Socket options: a summary

1

• Socket options a summary
• Tcp options, ip options and general socket
  options can be examined and sometimes modified.
• getsockopt, setsockopt
• fcntl
• Ioctl
• include ltsys/socket.hgt
• int getsockopt (int sockfd, int level, int
  optname, void optval, socklen_t optlen)
• Int setsockopt(int sockfd, int level, int
  optname, const void optval, socklen_t optlen)

2

• include ltsys/socket.hgt
• int getsockopt (int sockfd, int level, int
  optname, void optval, socklen_t optlen)
• Int setsockopt(int sockfd, int level, int
  optname, const void optval, socklen_t optlen)
• Level includes general socket option (SOL_SOCKET)
  and protocol-specific option (IP, TCP, etc).
• Option value can be of different types int,
  in_addr, timeval, ---- that is why we use the
  void pointer.

3

• General socket options (level SOL_SOCKET)
• Optnames
• SO_BROADCAST(int) permit sending broadcast
  datagram
• SO_DEBUG for debugging purpose
• SO_DONROUTE used by routing daemon to make sure
  a packet goes through a certain interface.
• SO_ERROR can only be got (not set), reset the
  error
• SO_KEEPALIVE for TCP only, automatic send
  keepalive message when inactive for 2 hours (can
  be modified).
• SO_LINGER for TCP only, determines the behavior
  when a close is called.
• SO_OOBINLINE put out of band data in the normal
  input queue.
• SO_RCVBUF, SO_SNDBUF send and receive buffer
  size.

4

• General socket options (level SOL_SOCKET)
• Optnames
• SO_RCVLOWAT, SO_SENDLOWAT low watermark affect
  the select system call
• SO_RCVTIMEO, SO_SNDTIMEO inherent timeout time
  (disable by default)
• SO_REUSEADDR Allows the port to be reused all
  server should do this to be restart immediately
• SO_TYPE socket type? SOCK_STREAM and SOCK_DGRAM.
• SO_USELOOPBACK sending socket gets a copy?

5

• IP options
• Allows packets sent through a socket to have
  certain behavior, e.g source routing
• Level IPPROTO_IP
• Optnames (manipulating IP header fields)
• IP_HDRINCL
• IP_OPTIONS
• IP_RECVDSTADDR
• IP_RECVIF
• IP_TOS
• IP_TTL

6

• IP options
• Level IPPROTO_IP
• Optnames (IP MULTICAST related)
• IP_MULTICAST_IF
• IP_MULTICAST_TTL
• IP_MULTICAST_LOOP
• IP_ADD_MEMBERSHIP
• IP_DROP_MEMBERSHIP

7

• TCP options
• Level IPPROTO_TCP
• Optnames
• TCP_KEEPALIVE set the time
• TCP_MAXRT maximum retransmission time
• TCP_MAXSEG maximum segment size
• TCP_NODELAY wait to ack or not (enable)
• TCP_STDURG where is the urgent pointer.
• See example1.c