UDP sockets This article describes how to write a simple echo server and client using udp sockets in C on Linux/Unix platform. UDP sockets or Datagram sockets are different from the TCP sockets in a number of ways. The most important difference is that UDP sockets are not connection oriented. More technically speaking, a UDP… Read More »
Socket function – recv() If you are writing a socket program in python that communicates with some remote machine or server to receive data, then you shall be using the recv() function to receive data on a socket. The recv() can receive only a specified number of bytes into a string buffer. If the incoming… Read More »
In a previous example we learnt about the . In this example we shall build a basic ECHO client and server. The server/client shown here use TCP sockets or SOCK_STREAM. Tcp sockets are connection oriented, means that they have a concept of independent connection on a certain port which one application can use at a… Read More »
Socket programming in Java This is a quick guide/tutorial to learning socket programming in Java. The Socket class is documented at http://docs.oracle.com/javase/1.4.2/docs/api/java/net/Socket.html To summarise the basics, sockets are the fundamental “things” behind any kind of network communications done by your computer. For example when you type www.google.com in your web browser, it opens a socket… Read More »
Tutorial on how to code simple network servers and clients using low level Socket api in python.
Php and tcp/ip sockets This is a quick guide to learning socket programming in php. Socket programming php is very similar to C. Most functions are similar in names, parameters and output. However unlike C, socket programs written in php would run the same way on any os that has php installed. So the code… Read More »
This is a small script written in php that can fetch the whois information of an ip address from regional internet registries (RIR). Useful in finding information about ip address.
MAC Address The mac address (media access control address) or the hardware address or the ethernet address of an interface is a 48 bit number that looks like this : 00:1c:c0:f8:79:ee. Every machine connected to a network has a unique mac address that is used to deliver network packets to the correct machine. The mac… Read More »
On a Linux system, all network interfaces have a unique name that is shows up when you run the ifconfig command for example. The main network adapter often has the name eth0 or enp1s0 on linux systems. The ip address is configured using desktop gui tools, or through commands like ifconfig. If you are writing… Read More »
Theory The whois information of an ip address provides various details like its network, range, isp etc. This information is maintained by various regional registry servers. Read the wikipedia article on regional internet registries for more information. There are a total of 5 regional registries spanning various geographical regions of the world. For example if… Read More »
Socket programming with winsock This is a quick guide/tutorial to learning socket programming in C language on Windows. “Windows” because the code snippets shown over here will work only on Windows. The windows api to socket programming is called winsock. Sockets are the fundamental “things” behind any kind of network communications done by your computer…. Read More »
Handle multiple socket connections When writing server programs using sockets , it becomes necessary to handle multiple connections at a time , since a server needs to serve multiple clients. There are many ways to do so. On linux this can be done in various ways like forking , threading , select method etc. In… Read More »
Learn socket programming in C on the linux platform. Write socket servers and client programs in C.
Wxpython is the python port of wxwidgets gui library. On ubuntu wxpython can be installed from synaptic. On windows it can be downloaded from the website wxpython.org And here is a small program that pops up a simple window , to take a domain name and perform a whois for that domain. #!/usr/bin/python ''' GUI… Read More »
Whois A whois client is a program that will simply fetch the whois information for a domain/ip address from the whois servers. The code over here works according to the algorithm discussed here. A whois server runs a whois service on port 43 (whois port). We need to connect to this port with sockets and… Read More »
Local Ip address The local ip is the source ip in IP packets send out from a system. When the system is a part of a local area network then the local ip in most cases is something like 192.168.*.* . The network interface (eth0) is assigned an ip address of that range. However when… Read More »
Winpcap Winpcap is a packet capture library for Windows used for packet sniffing and sending raw packets. Wireshark is a popular sniffer tool that uses winpcap to sniff packets. Here is a sample code which shows how winpcap can be used to sniff incoming packets on a particular interface. Code /* Simple Sniffer with winpcap… Read More »
MAC Address Mac address (Media Access Control Address) or hardware address is a 48 bit (6 character) wide address assigned to a network interface. It is important for the packet delivery between 2 devices like your computer and the router. Ethernet protocol uses the mac address to deliver it to the right network node. It… Read More »
Socket applications often need to convert hostnames like google.com to their corresponding ip address. This is done through dns requests. The socket api in linux provides functions like gethostbyname and getaddrinfo that can be used to perform the dns requests and get the ip address. 1. gethostbyname The first method uses the traditional gethostbyname function… Read More »
In the previous part we made a simple sniffer which created a raw socket and started receiving on it. But it had few drawbacks : 1. Could sniff only incoming data. 2. Could sniff only TCP or UDP or ICMP or any one protocol packets at a time. 3. Ethernet headers were not available. In… Read More »