Tutorials :: The Linux Channel

Here is a code-walk of a git-hub source submitted by a viewer Sekhar Pariga, which is a Multi-client TCP Server with pthreads Mutex synchronized. Basically it is a Directory Listing Server, that serves ls, cd, pwd of directory functions to connecting TCP clients which are remotely (locally) executed by the server. Server is implemented using multi-thread pthread library, to serve multiple clients simultaneously. Server keeps the each accepted client session details in the queue data structure. Client session queue contains each clients socket-fd and present working directory as a queue node.

NIC Cards (Network Interface Cards) traditionally contain controller chip which takes care of the core aspects, such as packet reception, buffering (till they are read by OS device drivers), etc. But these days increasingly modern NIC cards can perform several CPU Network Offload functions such as packet/frame checksum, etc. Such hardware offload features of modern NIC cards is crucial to process packets and support packet data transfer rates of around 1Gbps, 10Gbps, even 40Gbps and so on. But beyond that such as 100Gbps and so on, at times even a high-end Xeon/ Intel/ AMD processors will struggle if need to support transfer rates of around 100Gbps or beyond (situations like Link Bonding). These are the situations we need what we call as Smart NIC Cards. A Smart NIC card implements most of the network traffic processing on the NIC itself that would necessarily be performed by the CPU (i.e Operating System) in the case of a traditional NIC card.

Here is a video series on TCP Link bonding (a.k.a Multihoming) and Multipath TCP (MPTCP). MPTCP is an ongoing effort of the Internet Engineering Task Force's (IETF) Multipath TCP working group, that aims at allowing a Transmission Control Protocol (TCP) connection to use multiple paths (via TCP sub-flows) to maximize throughput and increase redundancy.

Aqui está meu código de soquete UDP de amostra escrito em C. Ao contrário de outras versões, você costuma obter on-line, esta versão é voltada para desenvolvedores de software de rede e sistemas e como uma referência rápida até mesmo para programadores de software experientes. Neste exemplo / modelo, estou enviando bytes de dados binários brutos de teste do cliente de amostra UDP para o servidor de amostra UDP registrado. O código já possui documentação na forma de comentários (como você pode ver abaixo). Você pode baixar meu código-fonte abaixo e você pode usá-lo diretamente em seus projetos ou você pode usar o mesmo para fins de aprendizagem para entender sobre a programação de soquete de espaço do usuário via protocolo de camada de transporte UDP IPv4.

Here is my sample UDP socket code written in C. Unlike other versions you get commonly on-line this version is focused towards systems and network software developers and as a quick reference even for experienced software programmers. In this example/template, I am sending test raw binary data bytes from UDP sample client to registered UDP sample server. The code has documentation already in the form of comments (as you can see below). You can download my source below and you can use it directly in your projects or you can use the same for learning purposes to understand about user-space socket programming via IPv4 UDP transport layer protocol.

Here is my sample Kernel Module to drop packets (i.e sk_buff instance) captured via netfilter hooks. When you want to drop packets in your custom netfilter hooks make sure you never do a manual kfree_skb(skb) API call. Since it is anyway performed once the flow of the code moves out of your kernel module netfilter hook. All you need to do is to return NF_DROP to drop gracefully the desired packet. Here is my detailed video and a sample Linux Kernel module.

Linux Networking Stack Receive Flow Steering (RFS) aim is to increase data-cache hitrate by steering kernel processing of packets to the CPU where the application thread consuming the packet is running. RFS relies on the same RPS mechanisms to enqueue packets onto the backlog of another CPU and to wake up that CPU.

There can be many ways one can architect VPN Networks. The end objective is to tunnel private IP (typically LAN subnets) within public IP Networks (such as Internet). You can establish such a tunnel in various creative ways, such as Transport Mode, Tunnel Mode, IP-in-IP tunneling, etc. Also you can choose any transport layer protocol of your choice such as send VPN traffic via TCP, or via UDP and so on.