FTP & TFTP

FTP (File Transfer Protocol)FTP is a network protocol used to transfer files from one computer to another over a TCP network. Like Telnet, it uses a client-network arhitecture, which means that a user has to have an FTP client installed to access the FTP server running on a remote machine. After establishing the FTP connection, the user can download or upload files to and from the FTP server.Consider the following example:A user wants to transfer files from Host A to the FTP server. The user will Read more [...]

Telnet & SSH

TelnetTelnet is a network protocol that allows a user to communicate with a remote device. It is a virtual terminal protocol used mostly by network administrators to remotely access and manage devices. Administrator can access the device by telnetting to the IP address or hostname of a remote device.To use telnet, you must have a software (Telnet client) installed. On a remote device, a Telnet server must be installed and running. Telnet uses the TCP port 23 by default.One of the greatest disadvantages Read more [...]

DHCP & DNS

DHCP (Dynamic Host Configuration Protocol)DHCP is a network protocol that is used to assign various network parameters to a device. This greatly simplifies administration of a network, since there is no need to assign static network parameters for each device.DHCP is a client-server protocol. A client is a device that is configured to use DHCP to request network parameters from a DHCP server. DHCP server maintains a pool of available IP addresses and assignes one of them to the host. A DHCP server Read more [...]

ARP (Address Resolution Protocol) explained

ARP (Address Resolution Protocol) is a network protocol used to find out the hardware (MAC) address of a device from an IP address. It is used when a device wants to communicate with some other device on a local network (for example on an Ethernet network that requires physical addresses to be known before sending packets). The sending device uses ARP to translate IP addresses to MAC addresses. The device sends an ARP request message containing the IP address of the receiving device. All devices Read more [...]

Ports explained

A port is a 16-bit number used to identify specific applications and services. TCP and UDP specify the source and destination port numbers in their packet headers and that information, along with the source and destination IP addresses and the transport protocol (TCP or UDP), enables applications running on hosts on a TCP/IP network to communicate.Applications that provide a service (such as FTP and HTTP servers) open a port on the local computer and listen for connection requests. A client can request Read more [...]

Internet Control Message Protocol (ICMP)

ICMP (Internet Control Message Protocol) is a network layer protocol that reports errors and provides information related to IP packet processing. ICMP is used by network devices to send error messages indicating, for example, that a requested service is not available or that a host isn’t reachable.ICMP is commonly used by network tools such as ping or traceroute. Consider the following example that illustrates how ping can be used to test the reachability of a host:Host A wants to test whether Read more [...]

UDP explained

One other important protocol in the TCP/IP site is User Datagram Protocol (UDP). This protocol is basically a scaled-down version of TCP. Just like TCP, this protocol provides delivery of data between applications running on hosts on a TCP/IP network, but, unlike TCP, it does not sequence the data and does not care about the order in which the segments arrive at the destination. Because of this it is considered to be an unreliable protocol. UDP is also considered to be a connectionless protocol, Read more [...]

IP header

An IP header is a prefix to an IP packet that contains information about the IP version, length of the packet, source and destination IP addresses, etc. It consists of the following fields:Here is a description of each field:Version – the version of the IP protocol. For IPv4, this field has a value of 4.Header length – the length of the header in 32-bit words. The minumum value is 20 bytes, and the maximum value is 60 bytes.Priority and Type of Service – specifies how the datagram should be Read more [...]

TCP/IP suite of protocols

The TCP/IP suite is a set of protocols used on computer networks today (most notably on the Internet). It provides an end-to-end connectivity by specifying how data should be packetized, addressed, transmitted, routed and received on a TCP/IP network. This functionality is organized into four abstraction layers and each protocol in the suite resides in a particular layer.The TCP/IP suite is named after its most important protocols, the Transmission Control Protocol (TCP) and the Internet Protocol Read more [...]

APIPA (Automatic Private IP Addressing)

Automatic Private IP Addressing (APIPA) is a feature in operating systems (such as Windows) that enables computers to automatically self-configure an IP address and subnet mask when their DHCP server isn’t reachable. The IP address range for APIPA is 169.254.0.1-169.254.255.254, with the subnet mask of 255.255.0.0.When a DHCP client boots up, it looks for a DHCP server in order to obtain network parameters. If the client can’t communicate with the DHCP server, it uses APIPA to configure itself Read more [...]

TCP explained

One of the main protocols in the TCP/IP suite is Transmission Control Protocol (TCP). TCP provides reliable and ordered delivery of data between applications running on hosts on a TCP/IP network. Because of its reliable nature, TCP is used by applications that require high reliability, such as FTP, SSH, SMTP, HTTP, etc.TCP is connection-oriented, which means that, before data is sent, a connection between two hosts must be established. The process used to establish a TCP connection is known as Read more [...]

Traceroute explained

Traceroute is a command-line interface based tool used to identify the path used by a packet to reach its target. This tool also uses ICMP messages, but unlike ping, it identifies every router in a path taken by the packets. Traceroute is useful when troubleshooting network problems because it can help identify where exactly the problem is. You can figure out which router in the path to an unreachable target should be examined more closely as the probable cause of the network’s failure.Traceroute Read more [...]

NTP (Network Time Protocol)

Network Time Protocol (NTP) is an application layer protocol used for clock synchronization between hosts on a TCP/IP network. The goal of NTP is to ensure that all computers on a network agree on the time, since even a small difference can create problems. For example, if there is more than 5 minutes difference on your host and the Active Directory domain controller, you will not be able to login into your AD domain.NTP uses a hierarchical system of time sources. At the top of the structure are Read more [...]

HTTP and HTTPS explained

HTTP (Hypertext Transfer Protocol)HTTP is an client-server protocol that allows clients to request web pages from web servers. It is an application level protocol widely used on the Internet. Clients are usually web browsers. When a user wants to access a web page, a browser sends an HTTP Request message to the web server. The server responds with the requested web page. By default, web servers use the TCP port 80.Clients and web servers use request-response method to communicate with each other, Read more [...]
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