Tag: #networking

Redis Sentinel provides high availability for Redis. We start a Redis master, then three Redis Sentinel instances. They discover each other, then we trigger a failover. 2019-01-08

Use nc (netcat) to create a web server that returns custom HTTP responses. 2018-12-31

HTTP keep-alive allows reusing the same TCP connection for multiple requests, avoiding the overhead of opening a new connection. HTTP request pipelining sends multiple requests without waiting for their responses. 2018-03-27

nc can create UDP connections. UDP connections are established when the first data packet is sent, and terminated when the server becomes unreachable. ICMP messages notify the client of an unreachable server. 2018-03-04

NAT allows multiple devices in a local network to share a single public IP address. Routers modify IP and port information in network packets, and manage a translation table. 2018-03-02

Linux uses exponential backoff to retry dropped TCP connections, with a configurable retry limit. 2018-02-27

TCP uses sequence numbers to map unordered IP packets to an ordered byte stream. The sequence number field is 32 bits, but wraps around to 0 after reaching the max value. The sender chooses a random “initial sequence number” during the connection handshake. 2018-02-24

tcpdump captures network traffic. Capture and analysis of a TCP connection, including the 3-way handshake and message exchange. 2018-02-23

IP addresses are mapped to MAC addresses using the Address Resolution Protocol (ARP). The OS maintains an ARP cache to store these mappings. 2018-02-11

Subnets divide the IP address space hierarchically using bitstring prefixes. We check if an IP address is in a subnet using C. 2018-02-10

Reverse DNS lookup maps an IP address to a domain name by querying PTR records. The mapping is not always consistent with the forward DNS lookup. 2018-02-09

ping uses ICMP, or “Internet Control Message Protocol”, to send “echo request” packets and receive “echo reply” packets. 2018-02-07

DHCP dynamically assigns IP addresses to hosts, using a client-server protocol over UDP. It involves a sequence of DORA (Discover, Offer, Request, Acknowledge) messages to obtain and configure a network lease. 2018-02-06

DNS resolution is a recursive procedure involving different record types like A, CNAME, and NS. Resolving a domain name can require multiple DNS queries to different nameservers. 2017-11-25

Authoritative DNS servers provide definitive responses for their domains, while recursive DNS servers consult other servers to serve responses, caching results to reduce load on authorities. 2017-08-20

Using the Go "net" package to look up IP addresses for a given domain name, using either the C stdlib or a pure Go DNS resolver. 2017-08-03

Examines Redis’s source code to understand how it tracks subscriptions, handles disconnections, and implements pattern subscriptions, highlighting potential pitfalls and attack vectors. 2017-03-01

Focused on learning C, UNIX, and networking fundamentals. To avoid becoming a neckbeard, I’ll keep my projects grounded in real-world applications. March will be dedicated to Vidrio. 2017-03-01

A TCP server that uses pthread to serve multiple clients concurrently, with an “echo” server for each connection. 2017-02-28

The domain and type arguments to socket() describe the protocol family and socket type, respectively. The protocol argument specifies the actual protocol to use, which may be inferred from the domain and type. 2017-02-27

A TCP server that uses the fork system call to create a new child process for each accepted connection, allowing it to handle multiple clients concurrently. 2017-02-25

lsof lists open system resources, including pipes, sockets, and yes, files. It shows their type, owner, and location. 2017-02-20

GeoDNS uses geo-IP to locate clients and connect them to the nearest server, reducing latency. 2017-02-08

Realtime apps use protocols like HTTP streaming, long polling, WebSocket to enable live updates. Scaling pub/sub requires distributed servers and routing clients to the closest server. 2017-02-04

The RTCDataChannel API lets us configure the delivery guarantees, including the ordered, maxPacketLifeTime, and maxRetransmits properties. 2017-01-17

Including setting up the RTCPeerConnection, creating a data channel, handling ICE candidates, and generating an offer to be shared with the remote peer. The signaling channel is copy-paste! 2017-01-16

STUN is a protocol that allows clients to discover their public IP address and port, enabling peer-to-peer connections in WebRTC. 2017-01-15

IP packets travel at ~20% the speed of light, with most time spent in routers rather than on the wire. 2017-01-01

The structure and contents of a DNS request datagram, including the header, question section, and how to represent it in C. 2016-12-31

An IP packet contains a ‘protocol number’ that identifies the protocol (e.g. TCP, UDP) running over IP. The kernel uses this to determine how to handle the packet. 2016-12-23

htons and htonl convert values between host and network byte order, where network order is big-endian. ntohl and ntohs are the inverse functions. 2016-12-21

The syscalls needed for a simple UDP echo server are socket, bind, recvfrom, sendto, and close. 2016-12-19

Kqueue is a more efficient alternative to select for managing multiple TCP connections, providing a publish-subscribe model for tracking events in the kernel. 2016-12-18

A minimal TCP server in C uses the socket, bind, listen, accept, recv, send, and close syscalls to manage connections. 2016-12-14

A UDP server that listens for packets and prints the received messages. A UDP client that sends “hello” to the server. 2016-11-17