Menu

June 2019

Why We Need IPv6?

Why We Need IPv6?

/ /

Why do we need IPv6? Due to the massive increase in devices accessing the Internet, each device needs a unique IP address to access the network and Internet. The number of devices has risen from stationary to mobile, generally requiring an Internet connection.

Because of the vast increase, IPv4 addresses are running out of space and needs an IPv6 address to accommodate the increased demand due to larger address space, along with improved traffic routing and better security.

We are currently using IPv4 on the Internet. It was developed in the early ’70s to facilitate communication and information sharing between government researchers and academics in the US. Due to a limited number of access points, the IPv4 address space is enough, and the developers didn’t imagine requirements such as security or quality of service. IPv4 has continued for over 40 years and has been an important part of the Internet uprising.

Need IPv6 Due to Shortage of IPv4

The most understandable answer to the need for IPv6 is that IPv4 addresses are out of space. Because IPv4 has only 4.3 billion addresses, Researchers have adopted many methods to improve the reduction of IPv4 addresses, including Subnetting, VLSM, and NAT. Still, these methods could not provide the ability to scale networks for future demands. The reduction of IPv4 address space has been the motivating factor for moving to the next-generation internet protocol.

The IPv6 addresses satisfy the increasing and complex requirements of a hierarchical and limitless supply of IP addressing. Because IPv6 provides 340 undecillion addresses. That is 340 times 10 to the 36th power or 340 trillion trillion trillion possible IP addresses.

Efficiency

IPv6 simplifies and speeds up data transmission because packet handling is more efficient and removes the need to check packet integrity. It also frees router time that can be better spent moving data. IPv6 also eliminates the address conflict issues which is common under IPv4 and enables smooth connections and communication for network devices.

Security

IPv6 was built with security hazards in mind. Many of the security features have been added to the IPv6 address default, which is optional for IPv4 addresses. IPv6 encrypts traffic and checks packet integrity to protect standard Internet traffic more efficiently.

The IPSec provides privacy, authentication and data integrity. Because of their potential to carry malware, corporate firewalls often block IPv4 ICMP packets, but ICMPv6, implementing the Internet Control Message Protocol for IPv6, may be permitted because IPSec can be applied to the ICMPv6 packets.

Special-Purpose IPv4 Addresses

Special-Purpose IPv4 Addresses

/ /

Many Special-purpose IPv4 addresses are reserved for different applications. For example, we cannot assign network and broadcast addresses to hosts on the network. However, some addresses are reserved as particular addresses that we can allot to hosts in the network, with some limitations on how those hosts interact within the network.

Special-Purpose Loopback addresses

The IP address 127.0.0.0/8  is a special-purpose IPv4 address called localhost or loopback address. 127.0.0.1 is usually used as “the” loopback address, but the rest of the block should also loopback, meaning that the block is not used for anything. For example, most Cisco switches use 127.0.0.xx IPs to listen for attached cards and modules, so at least some other addresses are in use.

In most cases, the IP address 127.0.0.1 is reserved for use on personal computer loopback testing. The host uses the loopback IP address to direct traffic to itself. For example, we can use the loopback IP address to test whether the TCP/IP configuration is operational. Network software and utilities also use 127.0.0.1 to access a local computer’s TCP/IP network resources.

Messages destined to loopback addresses do not reach outside the local area network (LAN) but instead are automatically rerouted by the computer’s own network adapter back to the receiving end of the TCP/IP stack. All computers use this IP address as their own IP address, but it doesn’t let them communicate with other devices as a real IP address does.

The Computer uses this particular IP address in exceptional circumstances. For example, a web server running on a computer can point to 127.0.0.1 to run the pages locally and tested before deployment. This is unlike a regular IP address that transfers files to and from other networked devices.

Special-Purpose Link-Local addresses

Link-local addresses are mostly assigned automatically using operating system procedures, but we can also assign Them manually. Normally, Link-Local addresses are only used when no mechanism of address configuration exists, such as DHCP, or when another configuration method has failed. The addresses are also known as Automatic Private IP Addressing (APIPA).

It can be used to communicate with two hosts on the same link when no other IP address is specified. In other words, when the system starts up, the operating system tries to configure an address on its interface through various methods, such as Dynamic Host Configuration Protocol (DHCP) and Manual Configuration.

Suppose the Operating System fails to configure an IP address on the interface through any of the IP address configuration methods. In that case, it configures an address on the interface from the link-local pool, which is 169.254.0.0/16 in IPv4 address space.

TEST-NET addresses

These addresses are set aside for teaching and learning purposes. Address prefixes listed in Test-Net addresses and other Special-Purpose Address Registry are not guaranteed any refutability in any particular local or global network. The following ranges are reserved for specific purposes In RFC-5737.

192.0.2.0/24TEST-NET-1RFC 5737
192.0.2.0/24 TEST-NET-1 RFC 5737
203.0.113.0/24TEST-NET-3RFC 5737

Default Router Address

The default route is the gateway of last resort used to forward packets whose destination address does not match any route in the routing table. The CIDR notation for a default route is 0.0.0.0/0. So when both the host and network portion and the prefix length are zero, a default route is the shortest possible match. So, when a packet does not match any route in the routing table, it will match a default route, the shortest possible route, if it exists in the routing table.

A default route is beneficial in networking where learning all the routes is not desirable, such as in the case of stub networks. A default route is valid when a router is connected to the Internet. Without a default route, the router must need the routing entry for all networks on the Internet. The internet network is in numbers of several hundred thousand. However, we can configure it with a single route.

Conclusion

In conclusion, there are several special-purpose IPv4 addresses that are reserved for different applications. These addresses have specific uses and limitations within a network.

The loopback address, represented by the IP address 127.0.0.0/8, is a special-purpose IPv4 address called localhost or loopback address. The most commonly used loopback address is 127.0.0.1, but the entire block is reserved for loopback purposes. It is used for testing network configurations and accessing local TCP/IP network resources on a personal computer. Messages sent to loopback addresses do not leave the local area network (LAN) and are automatically rerouted back to the receiving end of the TCP/IP stack

Link-local addresses, also known as Automatic Private IP Addressing (APIPA), are assigned automatically by operating systems when no other address configuration method is available. The range for link-local addresses is 169.254.0.0/16 in the IPv4 address space. These addresses are used for communication between hosts on the same link when no other IP address is specified

There are also special-purpose addresses reserved for teaching and learning purposes, known as TEST-NET addresses. These addresses are not guaranteed to be routable in any particular network and are used for educational purposes. Examples of TEST-NET addresses include 192.0.2.0/24 and 203.0.113.0/24.

Lastly, the default router address, also known as the default route, is used to forward packets whose destination address does not match any route in the routing table. The CIDR notation for a default route is 0.0.0.0/0. It is beneficial in networking scenarios where learning all the routes is not desirable, such as in stub networks

FAQs

Q1: What is the loopback address used for?

The loopback address, represented by the IP address 127.0.0.0/8, is used for testing network configurations and accessing local TCP/IP network resources on a personal computer. It allows a host to direct traffic to itself and is commonly used to test whether the TCP/IP configuration is operational

Q2: Can loopback addresses communicate with other devices on the network?

No, loopback addresses do not communicate with other devices on the network. Messages sent to loopback addresses do not leave the local area network (LAN) and are automatically rerouted back to the receiving end of the TCP/IP stack

Q3: What are link-local addresses used for?

Link-local addresses, also known as Automatic Private IP Addressing (APIPA), are used for communication between hosts on the same link when no other IP address is specified. These addresses are assigned automatically by operating systems when no other address configuration method is available.

Q4: What are TEST-NET addresses used for?

TEST-NET addresses are reserved for teaching and learning purposes. They are not guaranteed to be routable in any particular network and are used for educational purposes

Q5: What is the default router address used for?

The default router address, also known as the default route, is used to forward packets whose destination address does not match any route in the routing table. It is beneficial in networking scenarios where learning all the routes is not desirable, such as in stub networks

Classful and Classless IP Addressing – Exclusive Details

Classful and Classless IP Addressing – Exclusive Details

/ /

Classful Addressing

The IETF published the first major addressing scheme in September 1981 in RFC 790. The IP addressing scheme was 32 bits long and had three classes, A, B, and C, corresponding to 8-bit, 16-bit, and 24-bit prefixes. No other prefix lengths were allowed then, and there was no concept of nesting a group of 24-bit prefixes, such as within a 16-bit prefix.

Class D and E addresses were also defined, but neither of these two address classes was normally used. Class D addresses are reserved for multicasting, and Class E addresses are reserved for experimental and future use. The easiest way to distinguish between different address classes is to use the first decimal number in the IP address. Classful networks use the classful subnet mask according to the leading bits in the first block of the IP address. The figure below illustrates the key information of the Classful address scheme.

classful

Class A (0.0.0.0 to 127.255.255.255)

The default subnet mask for this class is 255.0.0.0 or /8. This class supports an extremely large network with more than 16 million hosts. The first octet’s high-order bits of Class A addresses are zero, so the remaining 7 bits create 128 possible Class A networks. 0.0.0.0 is used for the default router, and the 127.0.0.0 network is reserved for local loop testing. So, the remaining network is from 1 – 126 total 126 networks.

Class B (128.0.0.0 – 191.255.255.255)

The default subnet mask for the class b network is 255.255.0.0 or /16. Class b network support supports large networks with up to 65,000 host addresses. The high-order bits for the class b network are 10 in the first octet, and the remaining bits of the first 2 octets create over 16,000 networks. The network 169.254.0.0 is a special network for link-local addresses, also known as Automatic Private IP Addressing (APIPA).

Class C (192.0.0.0 – 223.255.255.255)

The default subnet mask for a Class C network is 255.255.255.0 or /24. Class C supports small networks with a maximum of 254 hosts. The first three bits of the octet indicate the high-order bit of the class. The remaining bits of the first three octets indicate the network and the fourth indicates host addresses in this class. The high-order bit is 110. A Class C address has over 2 million possible networks.

Class D (224.0.0.0 – 239.255.255.255)

The first four bits of the first octet in Class D IP addresses are high-order bits (HOB); the first four bits are 1110. The range of Class D addresses starts from 224.0.0.0 to 239.255.255.255. Class D is reserved for multicasting. In multicast communication, data is destined for multiple hosts, not for a particular host. The class has no subnet defined.

Class E (240.0.0.0 – 255.255.255.254)

The first five bits of the first octet are reserved HOB for Class E address. The HOB for Class E is 11111. The address range is 240.0.0.0 to 255.255.255.254. This class is reserved for experimental purposes only, such as R&D and study. Class E is also not equipped with a subnet mask like Class D.

Public IP Addresses

A public IP address range is defined for network devices, hosts, and servers like web servers and email servers to allow direct access to the Internet. Any server device using public IP addresses directly accessible from the Internet. A public IP address is globally unique and can only be assigned once to any device worldwide. Every device accessing the internet is using a unique IP address. Public IP addresses are also required for any publicly accessible network hardware, such as servers hosting websites. Public addresses are globally routed between different ISPs and routers. However, some addresses are not routable on the Internet. These addresses are called private addresses.

Private IP addresses

Private IPv4 addresses were introduced in 1990 because of reduced IPv4 addresses. The Private addresses are not unique and can be used repeatedly for internal networks. The computers at home, tablets, smartphones, network printers, and the computers within organizations are generally assigned private IP addresses. A computer with a private IP address can see and access the local network through its private IP address.

The computer and devices with a private IP address cannot directly access and communicate via the private IP address; however, using the router’s public IP addresses, the devices outside a private network can communicate. The NAT allows direct access to a local device assigned a private IP address. The range of private IP addresses is defined for all three classes.

10.0.0.0 /8 or 10.0.0.0 to 10.255.255.255

172.16.0.0 /12 or 172.16.0.0 to 172.31.255.255

192.168.0.0 /16 or 192.168.0.0 to 192.168.255.255

Classless Addressing

Classful addressing divides an IP address into the Network and Host portions along octet boundaries. It uses a fixed subnet mask, which is /8, /16 and /24, but classless addresses use a variable number of bits for the network and host portions of the address. The subnet mask is not fixed for a classless addressing system.

The classful addressing system assigned 50% of IPv4 addresses to Class A networks, 25% of IPv4 addresses to Class B, 12.5% of IPv4 addresses to Class C, and the remaining 12.5 % Shared to both Class D and E. The classful addressing plan wastes the most IP addresses, decreasing the availability of IPv4 addresses. For example, an organization with a network with more than 254 hosts would need a class B network with more than 65,000 addresses, wasting 64,700 IP addresses.

IETF introduced classless addressing to overcome the waste of IP addresses in 1993. There is no IP address class in a classless addressing system, but the addresses are still granted in blocks. In a classless addressing system, when an organization or individuals need connectivity to the Internet, it also grants a block or range of addresses according to the needs of the organization and individuals. For example, an individual requires only two addresses, and an organization is given thousands of addresses based on the number of its requirements.

Unicast

Unicast, Multicast and Broadcast Communication

/ /

Devices in the network can send data over the network using communication techniques known as Unicast, Multicast and Broadcast. Unicast is sending a data packet from one host to an individual host. The Broadcast technique sends a data packet from one host to all hosts in the network. In the Multicast technique, a packet is sent from one host to a group of hosts, not to all hosts, possibly in different networks. In all cases, the packet header must contain the originating host address as the source address.

Unicast

In the unicast technique, communication occurs between host-to-host over the network. The packet in unicast transmission contains the destination device address as a destination address and can be routed through Internetwork. There is just one sender and one receiver in unicast communication.

The addresses assigned to two end devices are the source and destination addresses in IPv4 unicast communication. The sending host device encapsulates its IPv4 address as a source host address and the destination host address as the destination address during the encapsulation process. The range of IPv4 unicast addresses is from 0.0.0.0 to 223.255.255.255, but inside this range, many addresses are reserved for special purposes.  Remember that any packet’s source address is always the originating host’s unicast address. The figure below illustrates the unicast communication.

Unicast

Multicast

Multicast is another communication technique used in networking. In multicasting, the data packet is sent from one or more hosts to a group of hosts. There are possibly one or more senders, and the information is distributed to a group of receivers. It reduces traffic by allowing a host to send a single packet to a selected set of hosts that are multicast group members.  The IPv4 address range 224.0.0.0 to 239.255.255.255 is reserved for multicasting.

A router connected to the local network knows about the multicast packet destinations. So, the router forwards the packets to the multicast group and never forwards them further. A typical use of the reserved multicast address is in routing protocols is to exchange routing information. For example, 224.0.0.5 and 224.0.0.6 are reserved for OSPF, and 224.0.0.9 is reserved for RIP version 2. The figure below illustrates the multicast communication.

Multicast

The multicast client can receive multicast data using client program services. Each multicast group is its own IPv4 multicast destination address. When a host subscribes to a multicast group, the host processes packets addressed to this multicast address and packets to its uniquely allocated unicast address. Some important reserved multicast addresses are the following:-

224.0.0.0Base address
224.0.0.1Reserved for all hosts on the same network segment.
224.0.0.2Reserved for all Routers multicast group addresses on the same network segment.
224.0.0.4Distance Vector Multicast Routing Protocol (DVMRP) multicast routers address.
224.0.0.5Reserved for all OSPF Routers for sending Hello packets to all OSPF routers on a network segment.
224.0.0.6Reserved for sending OSPF routing information to designated routers (DR) on a network segment.
224.0.0.9The RIP version 2 group address used to send routing information to all RIP2 routers on a network segment.
224.0.0.10Reserved for EIGRP group address to send routing information to all EIGRP routers on a network segment.
224.0.0.18Reserved for Virtual Router Redundancy Protocol (VRRP)
224.0.0.19–21Reserved for IS-IS over IP
224.0.0.102Reserved for Hot Standby Router Protocol version 2 (HSRPv2) and Gateway Load Balancing Protocol (GLBP)
224.0.0.251Reserved for Multicast DNS address
224.0.0.252Reserved for Link-local Multicast Name Resolution address
224.0.1.1The RIP version 2 group address sends routing information to all RIP2 routers on a network segment.
224.0.1.41H.323 Gatekeeper address

Broadcast

In broadcast communication, one host sends a packet to all other hosts over the network. There is only one sender in the broadcast process, but the data is received by all other connected hosts in the network. The source sends data to all hosts in the network using a broadcast address. The broadcast packet contains the destination IPv4 address with all ones in the host portion. All 1s in the host portion means the whole local network will receive the packet.

Network protocols also use the broadcast technique, such as DHCP. When a host receives a packet sent to the network broadcast address, the host processes this packet as it would a packet received to its unicast address. Another example of the broadcast is Wi-Fi networks, which declare themselves to all nearby wireless devices using a broadcast technique. Wi-Fi broadcasts their SSID to make it easier for users to find a nearby network.

There are two types of broadcast: directed and limited. A directed broadcast sends traffic to all hosts on a particular network. For example, a host on the 200.100.50.0/24 network sends a packet to 200.100.50.255. This is a routable address, so a router would forward it to the end destination gateway if the router is configured to do so. But a limited broadcast is sent to 255.255.255.255.  The router will send the traffic received to this address to all other hosts on the local network.  255.255.255.255 is not a routable address, so a router would not route the traffic outside the local network. By default, routers do not forward broadcasts.

Broadcast traffic takes network resources because each host on the network must process the broadcast packet. So, broadcasting affects the network and devices’ efficiency. Therefore, broadcast traffic is limited and does not affect the performance of the network and network devices. Routers discourage broadcasting by default, because each port of the router has separate broadcast domains, subdividing of networks also improve the network’s performance. The figure below illustrates the broadcast communication.

Broadcast
prefix

Prefix, network, broadcast and host address

/ /

The Prefix Length

Expressing network and host addresses with the dotted decimal subnet mask address is difficult. So, convert the dotted-decimal representation of the subnet mask to binary and count the number of adjacent 1s bits, starting at the most significant bit in the first octet. The number of 1s in the subnet mask is called a prefix. The prefix is written in “slash notation”, a “/” followed by the number of bits set to 1 in the subnet mask. For example, calculate the prefix length if the subnet mask is 255.255.128.0.

255.255.128.0   in binary 11111111.11111111.10000000. 00000000, now count the 1s from the left side, which is 17, so the prefix length is /17. We can easily calculate the subnet mask from prefix length.  For example, if the prefix length is /20, the total number of 1s in the subnet mask is 20. So write 1 twenty times followed by twelve 0s, 11111111.11111111.11110000. 00000000. Now convert the binary number into a decimal dotted notation, which is 255.255.240.0. We can manage a table for all possible prefixes.

The table below illustrates all possible prefixes for 32-bit addresses, including their subnet mask, both in binary and decimal. The first column lists all possible prefixes. The second column displays the binary value of the prefix, and the last column displays the resulting subnet mask.

Prefix-lengthBinary value for the prefix-lengthThe Subnet Mask
/811111111.00000000.00000000.00000000255.0.0.0
/911111111.10000000.00000000.00000000255.128.0.0
/1011111111.11000000.00000000.00000000255.192.0.0
/1111111111.1110000.00000000.00000000255.224.0.0
/1211111111.11110000.00000000.00000000255.240.0.0
/1311111111.11111000.00000000.00000000255.248.0.0
/1411111111.11111100.00000000.00000000255.252.0.0
/1511111111.11111110.00000000.00000000255.254.0.0
/1611111111.11111111.00000000.00000000255.255.0.0
/1711111111.11111111.10000000.00000000255.255.128.0
/1811111111.11111111.11000000.00000000255.255.192.0
/1911111111.11111111.11100000.00000000255.255.224.0
/2011111111.11111111.11110000.00000000255.255.240.0
/2111111111.11111111.11111000.00000000255.255.248.0
/2211111111.11111111.11111100.00000000255.255.252.0
/2311111111.11111111.11111110.00000000255.255.254.0
/2411111111.11111111.11111111.00000000255.255.255.0
/2511111111.11111111.11111111.00000000255.255.255.128
/2611111111.11111111.11111111.11000000255.255.255.192
/2711111111.11111111.11111111.11100000255.255.255.224
/2811111111.11111111.11111111.11110000255.255.255.240
/2911111111.11111111.11111111.11111000255.255.255.248
/3011111111.11111111.11111111.11111100255.255.255.252

Network Address

A network address is the first logical address of the network that uniquely identifies a network or a subnet. An IP address combines two separate addresses: the network address and the host address. But if we eliminate the host address from the IP address, the remaining address will be the network address. In other words, a network address is an IP address without a host address or an IP address in which all host bits are turned 0s.

We can find the network address applying the logical AND process between the binary representation of the IP address and subnet mask. Align the bits in both addresses, and perform a logical AND on each pair of the respective bits. Then convert the individual octets of the result back to decimal. For example, if we have a host IP address 172.100.20.50 and the subnet mask is 255.255.128.0 calculate the network address for the IP address. The figure below illustrates the solution to the above example.

prefix

Broadcast Address

The broadcast address is the last logical address in the network or a subnet, and it is used to address all the nodes in the network simultaneously. This is a unique address that communicates with all hosts in a network. For example, when a host sends a packet to the network broadcast address, all hosts in the network will receive the packet. The broadcast address uses the highest address in the network range. The broadcast address has all 1s in the host portion. For example, find the broadcast address if the IP address is 172.100.20.0 and the subnet mask is 255.255.128.0. The figure below illustrates the solution to the above example.

broadcast

Host Address

The host address uniquely identifies the host in the network. The host portion always contains various 0s and 1s but never all 0s or all 1s.

First Host Address

The network’s first available host IP address has all 0s and ends with a 1 in the host portion. It is also called the first usable IP address.

Example

 Dotted Decimal NotationBinary
Network IP Address172.100.0.0/1710101100.01100100.00000000.00000000
First Usable IP address172.100.0.110101100.01100100.00000000.00000001

Last Host Address

The last available host IP address in that network which has 1s and ends with a 0 in the host portion. It is also called the last usable IP address.

Example

 Dotted Decimal NotationBinary
Last Usable IP Address172.100.127.25410101100.01100100.01111111.11111110
Broadcast IP Address172.16.127.25510101100.01100100.01111111.11111111
Network and Host Portion of IPv4 Address

Network and Host Portion of IPv4 Address

/ /

A unique network number is necessary for each network, and each host must require a unique IP address. The IPv4 address is a 32-bit number that uniquely identifies a network number and host. We generally express an IPv4 address in dotted decimal notation as four 8-bit fields separated by periods. Each 8-bit field represents 1 byte of the IPv4 address. The binary notation is very important to understand IP addresses and their portions. The IPv4 address consists of a network portion and a host portion.

The 32-bit stream of IPv4 addresses is significant for determining the network and host portions. Within the 32-bit stream, a number of bits identify the network portion, and a number of bits identify the host portion. The bits in the network portion must be the same for all devices in the same network.

The bits within the address’s host portion must be unique to identify a specific host within a network. If two hosts have the same bit pattern in the specified network portion of the 32-bit stream, those two hosts will be located in the same network. We can identify the host and network portions of the IP address using a subnet mask. Each host in the network has three essential parameters in a network:-

Host Unique IPv4 address.

Each host required a unique IPv4 address to identify the network’s host number.

Host Default gateway

The host default gateway is used to identify the local gateway to reach other networks. Generally, the router interface IP address works as the default gateway.

Subnet Mask

A subnet mask is a 32-bit stream that defines a range of available IP addresses within a network. It is used to subdivide large networks into more minor subnetworks. Hosts within the same subnet mask can communicate directly with each other, while systems on different subnet masks must communicate through a router. The size of a subnet depends on the requirements and the network technology employed. A point-to-point subnet allows only two devices to connect, while a data centre subnet requires more. A subnet mask is also known as an address mask.

Understanding the subnet mask is very important to find out the network portion and host portion of the IP address. The network address represents all the devices on the same network. The figure below illustrates the dotted decimal address with a subnet mask. The network bits in the subnet mask must be 1s, and the host bits in the subnet mask must be 0s.

Network and Host Portion with Subnet Mask

The figure below illustrates the network and host portion, including the subnet mask. It is a sequence of 1 bits followed by 0 bits. It identifies the network and host portions of an IPv4 address uniquely. We can compare the subnet mask to the IPv4 address bit, from left to right, as shown in the figure. The 1s in the subnet mask identify the network portion, while the 0s in the subnet mask identify the host portion. ANDing is the process that determines the network portion and host portion.

Host Portion

ANDing

When a source host attempts to communicate with a destination host, it uses its subnet mask to determine whether the destination host is on the local network or a remote network. Before creating an IPv4 packet, the destination network address must be extracted from the destination address. This is done using logic called ANDing.

ANDing is the essential binary operation used to determine the network address. Two other processes are also used in data networking but not for determining IP addresses. The other two are OR and NOT operation. The IPv4 address is logically ANDed with its subnet mask to determine the associated network address. When ANDing between the address and the subnet mask is performed, the result gives the network address.

AND Operation

The source and destination IP addresses are compared to the source’s subnet mask by applying the ANDing process. An AND result is created for both source and destination addresses. The hosts are on the same network if the result is the same. The destination host is on a remote network if the result is different. All traffic destined for that remote host should be directed to the default gateway. The logical AND operation of two bits gives the following result.

1 AND 1 = 1

1 AND 0 = 0

0 AND 1 = 0

0 AND 0 = 0

So, to identify the network address of an IPv4 host, the IPv4 address is logically ANDed, bit by bit, with the subnet mask. ANDing between the address and the subnet mask produces the network address. So anything ANDed with a 0 produces a 0.

As we learned previously, all bits of the subnet mask that represent the host are 0s, so the host portion of the resultant network becomes all 0s. Remember that all 0s in the host portion of an IPv4 address mean that this is the network address. As we know, all bits of the subnet mask in the network portion are all 1s. When each of these 1s is ANDed with a parallel bit of the address, the resulting bits are identical to the original address bits.

Example 1: Find out the network ID for the following IP address.

Positional Number System and Examples

Positional Number System and Examples

/ /

In a positional number system, each symbol represents a different value depending on the position it occupies in a number, and each system has a value that relates to the number directly next to it. The total value of a positional number is the total of the resultant value of all positions. The decimal number system is known as a positional number system because the value of the number depends on the position of the digits. For example, 12345 has a very different value than 54321, although the same digits are used in both numbers. The position in which the digit appears affects the value of that digit.

In a positional number system, the value of each digit is

determined by which place it appears in the total number. The lowest place value is the rightmost position, and each successive position to the left has a higher place value. So, the rightmost position represents the “ones” column, the next position represents the “tens” column, the next position represents “hundreds,” and the next position represents the “thousand” and then ten thousand, etc. Therefore, the number 54321 represents 5x ten thousand, 4x one thousand, 3x hundred, 2 tens and 1 x one, whereas the number 12345 represents 1x ten thousand, 2 x one thousand 3 hundred, 4 x tens and 5 ones.  The binary, octal and hexadecimal are all examples of a Positional Number System. 

Decimal Positional Notation

The decimal positional notation system works as described in the table in the figure below. To use the positional number system, match a given number to its positional value. The arrow at the left shows that the table can be expanded according to position and can be calculated.

positional number system

Radix

The Term Radix describes the number of digits utilized in the positional number system or to identify the system’s base. The decimal notation system is based on 10, so the radix is 10.

Position in

It shows the position of the decimal number. The position starts from the right and moves to the left. So 0 is the 1st position 1 is the 2nd position, 2 is the 3rd position and so on. The numbers also represent the exponential value that will be used to calculate the positional value of the 4th row.

Calculate

The third row calculates the positional value by taking the radix and raising it by the exponential value of its position. Importantly, n0 is always = 1.

Position Value

The first row shows the number base or radix. From left to right, the values listed represent units of thousands, hundreds, tens, and ones.

Example – 12345 and 54321

Positional Number System

Binary Positional Notation

The binary positional notation also operates similarly to the decimal number system, as shown in the figure below. It also has a Radix, Position, which is from right to left; Calculation and positional value as described for decimal. The Radix for Binary is 2. The example is also shown below

Positional Number System

Examples

binary to decimal converstion

Converting Between Decimal and Binary

Converting binary to decimal (base-2 to base-10) numbers and back is an essential concept for understanding the binary numbering system. Binary number systems form the basis for all computers, digital systems, and programming languages, and they are also essential for comprehending IP address and IP address subnetting.

Binary to Decimal Conversion

To understand IP addressing and subnetting, the network technician must understand how to convert from binary to decimal. There are several ways to convert from binary to decimal. Here, we will realize conversion from binary to decimal and then from decimal to binary.

Binary to Decimal Using Positional Notation

Positional notation is one of the most used methods for converting binary and decimal, so if we have a binary number 110001102 and want to convert this number to decimal base 10 system using the positional system notation.

The figure below illustrates the conversion of the binary to decimal. Write down the positional value from right to left and right down the binary number in the next row below the positional values. Next, multiply the binary numbers in the second row with their corresponding positional value in the first row and add them up to get the decimal number, 199.

binary to decimal converstion

The positional value doubles from right to left. For example, from right to left, the first positional value is 1, the next position value is 2, double 1 (the first position value), and the third place value is 4, double the second position value. We can write positional values using this method according to the binary digits.

The following binary value is 10111100. So,  write the positional value according to the number of digits in the binary value. Then, write the binary numbers below the positional values and map them up. If the digit is a 1, write its corresponding positional value below the line, under the digit. If the digit is a 0, write a 0 below the line, under the digit and add up the numbers written below the line. This is the decimal equivalent of the binary number. See figure the figure below.

binary to decimal converstion

Now that we understand the basic conversion from binary to decimal, we can try to convert a binary IPv4 address to its dotted-decimal equal. First, divide 32 bits of the IPv4 address into four 8-bit octets. Then, calculate the binary positional value of the first octet binary number and all others.

For example, consider that 11110110.10111111.11101011.11011011 is the binary IPv4 address. As shown in the Figure below, you must convert the binary address to decimal, starting from the first octet. Enter the 8-bit binary number under the positional value of row 1 and then calculate to produce the decimal number for the first octet of the dotted decimal notation. Next, convert the remaining octets. Write down the full IP address using dotted decimal notation.

binary IP to doted decimal notation

 Decimal to Binary Conversion

Decimal to binary conversion is also essential to understand; we can convert a dotted decimal IPv4 address to binary. We can also use a positional value table to convert from decimal to binary. The figure below illustrates the decimal to the binary conversion process. For example, we want to convert Figure 246 into binary. The steps for converting from decimal to binary are the following:

decimal to binary conversion

Step-1

Write down the positional value from left to right, as shown in the figure below. If the decimal number (242 in our case) is equal to or greater than the most significant bit (128), add a binary 1 below the 128 positional value and subtract 128 from the decimal number (242 -128 =114 in our case). If not, enter binary 0 below the 128 positional value.

Step-2

Compare if the remainder (114) equals or exceeds the next most significant bit (64). If yes, add a binary 1 below the 64 positional value and subtract the positional value 64 from the decimal number (114 -64 =50  in our case). If no, then enter binary 0 below the 64 positional value.

Step-3

Compare if the remainder (50) equals or exceeds the next most significant bit (32). If yes, add a binary 1 below the 32 positional value and subtract the positional value 32 from the decimal number (50 -32 =18  in our case). If no, then enter binary 0 below the 64 positional value.

Step-4

Compare if the remainder (18) equals or exceeds the next most significant bit (16). If yes, add a binary 1 below the 16 positional value and subtract the positional value 16 from the decimal number (18 -16 =2  in our case). If no, then enter binary 0 below the 16 positional value.

Step-5

Compare the reminder (2) with the following -most significant bit, you can see that the remainder is less than the considerable value (80), so add a binary 0 in the 8 positional value and step forward to the next positional value, which is (4), the remainder is also less than this positional value, so, add 0 below this position value and step forward to next value. The next value is positional value is (2), So, Subtract the reminder 2 from the positional value (2-2=0), put the 0 in the last position.

IP address Classes- Exclusive Explanation

IP address Classes- Exclusive Explanation

/ /

The IP address is an identifying number for network devices. It is similar to a home or business address supplying that specific physical location with a particular address—devices on a network differentiated from one another through IP addresses.

An IP address allows a device to communicate with other devices over an IP-based network, like the Internet. There are two primary standards for IP addresses: IPv4 and IPv6. In this article, I will discuss the IPv4 address. The IPv6 address will be discussed in later articles.

IPv4 Addressing

IPv4 is the fourth revision of IP and a widely used protocol for data communication over various networks. It is defined and specified in IETF publication RCF 791. A connectionless protocol provides logical connections between network devices and unique identification for each device.

Depending on the network type, we can configure the IPv4 addresses on the network devices manually or automatically. IPv4 uses 32-bit addresses for Ethernet communication in five IP address classes: A, B, C, D, and E.

Address Architecture

TCP/IP was introduced in the 1980s. At that time, the Internet used a two-level addressing scheme, which offered sufficient scalability. The 32-bit-long IPv4 address identifies a network and a host number, with 16 bits reserved for the network and 16 for host identification. The figure below illustrates the 32-bit address architecture in the 1980s.

The current IPv4 address is also 32-bit long and contains two portions: a network and host portions. The network portion identifies the host’s network, and the host portion shows the number of the host in the network. The host portion identifies the device or the host. The router uses the network portion of the IP addresses to make routing decisions and to facilitate communication between hosts that belong to different networks. Like routers and computers, humans can’t work with strings of 32 bits (1s and 0s).

Therefore, we express the 32-bit IP address in dotted-decimal notation, as we know that 32-bit addresses are further divided into four groups of eight, called octets. An octet ranges from 000000000 to 11111111. Each octet is converted to decimal and separated by decimal points or dots. The range of each octet in decimal is from 0 to 255.

For example, 10.10.10.1, 172.16.16.254 and 192.168.0.254 are IP addresses expressed in dotted decimal notations. If we can convert these addresses to binary. For example, the binary of the above addresses is 00001010. 00001010. 00001010.00000001, 10101100. 00010000.00010000. 11111110, 11000000. 10101000.00000000.11111110.

IP Address Classes

At the start of TCP/IP, the IP address classes define the network and host portions. IPv4 addresses are divided into five different IP address classes. The first few bits of the first octet determine the IP address class. These bits are known as high-order bits (HOB). Although the IP address classes can still be applied to IP addresses, networks today often ignore the class rules in favor of a classless IP scheme. The five IP address classes are A, B, C, D, and E.

Classes A, B, and C have different bit lengths for addressing the network host. Class D addresses are reserved for multicasting, while Class E addresses are reserved for future use. Depending on the address class, each of the four octets of an IP address represents the network portion of the host portion. The figure below illustrates the network and host portions of the respective Class A, B, C, and D addresses.

IP address Classes

The first three IP address classes, A, B, and C, host addresses in any IP network. However, the Class D addresses are used for multicasting. Class E addresses are reserved for experiments in labs and medical equipment and are not shown in the above figure.

It is not easy to identify the network and host portions of any dotted-decimal IP address because IP addresses are not actually four numbers. They contain 32 different numbers or 32 bits (0 or 1s). The figure below illustrates all the important figures of IP address classes.

IP address Classes

Class A

The most significant bit of the class A network is 0, also known as the high-order bit(HOB). The remaining seven bits in the first octet define the number of networks in class A addresses, and the three octets (24 bits) define the total number of IP addresses available in the class. The figure below illustrates Class A’s address bit distribution.

If the first bit of an IP address’s first octet is binary 0, the address is a Class A address. With the first bit being 0, the lowest number is 00000000 (decimal 0), and the highest number is 01111111 (decimal 127). Any address that starts with a value between 0 and 127 in the first octet is a Class A address. The numbers 0 and 127 are reserved and cannot be used as a network address.

Class A network can accommodate a very large number of hosts because only the first octet is reserved for the network number. The three octets, or 24 bits, are reserved for the host portion of the network. Each network of this class supports a maximum of 16,777,214 (2 24 -2) hosts per network. Figure two is subtracted because the first and last addresses are reserved as network IDs and broadcast IPs. The lowest address is 24, 0s in the host portion, and the highest is 24, 1s in the host portion.

The routing table uses network ID for the routing table. So, an address with all 0s in the host portion cannot be used with the individual host. For example, 10.0.0.0 is a Class A Address containing all 0s in the host portion. So it is network identification and cannot be configured on network hosts and devices.

Every network also requires a broadcast address, which can be used to send a message to each host on the network. This address has all 1s on the host portion. For example, a broadcast address for network 10.0.0.0 would be 10.255.255.255.

The total number of networks in Class A is 126. Each of the 126 Class A networks has almost 17 million host addresses, which make up 50 % of the entire IPv4 address space. The 0.0.0.0 address is also reserved for the default route. 127.0.0.0 is reserved for the local loopback address, which is why the Class A network range is from 1 to 126, and Class B addresses start from the address of 128.0.0.0.

A Class A network provides many possibilities for any organization or company. It is a huge global network with many hosts, and the hosts in such a network do not function as members of the same logical group.

Class A addresses creating a large broadcast domain, but network administrators need smaller logical groupings to control broadcasts, apply policies, and troubleshoot problems. This is possible by applying a subnet mask, which allows subnetting.

Subnetting breaks a large block of addresses into smaller groups called subnetworks. It avoids the waste of IP addresses and is also helpful for better efficiency. The default subnet mask for a class A IP address is 255.0.0.0. The private IP address range for class A is 10.0.0.0 to 10.255.255.255.

Class B

The high-order bit of class B addresses starts with a binary 10 in the first 2 bits of the first octet. So, the lowest number of class B addresses is 10000000 (decimal 128), and the highest is 10111111 (decimal 191). So, any IP address starts with a range between 128 – 191, and the first octet is a class B IP address. Class B network can provide addressing scheme to medium-size networks.

In Class B, the first two octets represent the network, and the other two represent the address’s host portion. So class B has 16384 (214) Network addresses and 65534 (216-2) Host addresses. So, each Class B network can support up to 65,534 hosts. The Class B network is much smaller than the networks of Class A. Just like Class A networks, we can subnet the Class B network to improve network efficiency. The figure below illustrates the 32-bit distribution of the Class B network.

The first octet of a Class B address has 64 possibilities ranging from 128 to 191. The second octet has 256 possibilities ranging from 0 to 255. That gives 16,384 networks. We can multiply 64 by 256 to get the total possible network in Class B. The default subnet mask for Class B IP addresses is 255.255.0.0. Class B addresses also have a private IP address range from 172.16.0.0 to 172.31.255.255.

Class C

The high-order bits of class C address are binary 110. So, the lowest number that starts with binary 110 is 11000000 (Decimal 192), and the highest number that begins with binary 110 is 11011111 (Decimal 223). So, the class C range is from 192 to 223 in the first octet.

Class C addresses were initially planned for a small network. The first three octets of a Class C address represent the network portion of the IP address, and the fourth octet represents the host portion. The figure below illustrates the distribution of Class C address bits.

As we learn, the first 3 bits of a Class C address are always 110, So 21 bits are left in the network portion of the address, which results in 221 or 2,097,152 Class C networks. Each network contains 254 (28 -2) hosts each. The first and last addresses are reserved for network identification and broadcasting. The default subnet mask for class C IP addresses is 255.255.255.0. Class C addresses are also a private IP address range starting from 192.168.0.0 to 192.168.255.255

Class D

The high-order bit of a Class D address is 1110 in the first octet. So, the lowest number starting with 1110 is binary 11100000 (Decimal 224), and the highest is 11101111 (Decimal 239). So, the range of Class D addresses is 224 to 239 in the first octet. Class D addresses are not used with individual hosts; they can be used with hosts called a host group or multicast group.

It is used when a single message requires sending to many selected recipients, known as multicast or multicasting. Multicast is different from broadcast. Every device on a logical network must process a broadcast, whereas only devices configured to listen for a Class D address receive a multicast.

Class E

The high-order bits of a class E IP address begin with 1111. The range of this class starts with 11110000 (decimal 240) and ends with 11111111 (decimal 255). So, the range of class E is from 240 to 255 in the first octet. Class E addresses are reserved for experimental purposes.

Interface configuration

Cisco Router Interface Configuration

/ /

A physical connection is necessary for the router’s Ethernet interface configuration. However, when establishing a connection, you can proceed with the basic interface configuration of Ethernet, Fast Ethernet, or Gigabit Ethernet. After connecting to a router, you need to get into the Global Configuration Mode of your router using the following commands:

Interface configuration

The next option is to choose the correct interface. Many different types of interfaces are available on Cisco routers, such as Ethernet, Fast Ethernet, Gigabit Ethernet, and serial interface. All interfaces in IOS are exactly numbered. For example, we want to configure Fast Ethernet, which has a number of 0/0. We should enter the command as shown below.

Router(config)#interface FastEthernet 0/0

Adding a Description to the Ethernet Interface

This feature is not necessary, so you may bypass it. This feature provides a description of the interface, and it does not assist with the configuration. So, it just helps prevent human error.

Router(config-if)#description <Write description of the interface here>

Setting IP Address on Interface

Now you have done everything necessary to add the IP address to the interface. Use the following command to enter an IP address according to your IP scheme to the interface.

Router(config-if)#ip address 192.168.100.1 255.255.255.0

Enabling Interface

Before using the router interface, you also need to enable the corresponding interface. We can enable the router interface by entering the following command.

Router(config-if)#no shutdown
%LINK-5-CHANGED: Interface FastEthernet0/0, changed state to up

Verifying Router Interface Configuration

We can verify interface configuration using several commands. For example, the <show ip interface brief> is the most helpful command for verifying interface configuration. The output of this command displays all interfaces with their IPv4 address and the current status. The configured and connected interfaces should display a status “up” and Protocol “up”. Any other statements would indicate a problem with the configuration or the cabling. Also, remember that show commands are working in “Privileged mode”

In the same way, we can verify the configuration of the interface using <show running-config>  and also with show startup-config. We can also verify connectivity from the interface using the ping command. The ping command sends five consecutive pings and measures minimal, average, and maximum round-trip times. Exclamation marks in Cisco routers also verify connectivity.

Following is the output of the show ip interface brief command, which shows all three router interfaces. FastEthernet  0/0, status is up, and protocol is also up. This interface is connected to other networks, and the protocol is up. FastEthernet status is up, it means that interface is configured and enabled with no shutdown command, its protocol is down, it’s mean that there is something wrong with the cable or some problem from another side. Serial 0/0/0 interface is not configured, not enabled and there is also no IP address assigned to this interface.

Following are other commands that we can use to verify interface configuration.

  • show interfaces– Displays statistics for all interfaces on the device.
  • Ping – Using the ping command, we can generate five exclamation marks verifying connectivity to the remote side.
  • show running-config-.The command shows the entire configuration of the router.
  • show startup-config:- When the configuration is saved with the write command, we can verify it using the command mentioned.

Load More