Network Devices

The Domain Name System is a hierarchical distributed naming system for computers, services, or any resource connected to internet or a private network. It associates various information with domain names assigned to each of the participating entities. Most prominently, it translates easily memorized domain name to the numerical IP addresses needs for the purpose of locating computer services and devices worldwide. By providing a worldwide, distributed keyword-based redirection service, the Domain Name System is an essential component of the functionality of the internet.

An often-used analogy to explain the Domain Name System is that it serves as the phone book for the internet by translating human-friendly computer hostnames into IP addresses. For example the domain name www.example.com translates to the addresses 192.163.0.10 (IPv4) and 2001:500:88:200::10 (IPv6). Unlike a phonebook the DNS can be quick updated, allowing a service's location on the network to change without effecting the end users, who continue to use the same hostname. Users take advantage of this when they use meaningful uniform resource locator (URL) and E-mail addresses without having to known how the computer actually locates the services.

The Domain Name System distributes the responsibility of assigning domain names and mapping those names to IP addresses by designating authoritative name serves for each domain. Authoritative name servers are assigned to be responsible for their particular domain and in turn can assign other authoritative name servers for their sub-domains. This mechanism has made the DNS distributed and fault tolerant and has held avoid the need for a single central register to be continually consulted and updated. Additionally the responsibility for maintaining and updating the master record for the domain is spread among many domain name registers, who compete for the end-user's (the domain-owner's) business. Domain can be moved from one registrar to other registrar at any time.

The Domain Name System also specifies the technical functionality of this data base service. It defines the DNS protocol, a detailed specification of the data structures and data communication exchanges used in DNS, as part of the internet protocol suit.

Protocols

A communication protocol is (Networking protocol) is a system of digital message formats and rules for exchanging messages in or between computing system and in telecommunications. A protocol may have a formal description. Protocol may include signaling, authentication and error detection and correction capability.

In a routing protocol, it specifies that how routers communicate with each other and with the other types of machines. Protocols are determines and enable the routes between the nodes on a computer network. Algorithms determine the specific choice of routing. A router has knowledge only the direct attached networks and a protocol shares information about the neighbors immediate and then throughout the network. A router can understand the network topology through the protocol. So we can say that a protocol is playing very important role in a network. Although, there are many types of protocols.

Types of protocols

There are many types of protocols for different purpose in networking.

Routing protocols

IS-IS, OSPF, IGRP and EIGRP, RIP, BGP,

Internet protocols

Application Layer

DHCP, DHCPv6, DNS, FTP, HTTP, IMAP, IRC, LDAP, MGCP, NNTP, BGP, NTP, POP, RPC, RTP, RTSP, RIP, SIP, SMTP, SNMP, SOCKS, SSH, Telnet, TLS/SSL, XMPP.

Transport Layer

 TCP, UDP, DCCP, SCTP, RSVP, TP-TCP, NC, MTP

Network Layer

IP(IPv4,IPv6), ICMP, ICMPv6, ECN, IGMP, IPSec, GGP.

Link Layer

A network mask is used when a network is not sub netted. The subnet mask is used to find the first address in the block. However when a mask is sub netted, the situation is different. We must have a subnet mask. The subnet has more 1s.

Subnetting increases the length of the netid and decrease the length of hostid. When we divide a network to s number of subnetworks, each of number of hosts, we can calculate the subnetid for each subnetwork as in which n is the length of netid,.

When a network is subnetted, the first address in the subnet is the identifier of the subnet and is used by the router to route the packets destined for that subnet works. Given any address in the subnet, the router can find the subnet mask using the same procedure we discussed to find the subnetwork mask. ANDing the given address with the subnet mask.

Subnetting couldn’t completely solve address depletion problems in classful addreeing, because most organization did not want to share their granted blocks with others. since class C blocks were still available but the size of block did not meet the requirement of new organization that wanted to join the internet, one solution was super netting . in super netting, an organization can combine several class C block to create a larger range of addresses. In other, words several networks are combined to create a supernet work. By doing this, an organizarion can apply for several class C blocks instead of just one. For example, an organization that needs 1000 addresses can be granted four class C blocks.

In subnetting, a network divides into several smaller networks with each subnetwork  having its own subnetworks. A portion of IP address is indicating the network (netid), and a portion indicates the network hostid. This means that there is a sense of hierarchy in IP addressing. To each a host on the internet, we must first reach the network using the first portion of the address. Then we must reach the host itself using the second portion. In the other word, IP address is designed with two level of hierarchy. However in many cases two levels of hierarchy are not enough. For example, imagine an organization with the network address 141.14.0.0 (a class B address). The organization has two hierarchical addressing, but cannot have more than one physical network. One solution of this problem is subnetting. Further division of a network into smaller networks is called subnetting.

Three level of hierarchy

Adding subnetworks an intermediate level of hierarchy in the IP addressing system. Now we have three levels; site, subnet and host. The site is the first level. The second level is subnet and the tird level is host of hierarchy, it defines the connection of the host to the subnetwork.

Mask

If the network address is given, we can find the block and the range of addresses in the block.  What about the reserves? If an address is given, can we find the given address (the beginning address in the block). This is important because to route a packet to the correct network, a router needs to extract a network address from the destination address (a host address) in the packet header.

One way we can find the network address to first find the class of the address and the net ID. We then set the host ID to zero to find the network address. For example, if the address is 134.45.78.2 is given, we can immediately say that the address belong to class B. the net ID is 134.45 (2 bytes)  and the network address is 134.45.0.0.

The above method is feasible if we not subnetted the network; that is, if we have not divided the network into subnetworks. A general procedure that can be used involves a mask to find the network address from a given address.

A mask is a 32 bits binary number that gives first address in the block (the network address). When bit-wise ANDed with an address in the block.

AND Operation

Masking uses the bit-wise AND operation defined in computer science. The operation is applied bit by bit to the address and the mask.

One problem with the classfull addressing is that each class is dividing into a fixed number of blocks with each block having the fixed size. Let’s look

Class A

Class A is divided into 128 blocks with each block having a different net id. First block covers address from 0.0.0.0 to 0.255.255.255 (net id 0). The second block covers address 1.0.0.0 to 1.255.255.255 (net id 1). The last block covers address form 127.0.0.0 to 127.255.255.255 (net id 127).

Note: each block of addresses the first byte (net id) is the same, but the other three bytes (host id) can take any value in the given range.

The first and last block in this are reserved for special purpose as we will discuss shortly. In addition one block is used for private address. The remaining 125 blocks can be assigned to organization. This means that the total number of organization that can have class A address is only 125. However, each block in this class contains 16,777,216 addresses. This address is called network address. It defines the network of the organization, not individual hosts. The organization is not allowed to use last address; it is reserved for a special purpose. Class A address is design for large organization with a large number of hosts or routers attached t their network.

Class B

Class B is divided into 16,384 blocks with each block having a different net id. Sixteen blocks are reserved for private addresses, leaving it 16,368 blocks for assignment to organization. The first block covers address form 128.0.0.0 to 128.0.255.255 (net id 128.0). the last block covers address from 191.255.0.0 to 191.255.255.255 (net id 191.255).

Note: each block of address the first 2 bytes net ID are same but other 2 bytes are host ID can take any value in the given range.

There are 16,368 blocks that can be assigned. This means that the total number of organization that can have class B address is 16,368. However, each block in this class contain 65,536 addresses, the organization should be large enough to use all of these addresses.

Class B was designed for mid size organization that many have tens of thousands of hosts or routers attached to their network. However, the number of addresses in each block 65,536 is larger than the needs of most midsize organizations.

Class C

Class C is divided into 2097152 blocks with each block having a net ID. 256 blocks are used for private addresses, leaving 2,096,896 blocks for assignment to organization. The first block covers address from 192.0.0.0 to 192.0.0.255 (net id 192.0.0). the last address covers address from 223.255.255.0 to 223.255.255.255 (net id 223.255.255).

Note: the each block of address the first 3 bytes are the same but last one byte can take any value in the given range. There are 2096902 blocks that can be assigned have a class C address is 2096902. However, each block in this class contains 256 addresses, which means the organization should be small enough to need less than 256 addresses.

Class C was designed for small size organization with a small number of hosts or routers attached to their network.

Class D

There just one block of class D addresses. It designed for multicasting. Each address in this class is used to define one group of hosts on the internet. When a group is assigned an address in this class, every host that is member of this group will have a multicast address in addition to its normal (unicast) address.

Class E

There is just one block also in class E address. It was designed for used as reserved address. The last address in this class 255.255.255.255 is used for a special address.

Network Addresses

Network addresses play a very important role in classfull addressing. A classful address has several properties:

We try to understand with the example:

Given the network address 132.210.0.0, class is B  because the first byte is between the 128 to 191. The block has net id of 132.21, the address range from 132.21.0.0 to 132.21.255.255.

IP addressing, when started a few decades ago, used the concept of classes. This architecture is called class full IP addressing. In the mid of 1990s, a new architecture, Called classless IP addressing was introduced that will eventually supersede the original architecture. However, most of the internet is still using calssfull addressing and the migration is slow. To understand the classfull IP addressing it is important to understand classless addressing.

In classfull IP addressing, the IP address is divided into five classes A,B,C,D and E. each class is occupies some part of the whole address space, see below the table mansion the class occupation of the address space (approximate).

We can see that the class A covers the half of the address space, a serious design flow. Class B cover ¼ of the whole address space, another design flow. Class C is cover the 1/8 of the address, and class D and E each cover the 1/16 of the address space.

We can find the class of an address when the address is given in binary notation or in dotted decimal notation.

Find the class in binary notation

If the address is given in binary notation, the first bits can immediately tell us the class of the address.

Find the class in dotted decimal notation

When the address is given in dotted decimal notation, then we need to look only at the first byte to determining the class of the address. Each class has a specific range of number.

Net ID and Host ID

In classfull addressing an IP in classes A,B and C is divided into net id and host id.

Note: Class D and E are not divided into net id and host id.