System and Network Administration

System and Network Administration – System administration is a job done by IT experts for an organization. The job is to ensure that computer systems and all related services are working well.

What is TCP/IP?

Introduction of TCP/IP model

TCP/IP is a set of network protocols (Protocol Suite) that enable communication between computers. Network protocols are rules or standards that govern network communications.

If two devices in a network need to communicate together, they need to use common set of network protocols. This can be compared with how humans speak. A French person cannot communicate with a Vietnamese person (without help from a translator) since they speak different languages.

You can select from different network protocols to use in your network, but TCP/IP is the industry standard. Almost all Operating Systems now support TCP/IP. Internet is working on TCP/IP. TCP/IP is known as “the language of the Internet”.

If you want your computer and computer like devices (laptops, tablets, mobiles etc.) to work on the Internet, you have to use TCP/IP protocol suite.

Features of TCP/IP

Computing industry is using TCP/IP protocol suite for last five decades. TCP/IP protocol suite is a tested, proved and robust protocol suite.

Multi Vendor support – TCP/IP is implemented by many hardware and software vendors. It is an industry standard and not limited to any specific vendor.
Interoperability – Today we can work in a heterogeneous network (consisting of devices, Operating Systems, software from different vendors) because of TCP/IP. A network user who is using a Windows Operating System based computer can download files from a Linux machine, because both Operating Systems support TCP/IP. TCP/IP eliminates the cross- platform/multi-vendor boundaries.
Logical Addressing. Every network adapter has a globally unique and permanent physical address, which is known as MAC address (physical address or hardware address).

The physical address is burnt into the card while manufacturing. Low-lying hardware-conscious protocols on a LAN deliver data packets using the adapter’s physical The network adapter of each computer listens to every transmission on the local network to determine whether a message is addressed to its own physical address.

For a small LAN, this will work well. But when your computer is connected to a big network like internet, it may need to listen to millions of transmissions per second. This may cause your network connection to stop functioning.

To avoid this, network administrators often segment (divide) big networks into smaller networks using devices such as routers to reduce network traffic, so that the unwanted data traffic from one network may not create problem in another network.

A network can be again subdivided into smaller subnets so that a message can travel efficiently from its source to the destination. TCP/IP has a robust subnetting capability achieved using logical addressing. A logical address is an address configured through the network software. The logical addressing system used in TCP/IP protocol suite is known as IP address.

A router is a network infrastructure device which can read logical addressing information and direct data across the network to its destination. TCP/IP is a routable protocol, which means the TCP/IP data packets can be moved from one network segment to another.
Name Resolution. IP addresses are designed for the computers and it is difficult for humans to remember many IP addresses. TCP/IP allows us to use human-friendly names, which are very easy to remember. Name Resolutions servers (DNS Servers) are used to resolve a human readable name (also known as Fully Qualified Domain Names (FQDN)) to an IP address and vice versa.

Error Control and Flow Control. The TCP/IP protocol has features that ensure the reliable delivery of data from source computer to the destination computer. TCP (Transmission Control Protocol) defines many of these error- checking, flow-control, and acknowledgement
Multiplexing/De-multiplexing. Multiplexing means accepting data from different applications and directing that data to different applications listening on different receiving computers. On the receiving side the data need to be directed to the correct application, for that data was meant for. This is called De-multiplexing. We can run many network applications on the same computer, by using logical channels called ports. TCP/IP provides means for delivering packets to the correct application based on port numbers. In TCP/IP, ports are identified by using TCP or UDP port

TCP/IP model

The TCP/IP model was developed prior to the OSI

The TCP/IP model is not exactly similar to the OSI
The TCP/IP model consists of five layers: the application layer, transport layer, network layer, data link layer and physical
The first four layers provide physical standards, network interface, internetworking, and transport functions that correspond to the first four layers of the OSI model and these four layers are represented in TCP/IP model by a single layer called the application
TCP/IP is a hierarchical protocol made up of interactive modules, and each of them provides specific

Here, hierarchical means that each upper-layer protocol is supported by two or more lower-level protocols.

Functions of TCP/IP layers:

Network Access Layer

A network layer is the lowest layer of the TCP/IP
A network layer is the combination of the Physical layer and Data Link layer defined in the OSI reference
It defines how the data should be sent physically through the
This layer is mainly responsible for the transmission of the data between two devices on the same
The functions carried out by this layer are encapsulating the IP data gram into frames transmitted by the network and mapping of IP addresses into physical
The protocols used by this layer are ethernet, token ring, FDDI, X.25, frame

Internet Layer

An internet layer is the second layer of the TCP/IP
An internet layer is also known as the network
The main responsibility of the internet layer is to send the packets from any network, and they arrive at the destination irrespective of the route they

Following are the protocols used in this layer are:

IP Protocol: IP protocol is used in this layer, and it is the most significant part of the entire TCP/IP suite.

Following are the responsibilities of this protocol:

IP Addressing: This protocol implements logical host addresses known as IP addresses. The IP addresses are used by the internet and higher layers to identify the device and to provide internet work
Host-to-host communication: It determines the path through which the data is to be
Data Encapsulation and Formatting: An IP protocol accepts the data from the transport layer protocol. An IP protocol ensures that the data is sent and received securely, it encapsulates the data into message known as IP
Fragmentation and Reassembly: The limit imposed on the size of the IP datagram by data link layer protocol is known as Maximum Transmission unit (MTU). If the size of IP datagram is greater than the MTU unit, then the IP protocol splits the datagram into smaller units so that they can travel over the local network. Fragmentation can be done by the sender or intermediate router. At the receiver side, all the fragments are reassembled to form an original
Routing: When IP datagram is sent over the same local network such as LAN, MAN, WAN, it is known as direct delivery. When source and destination are on the distant network, then the IP datagram is sent indirectly. This can be accomplished by routing the IP datagram through various devices such as

ARP Protocol

ARP stands for Address Resolution Protocol.
ARP is a network layer protocol which is used to find the physical address from the IP

· The two terms are mainly associated with the ARP Protocol:

ARP request: When a sender wants to know the physical address of the device, it broadcasts the ARP request to the
ARP reply: Every device attached to the network will accept the ARP request and process the request, but only recipient recognize the IP address and sends back its physical address in the form of ARP reply. The recipient adds the physical address both to its cache memory and to the datagram header

ICMP Protocol

ICMP stands for Internet Control Message Protocol.
It is a mechanism used by the hosts or routers to send notifications regarding datagram problems back to the
A datagram travels from router-to-router until it reaches its destination. If a router is unable to route the data because of some unusual conditions such as disabled links, a device is on fire or network congestion, then the ICMP protocol is used to inform the sender that the datagram is
An ICMP protocol mainly uses two terms:
- ICMP Test: ICMP Test is used to test whether the destination is reachable or
- ICMP Reply: ICMP Reply is used to check whether the destination device is responding or
The core responsibility of the ICMP protocol is to report the problems, not correct them. The responsibility of the correction lies with the sender.
ICMP can send the messages only to the source, but not to the intermediate routers because the IP datagram carries the addresses of the source and destination but not of the router that it is passed

Transport Layer

The transport layer is responsible for the reliability, flow control, and correction of data which is being sent over the network.

The two protocols used in the transport layer are User Datagram protocol and Transmission control protocol.

· User Datagram Protocol (UDP)

It provides connectionless service and end-to-end delivery of transmission.
It is an unreliable protocol as it discovers the errors but not specify the
User Datagram Protocol discovers the error, and ICMP protocol reports the error to the sender that user datagram has been damaged.
UDP consists of the following fields: Source port address: The source port address is the address of the application program that has created the message. Destination port address: The destination port address is the address of the application program that receives the message. Total length: It defines the total number of bytes of the user datagram in Checksum: The checksum is a 16-bit field used in error detection.
UDP does not specify which packet is lost. UDP contains only checksum; it does not contain any ID of a data

Transmission Control Protocol (TCP)

It provides a full transport layer services to
It creates a virtual circuit between the sender and receiver, and it is active for the duration of the
TCP is a reliable protocol as it detects the error and retransmits the damaged frames. Therefore, it ensures all the segments must be received and acknowledged before the transmission is considered to be completed and a virtual circuit is
At the sending end, TCP divides the whole message into smaller units known as segment, and each segment contains a sequence number which is required for reordering the frames to form an original
At the receiving end, TCP collects all the segments and reorders them based on sequence

Application Layer

An application layer is the topmost layer in the TCP/IP
It is responsible for handling high-level protocols, issues of
This layer allows the user to interact with the
When one application layer protocol wants to communicate with another application layer, it forwards its data to the transport
There is an ambiguity occurs in the application layer. Every application cannot be placed inside the application layer except those who interact with the communication system. For example: text editor cannot be considered in application layer while web browser using HTTP protocol to interact with the network where HTTP protocol is an application layer

Following are the main protocols used in the application layer:

HTTP: HTTP stands for Hypertext transfer protocol. This protocol allows us to access the data over the world wide web. It transfers the data in the form of plain text, audio, video. It is known as a Hypertext transfer protocol as it has the efficiency to use in a hypertext environment where there are rapid jumps from one document to another.
SNMP: SNMP stands for Simple Network Management Protocol. It is a framework used for managing the devices on the internet by using the TCP/IP protocol suite.
SMTP: SMTP stands for Simple mail transfer protocol. The TCP/IP protocol that supports the e-mail is known as a Simple mail transfer protocol. This protocol is used to send the data to another e-mail
DNS: DNS stands for Domain Name System. An IP address is used to identify the connection of a host to the internet uniquely. But, people prefer to use the names instead of addresses. Therefore, the system that maps the name to the address is known as Domain Name

TELNET: It is an abbreviation for Terminal Network. It establishes the connection between the local computer and remote computer in such a way that the local terminal appears to be a terminal at the remote system.
FTP: FTP stands for File Transfer Protocol. FTP is a standard internet protocol used for transmitting the files from one computer to another computer.

IP Addressing or Network Addressing

Network Addressing is one of the major responsibilities of the network layer.
Network addresses are always logical, i.e., software-based
A host is also known as end system that has one link to the network. The boundary between the host and link is known as an interface. Therefore, the host can have only one
A router is different from the host in that it has two or more links that connect to it. When a router forwards the datagram, then it forwards the packet to one of the links. The boundary between the router and link is known as an interface, and the router can have multiple interfaces, one for each of its links. Each interface is capable of sending and receiving the IP packets, so IP requires each interface to have an address.
Each IP address is 32 bits long, and they are represented in the form of “dot-decimal notation” where each byte is written in the decimal form,and they are separated by the period. An IP address would look like 193.32.216.9 where 193 represents the decimal notation of first 8 bits of an address, 32 represents the decimal notation of second 8 bits of an address.

Classful Addressing

An IP address is 32-bit long. An IP address is divided into sub-classes:

Class A
Class B
Class C
Class D
Class E

An ip address is divided into two parts:

Network ID: It represents the number of
Host ID: It represents the number of

In the above diagram, we observe that each class has a specific range of IP addresses. The class of IP address is used to determine the number of bits used in a class and number of networks and hosts available in the class.

For example –

Class A

In Class A, an IP address is assigned to those networks that contain a large number of hosts.

The network ID is 8 bits
The host ID is 24 bits long.

In Class A, the first bit in higher order bits of the first octet is always set to 0 and the remaining 7 bits determine the network ID. The 24 bits determine the host ID in any network.

The total number of networks in Class A = 27 = 128 network address The total number of hosts in Class A = 224 – 2 = 16,777,214 host address

Subnetting

A subnet, or subnetwork, is a segmented piece of a larger network. More specifically, subnets are a logical partition of an IP network into multiple, smaller network segments. The Internet Protocol (IP) is the method for sending data from one computer to another over the internet. Each computer, or host, on the internet has at least one IP address as a unique identifier.

Organizations will use a subnet to subdivide large networks into smaller, more efficient subnetworks.

One goal of a subnet is to split a large network into a grouping of smaller, interconnected networks to help minimize traffic.

This way, traffic doesn’t have to flow through unnecessary routs, increasing network speeds

How subnets work

Each subnet allows its connected devices to communicate with each other, while routers are used to communicate between subnets.

The size of a subnet depends on the connectivity requirements and the network technology employed.

Network Address Translation – NAT

Network Address Translation (NAT) is a process in which one or more local IP address is translated into one or more Global IP address and vice versa in order to provide Internet access to the local hosts.

NAT generally operates on router or firewall. here are 3 types of NAT:

Static NAT – In this, a single private IP address is mapped with single Public IP address, i.e., a private IP address is translated to a public IP address. It is used in Web
DynamicNAT

In this type of NAT, multiple private IP address are mapped to a pool of public IP address. It is used when we know the number of fixed users wants to access the Internet at a given point of time.

Port Address Translation (PAT) – This is also known as NAT overload. In this, many local (private) IP addresses can be translated to single registered IP

Port numbers are used to distinguish the traffic i.e., which traffic belongs to which IP

This is most frequently used as it is cost effective as thousands of users can be connected to the Internet by using only one real global (public) IP

VLAN

VLAN, also known as virtual LAN, is a group of devices of one or more LANs regardless of physical location.

it allows devices to be grouped together even though they are not connected on the same fiber switch.
it often requires the network hardware/software to support VLAN functionality, for example,
VLAN switch is essential for setting up a VLAN
In VLAN, the configuration of the network can be done via software extensively. Basically, VLANs are used at layer 2 to break up broadcast domains.

VLAN and Subnet are both developed to deal with segmenting or partitioning a portion of the network. And
they share such similarities as restricting broadcast domains or ensuring security through isolation of different sub-networks.
However, there are obvious differences between them on operation, functionality and deeper

Proxy server and Web server

A proxy server is a dedicated computer or a software system running on a computer that acts as an intermediary between an endpoint device, such as a computer, and another server from which a user or client is requesting a
The proxy server may exist in the same machine as a firewall server or it may be on a separate server, which forwards requests through the
An advantage of a proxy server is that its cache can serve all
If one or more Internet sites are frequently requested, these are likely to be in the proxy’s cache, which will improve user response
A proxy can also log its interactions, which can be helpful for

How proxy servers work?

When a proxy server receives a request for an Internet resource (such as a Web page), it looks in its local cache of previously pages. If it finds the page, it returns it to the user without needing to forward the request to the Internet. If the page is not in the cache, the proxy server, acting as a client on behalf of the user, uses one of its own IP addresses to request the page from the server out on the Internet. When the page is returned, the proxy server relates it to the original request and forwards it on to the user.

Proxy servers are used for both legal and illegal purposes. In the enterprise, a proxy server is used to facilitate security, administrative control or caching services, among other purposes.

In a personal computing context, proxy servers are used to enable user privacy and anonymous surfing. Proxy servers can also be used for the opposite purpose: To monitor traffic and undermine user privacy.

To the user, the proxy server is invisible; all Internet requests and returned responses appear to be directly with the addressed Internet server. (The proxy is not actually invisible; its IP address has to be specified as a configuration option to the browser or other protocol program.)

Users can access web proxies online or configure web browsers to constantly use a proxy server. Browser settings include automatically detected and manual options for HTTP, SSL, FTP, and SOCKS proxies. Proxy servers may serve many users or just one per server. These options are called shared and dedicated proxies, respectively.

There are a number of reasons for proxies and thus a number of types of proxy servers, often in overlapping categories.

Forward and reverse proxy servers

Forward proxies send the requests of a client onward to a web server. Users access forward proxies by directly surfing to a web proxy address or by configuring their Internet settings. Forward proxies allow circumvention of firewalls and increase the privacy and security for a user but may sometimes be used to download illegal materials such as copyrighted materials

Reverse proxies transparently handle all requests for resources on destination servers without requiring any action on the part of the requester.

Reverse proxies are used:

To enable indirect access when a website disallows direct connections as a security
To allow for load balancing between
To stream internal content to Internet
To disable access to a site, for example when an ISP or government wishes to block a

Sites might be blocked for more or less legitimate reasons. Reverse proxies may be used to prevent access to immoral, illegal or copyrighted content.

Reverse proxies sometimes prevent access news sites where users could view leaked information.

They can also prevent users from accessing sites where they can disclose information about government or industry actions.

Other types of proxy servers

Transparent proxies are typically found near the exit of a corporate network.

These proxies centralize network traffic. On corporate networks, a proxy server is associated with — or is part of — a gateway server that separates the network from external networks (typically the Internet) and a firewall that protects the network from outside intrusion and allows data to be scanned for security purposes before delivery to a client on the network.

These proxies help with monitoring and administering network traffic as the computers in a corporate network are usually safe devices that do not need anonymity for typically mundane tasks.

Anonymous proxies hide the IP address of the client using them allow to access materials that are blocked by firewalls or to circumvent IP address bans.

DNS

When DNS was not into existence, one had to download a Host file containing host names and their corresponding IP address. But with increase in number of hosts of internet, the size of host file also increased. This resulted in increased traffic on downloading this file. To solve this problem the DNS system was introduced.

Domain Name System helps to resolve the host name to an address. It uses a hierarchical naming scheme and distributed database of IP addresses and associated names

Firewall

Firewall is a barrier between Local Area Network (LAN) and the Internet. It allows keeping private resources confidential and minimizes the security risks. It controls network traffic, in both directions.

The following diagram depicts a sample firewall between LAN and the internet. The connection between the two is the point of vulnerability. Both hardware and the software can be used at this point to filter network traffic

There are two types of Firewall system: One works by using filters at the network layer and the other works by using proxy servers at the user, application, or network layer.

Router

The router is a physical or virtual internetworking device that is designed to receive, analyze, and forward data packets between computer networks. A router examines a destination IP address of a given data packet, and it uses the headers and forwarding tables to decide the best way to transfer the packets. There are some popular companies that develop routers; such are Cisco, 3Com, HP, Juniper, D-Link, Nortel, etc. Some important points of routers are given below:

A router is used in LAN (Local Area Network) and WAN (Wide Area Network) environments. For example, it is used in offices for connectivity, and you can also establish the connection between distant networks such as from Bhopal to
It shares information with other routers in
It uses the routing protocol to transfer the data across a
Furthermore, it is more expensive than other networking devices like switches and

A router works on the third layer of the OSI model, and it is based on the IP address of a computer. It uses protocols such as ICMP to communicate between two or more networks. It is also known as an intelligent device as it can calculate the best route to pass the network packets from source to the destination automatically.

Mail Server and their respective configuration settings

Mail Server Settings & Mail Configuration

In order to fetch and send mails from the application, you need to configure the Mail Server Settings in the Admin module.

Incoming Mail Server Settings

It has the following fields –

Server Name/IP Address: Denotes the Incoming Mail Server from where the mails need to be
User Name & Password: Login credentials to the
Email Type: Indicates the type of email fetching (For example: IMAP or POP and so on)
Port: Port from where the mails need to be
Mail Loop & Mail Storming Prevention Settings: Suppress Auto Notification and prevent Email Storming from contacts by halting the mail looping and mail fetching into the application.Specify the number of mails and the time span after which the mail fetching and the looping should be

All fields are mandatory fields and cannot take null values. Click Save button after entering the above details. The configurations will be saved and SupportCenter Plus will try to establish connection with the mail server. Click Start Fetching button, to start the mail fetching.

Outgoing Mail Server Settings

It has the following fields –

Server Name/IP Address: Denotes the Outgoing Mail Server through which the mails are sent to the external
Alternate Server Name/IP Address: Backup server name which will take over the main server in case of server
Email Type: Indicates the type of email despatching (For example: SMTP or POP and so on).
Port: Port from where the mails need to be

If authentication is required for outgoing mails server, enable Required Authentication and enter the specific credentials.

Mail Configuration

The email address to which the service requests are sent and should be fetched by SupportCenter Plus application is configured under Mail Configuration. If you have enabled multi-tendency, the email address of the respective Business Units can be configured such that the mails are routed to the particular Business Unit.

Incoming Email IDs: The email address to which the service requests are
Sender Name: The name to appear in the mail beside sender’s mail ID, while sending mails from the
Reply-To Address: The email address to which the reply needs to be

Interconnecting Devices

Network Devices (Hub, Repeater, Bridge, Switch, Router, Gateways and Brouter)

Repeater – A repeater operates at the physical layer. Its job is to regenerate the signal over the same network before the signal becomes too weak or corrupted so as to extend the length to which the signal can be transmitted over the same network. An important point to be noted about repeaters is that

they do not amplify the signal. When the signal becomes weak, they copy the signal bit by bit and regenerate it at the original strength. It is a 2 port device.

Hub – A hub is basically a multiport repeater. A hub connects multiple wires coming from different branches, for example, the connector in star topology which connects different stations. Hubs cannot filter data, so data packets are sent to all connected devices. In other words, collision domain of all hosts connected through Hub remains one. Also, they do not have intelligence to find out best path for data packets which leads to inefficiencies and
Bridge – A bridge operates at data link layer. A bridge is a repeater, with add on the functionality of filtering content by reading the MAC addresses of source and destination. It is also used for interconnecting two LANs working on the same protocol. It has a single input and single output port,

Knowledge about various network related commands

Ping

Ping is used to testing a network host capacity to interact with another host.

Netstat

the netstat provides the statistics and information in the use of the current TCP-IP Connection network.

Ip Config

The command IP config will display basic details about the device’s IP address configuration.

Tracert

The tracert command is a Command Prompt command which is used to get network packet being sent and received and the number of hops required for that packet to reach to target. This command can also be referred to as a traceroute. It provides several details about the path that a packet takes from the source to the specified destination

Nslookup

The Nslookup which stands for name server lookup command is a network utility command used to obtain information about internet servers. It provides name server information for the DNS (Domain Name System) i