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Linux Network Management

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Linux Network Management

  1. 1. © 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Linux Network Management
  2. 2. 2© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. What to Expect? W's of Networking Introduction to Sockets Addressing at the Layers Programming the Sockets Client-Server Concepts
  3. 3. 3© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. W's of Networking Communication is the Key User Space & User Space Signals, IPC, Shared Address Space Kernel Space & User Space System Calls, Signals Kernel Space & Kernel Space Kernel Communication & Synchronization Mechanisms Hardware Space & Kernel Space Interrupts, Device Access Mechanisms What's common in all of these? All within the same system Networking extends a hand outside the system
  4. 4. 4© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Network Stack & Sockets Physical Data Link Network Transport Session Presentation Application Stream Socket Interface Datagram Socket Interface Raw Socket Interface IP Application Program 7 Layers TCP UDP Interface Layer (Ethernet, SLIP, loopback, etc) Media
  5. 5. 5© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. System I Inter System Communication User Space ...Process Process Socket Interface Kernel Space Hardware Space System II User Space ...Process Process Socket Interface Kernel Space Hardware Space Network Link D
  6. 6. 6© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Examples Network Daemons (Servers) with default socket numbers ftpd (Port 21) sshd (Port 22) telnetd (Port 23) smtp (Port 25) httpd (Port 80) Network Applications (Clients) ftp ssh telnet Mail Clients (pine, mutt, ...) Web Browsers (firefox, ...)
  7. 7. 7© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. System Dependence Wire Transmission – Bit-wise MSB first System Data – Word-wise Which end first? Depends on the Processor Two prevalent Endians Little Endian (x86 systems, PPC, ...) Big Endian (Sun systems, PPC, ...)
  8. 8. 8© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Little Endian 00101000 01111100 00101110 00101010 Data MS Byte LS Byte Memory A A+1 A+2 A+3 00101010 00101110 01111100 00101000
  9. 9. 9© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Big Endian 00101000 01111100 00101110 00101010 00101010 00101110 01111100 00101000 Memory Data MS Byte LS Byte A A+1 A+2 A+3
  10. 10. 10© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Trivial functions uint16_t htons(uint16_t host_short); uint16_t ntohs(uint16_t network_short); uint32_t htonl(uint32_t host_long); uint32_t ntohl(uint32_t network_long); Header: <arpa/inet.h>
  11. 11. 11© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Addressing at Layers Physical Data Link Network Transport Session Presentation Application IP TCP UDP Application Program Physical Networks Physical Address (MAC Address) IP Address Port Address (Socket Address) User-specific
  12. 12. 12© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Socket Address Basic Structure (16 bytes) struct sockaddr { sa_family_t sa_family; // Protocol Family char sa_data[14]; // Protocol Address } typedef unsigned short sa_family_t;
  13. 13. 13© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Socket Address ... With Internet Address struct sockaddr_in { sa_family_t sin_family; // Protocol Family in_port_t sin_port; // Port Number / Socket Address struct in_addr sin_addr; // IP Protocol Address unsigned char sin_zero[8]; // Pad to sizeof(struct sockaddr) } typedef uint16_t in_port_t; struct in_addr { in_addr_t s_addr; } typedef uint32_t in_addr_t;
  14. 14. 14© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Socket Programming Usage Socket Creation: socket() Attaching with an address: bind() Preparing for accepting connections: listen() Waiting for & Accepting connections: accept() Setting up the connection: connect() Sending data: send(), sendto(), sendmsg() Receiving data: recv(), recvfrom(), recvmsg() Cleaning up: close() Example Pairs Connection-oriented (TCP based): sock_server.c, sock_client.c Connection-less (UDP based): sock_dgram_*.c
  15. 15. 15© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Creating a socket fd = socket(family, type, protocol); Family AF_UNIX / AF_LOCAL, AF_INET, AF_INET6, ... Type SOCK_STREAM, SOCK_DGRAM, SOCK_RAW, ... Can be or'ed with SOCK_NONBLOCK, SOCK_CLOEXEC Protocol Typically one per family. So, pass zero Returns file descriptor of the new socket on success -1 on error (and sets errno)
  16. 16. 16© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Attaching an address Done by a server status = bind(fd, addresssp, addrlen); fd: File descriptor returned by socket() addressp: Pointer to address structure addrlen: Size of address structure Returns 0 on success -1 on error (and sets errno)
  17. 17. 17© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Preparing for connections Done by a server for transport connections status = listen(fd, qlen); fd: File descriptor returned by socket() qlen Length of the pending connection queue Returns 0 on success -1 on error (and sets errno)
  18. 18. 18© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Accepting new connections Done by a server for connection based sockets newfd = accept(fd, addresssp, addrlen); fd: File descriptor returned by socket() addressp (Could be NULL) Pointer to structure of address of the connected peer addrlen: Value-result address structure size Blocking call (by default), waiting for new connections Returns File descriptor of the new accepted socket connection -1 on error (and sets errno)
  19. 19. 19© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Connecting to server Done by a client for connection based sockets status = connect(fd, addresssp, addrlen); fd File descriptor returned by socket() to be connected addressp Pointer to structure of address to connect to addrlen: Size of address structure Returns 0 on success -1 on error (and sets errno)
  20. 20. 20© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Connection Establishment Server Application socket() bind() listen() accept() Physical Layer Transport / Network Layer Client Application socket() connect() Transport / Network Layer
  21. 21. 21© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Sending Data Could be done by both server and client sent = send(fd, buf, len, flags); fd: File descriptor of the connected socket buf: Buffer of Data to be sent len: Length of the data to be sent flags: MSG_DONTWAIT, MSG_NOSIGNAL, ... Returns Bytes of data sent on success -1 on error (and sets errno) Other APIs: write(), sendto(), sendmsg()
  22. 22. 22© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Receiving Data Could be done by both server and client received = recv(fd, buf, len, flags); fd: File descriptor of the connected socket buf: Buffer to receive Data into len: Length of the Buffer flags: MSG_DONTWAIT, MSG_PEEK, MSG_WAITALL, ... Returns Bytes of data received on success -1 on error (and sets errno) Other APIs: read(), recvfrom(), recvmsg()
  23. 23. 23© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Closing sockets To be done by both server and client On all the not-needed socket file descriptors Unless they were opened with SOCK_CLOEXEC Terminates both directions of data transfer Reading and Writing Cleans up all the socket related resources shutdown(fd, how); fd: File descriptor of the socket to be closed how: SHUT_RD, SHUT_WR, SHUT_RDWR Returns 0 on success -1 on error (and sets errno) Other API: close()
  24. 24. 24© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Non-blocking Options Typical blocking system calls accept() send*(), write() recv*(), read() Achieving non-blocking behaviour Non-blocking: Socket opened with SOCK_NONBLOCK Multiplexing: Use select() or poll() or epoll() on socket fd Signal driven: Set socket to deliver SIGIO on activity Using FIOSETOWN cmd of fcntl, Or Using SIOCSPGRP cmd of ioctl
  25. 25. 25© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. System Call 'select' Header File: <sys/select.h> int select( int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout ); File Descriptor Set APIs void FD_ZERO(fd_set *set); void FD_SET(int fd, fd_set *set); void FD_CLR(int fd, fd_set *set); int FD_ISSET(int fd, fd_set *set); Select Usage Example: pipe_window.c → pipe_window0, pipe_window1 Server-Client Pair: sock_server_select.c, sock_client.c
  26. 26. 26© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. System Call 'poll' Header File: <poll.h> int poll( struct pollfd *array_fds, nfds_t nfds, struct timespec *timeout ); struct pollfd int fd; short events /* requested events */ short revents /* returned events */ Events: POLLIN, POLLOUT, POLLPRI Additional returned Events: POLLERR, POLLHUP, POLLNVAL
  27. 27. 27© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Socket related Information cat /proc/sys/net/core/ rmem_default: Default receive buffer size rmem_max: Maximum receive buffer size wmem_default: Default send buffer size wmem_max: Maximum send buffer size … man 7 socket
  28. 28. 28© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Client-Server Concepts Types of Connections Control connections Data connections Types of Servers Iterative servers (Single Process) Concurrent servers (Multi-Process)
  29. 29. 29© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Iterative Servers Client Server Client Ephemeral Port Well-known Port Example: sock_server_select.c(, sock_client.c)
  30. 30. 30© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Concurrent Servers Client Server Client Child Server Ephemeral Port Well-known Port Example: sock_server_concurrent.c(, sock_client.c) Child Server
  31. 31. 31© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Miscellaneous Examples Named (AF_UNIX / AF_LOCAL) Sockets named_socket_server.c named_socket_client.c Multicast Operations mcast_recv.c mcast_send.c
  32. 32. 32© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. What all have we learnt? W's of Networking Introduction to Sockets Networking with 'Endian' Addressing at the Layers Programming the Sockets Client-Server Concepts
  33. 33. 33© 2010-17 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Any Queries?

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