8, is the prefix used for these addresses..

- Anycast Addresses: These addresses are for the middle ground falling between the unicast addresses and multicast addresses. This address delivers messages to a single node in the multicast group.

IPv4 Address Types:

In this version there are primarily three types of addresses available. These are:

- Unicast: Specification of a single address is done in these types of addresses. It is a point to point to link and the data is sent to a specific node identified by the address.

- Broadcast: Broadcast is an absolute opposite of unicast addressing. It allows for targeting a number of networks at the same time. It is transmitted to everyone present on the network.

- Multicast: It is based on the technique, which allows sending and receiving of data between the members of a group at a given point of time. The messages are sent to the entire group at one time than being sent individually.