Basics of IP, ICMP

IP Internet Protocol 

IP is the internet layer. It uses each packet’s Address. It uses routing Table by which it decides where a packet is to be sent choosing its best path

An IP Header feature are as below;

• Version : it describes IP version no.
• Header length: HLEN in 32 bit
• Priority & Type of Service: It describes how the datagram should be handled.
• Total Length: Length of the packet including header & data.
• Identification: Unique IP Packet value used to differentiate fragmented packets from diff data grams.
• Flags : Specifies whether fragmentation should occur.
• Fragment offset: provides fragmentation & allows different maximum transmission unit MTUS on the internet.
• TTL : Time to Leave: TTL is set in to the packet when generated for reaching at destination within time limit. Otherwise it get Lost.
• Protocol : Port of upper layer protocol. (tcp-6 & udp-17)
• Header Check sum: CRC (Cyclic Redundancy Check Only) on header.
• Source IP Address: 32-bit IP address of Sender.
• Destination IP address: 32-bit IP address of Receiver/ Destination .
• Options: It is Used for testing [ network, debug, security].
• Data: After the IP option field is the upper layer data.

   ICMP : Internet Control Message Protocol parameters

I

Basics of Telnet and other protocols

Some useful networking protocols in brief

Telnet (Terminal Emulation):

It Allows Users from remote client system to connect or access other client system or resources, Servers. By using telnet client software one can access/log in to  the server.

SMTP (Simple Mail Transfer Protocol):

Doing the process for email delivery, message queuing , checking the message, spooling the message.

TFTP (Trivial File Transfer Protocol):

It is being used only for sending and receiving files of very small amount mean small data. It does not have directory browsing facility and it is not secure method .

FTP (FILE TRANSFER PROTOCOL):

It is the real protocol used for transfer for files. it is not just a protocol but also a programme. Most of FTP client and server software are now available to the market. It have authentication of users , allows to access the directories of files, browsing of directory, copy paste options.

It is faster than email while sending or receiving Large Files while we know some email services provide max 25 MB of data to be attached.

IMAP(Internet Message Access Protocol):

Used for making control over mails, downloading mails, Gives option for search mail with commands based on message subject, header, to mail etc. You  can store mails on mail Server. Now its being used as Version 4 and so far called IMAP4. Before IMAP there was POP ( Post Office protocol ) which was earlier used to store incoming mail but it does not allow to download mails selectively. 

SNMP(Simple Network Management protocol):

This protocol Collects & Pulls valuable network information, gathers the data of the devices connected in a network with some time intervals. This protocol also notices and alerts any events happening in a network.

version 1, 2, 3 available. v3 have more security, encryption and authenticity option.

SSH ( Secure Shell ):

It conducts a secure telnet session over a standard tcp/ip connection. And is assigned for logging in to systems, running programs on remote system, moving files from one system to another, remote command execution. Client software available freely like putty, open ssh. 

SSH CONNECTION

HTTP ( HYPERTEXT TRANSFER PROTOCOL ):

It is used to manage communications between web browser and web servers when we click on a link for any resource. It retrieves the data as per its name from different location around the world.

HTTPS ( Secure ):

 Its a Secure Protocol for HTTP and it uses secure socket layer.It enables you to do transactions online secure, whether in any log in process or for eCommerce use.

DNS:

Domain Name Service ( System ) 

It resolves Host name. DNS allows to use the domain name HOSTs to specify IP Address. It is being easy to remember than the IP Address, so it uses Alphabetic characters. Similarly the domain name converts it in to respective IP Addresses.

 After that a DNS is used to resolve a FQDN ( Fully Qualified Domain Name ).It specifies the exact location of the Domain name i.e. Host name + Domain Name. The DNS Server solves it by using the looking of DNS Table.

DHCP:

Dynamic Host Configuration Protocol

It Assigns IP Address to Hosts/clients . It allows Administration and control over a network of small or Large.

A DHCP Server provides the information as : 

•  IP Address
•  Subnet Mask
•  Domain Name
•  Default Gateway { IP Address of Router }
•  DNS Server address
•  WINS Server Address

Hence the DHCP conflict occurs in a network when there are Two same IP Address is given to two Hosts.

While assigning IP Address, It checks the availability of IP address by pinging request then resumes in the network.

Post Office Protocol (POP):

The POP protocol uses basically in email messaging. It provides the storage facility for all incoming mail. The used POP is called POP3.

Transport Layer Security (TLS):

The TLS protocol is one of the encryption protocol same as SSL (Secure Socket Layer) protocol. It enables secure online data transfer during browsing,  messaging, etc.

ARP

An Address Resolution Protocol (ARP) finds the hardware address of host from a known IP address. When IP has a datagram to send, it must inform a Network Access protocol, such as Ethernet or Token Ring, of the destination’s hardware address on the local network. ARP resolves IP addresses to Ethernet addresses.

-DR

Basics of TCP, UDP & Common used Ports

TCP

Transmission Control Protocol

It is the Transmission Layer Protocol  and was created to maintain communication.

TCP takes large  block of information from an application and breaks them in to different segments. It is a Connection Oriented Protocol means stable in connection with applications.

A connection oriented protocol is used in TCP have the establishment sequence in three-way handshake type. It allows the system to exchange information such as initial sequence number, windows size and other TCP parameters between client and web server. It happens prior to data transmission.

The TCP Segment works for Internet Layer, sending of packet from one source to destination. A TCP Header is 20 bytes long or up to 24 bytes with options.

There are some other protocols used for applications which are as:

Telnet, SMTP, HTTP, FTP, DNS, HTTPS, SSH, POP3, NTP, IMAP4

A Typical Segment or TCP Frame is as :-

Size of the frame:-

1. Source Port : 16 bit

2. Destination Port : 16 bit

3. Sequence Number : 32 bit

4. Acknowledgement No : 32 bit

5. Header : 4 bit

6. Windows Size : 16 bit

7. Checksum : 16 bit

8. Urgent pointer : 16 bit

9. Options : multiple of 32 bits

On the other  features are as : - 

• It  is Sequenced
• Reliable 
• Acknowledgement 
• Connection-oriented 
• Window  Flow Control
• Error Free Data Transfer
• Congestion Control
• Re transmission of  Lost packets.
• It Uses Virtual Circuit for establishing a connection.

The SYN and ACK flags are very important for the connection-oriented session establishment. When SYN bit is set, it means synchronize the sequence numbers (during connection setup), while ACK bit is used to indicate that the value in the acknowledgment field is valid. And then the ACK replied by the web server acknowledges the receipt of the web browser’s SYN message.

Configuring IP Address for IPv4 system. Just a basic knowledge. 

An IP address or Internet Protocol Address is a numerical level assigned to each device.

UDP: User Datagram Protocol

UDP is a connectionless and unreliable data delivery service with 32 bit structure. It have no error recovery, no sequencing, no recording, no acknowledgement, no congestion control.

Applications use UDP are tolerant to data lost during video streaming kind of transmission and handles their own reliability.

One advantage in UDP that it supports Multiplexing. 

Different types of Ports

A port is a communication point or one endpoint. The port number is a 16-bit unspecified integer, ranging from 0 to 65535. 

In networking some common port numbers used such as;

• Port no 20 & 21: Used for FTP (File Transfer Protocol)
• Port no 22: Used for SSH
• Port no 23: Used for Telnet
• Port no 67/68: Used for DHCP
• Port no 80: Used for HTTP
• Port no 443: Used for HTTPS
• Port no139 and 445: Used for SMB
• Port no 53: Used for DNS
• Port no 110: Used for POP3
• Port no 25: Used for SMTP
• Port no 8080: Used for Internet
• Port no 123: Used for NTP server
• Port no 161: Used for SNMP

There is always a common delusion that an open port is dangerous. This is largely due to lack of understanding into the use of open ports. Open ports are important to communicate transversely in the Internet. However, an open port can be dangerous when the service listening to the port is not patched, is exploitable, misconfigured or has poor network security policies.

-DR