Currently viewing the category: "Linux Network Programming"

TCP TIME_WAIT State and Address Already in Use Error

By On January 25, 2012 · Leave a Comment

0. The Problem
Recently I am working on a project consists of TCP socket programming on Linux. I encountered errno 98 (address already in use) and 99 (cannot assign requested address) frequently. I wrote a small test program to reproduce the issue. The test code is as below,

#include <stdio.h>

#include <stdlib.h>

[...]

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Simple TCP Socket Client and Server Communication in C Under Linux

By On December 2, 2011 · 3 Comments

This post doesn’t provide details about how Linux socket works, its design etc. It mainly for providing source code of simple TCP socket client and server in C. I’m writing this because I found myself need simple TCP client and server for testing from time to time.
1. The TCP Server Code

You can [...]

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How to Calculate IP/TCP/UDP Checksum–Part 3 Usage Example and Validation

By On November 27, 2011 · 2 Comments

This is a follow up of the previous post IP/TCP/UDP Checksum Calculation part 1 theory, and part 2 implementation.

This post gives an example using libnetfiler_queue library and the checksum code we implemented in part 2 to illustrate how to use the checksum code and verify that our code [...]

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How to Calculate IP/TCP/UDP Checksum–Part 2 Implementation

By On November 27, 2011 · Leave a Comment

This is a follow up of the previous post, how to calculate IP/TCP/UDP checksum part 1 — theory.

IP Header Checksum Calculation Implementation
To calculate the IP checksum, one can use the code below,

/* set ip checksum of a given ip header*/

void compute_ip_checksum(struct iphdr* iphdrp){

iphdrp->check = 0; [...]

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How to Calculate IP/TCP/UDP Checksum–Part 1 Theory

By On November 27, 2011 · Leave a Comment

This is the first part of How to Calculate IP/TCP/UDP Checksum. The 2 parts followed are Part 2 Implementation and Part 3 Usage Example and Validation.

This part focuses on the algorithms. We’ll go through IP/TCP/UDP one by one.

IP Header Checksum Calculation

IP checksum is a 16-bit field in IP [...]

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