1. Advanced UNIX programming
Fall 2002
Instructor: Ashok Srinivasan
Lecture 23
Acknowledgements: The syllabus and power point presentations are modified versions of those by T. Baker and X. Yuan

2. Announcements Reading assignment Chapter 7 Chapter 8
Sections 7.1 – 7.6 and 7.9 – 7.11
Chapter 8
Midterm next Monday

3. Week 9 Topics Socket options Introduction to UDP
getsockopt, setsockopt
fcntl
ioctl
Introduction to UDP
TCP vs UDP
UDP interface

4. Socket options getsockopt, setsockopt fcntl ioctl
General socket options
IP options
TCP options
fcntl
ioctl

5. getsockopt, setsockopt
#include <sys/socket.h>
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);
The level includes general socket options (SOL_SOCKET) and protocol-specific options (for IP, TCP, etc).
Option value can be of different types: pointers to int, in_addr, timeval, etc

6. General socket options
level = SOL_SOCKET, optnames =
SO_BROADCAST
Permit sending broadcast datagram
SO_KEEPALIVE
For TCP only, automatically send a keepalive message when inactive for 2 hours (can be modified)
SO_LINGER
for TCP only, determines behavior on close
SO_RCVBUF, SO_SNDBUF
Send and receive buffer size

7. General socket options (continued)
level = SOL_SOCKET, optnames =
SO_RCVLOWAT, SO_SENDLOWAT
low watermark – affects the select system call
SO_RCVTIMEO, SO_SNDTIMEO
Inherent timeout time (disabled by default)
SO_TYPE
Socket type: SOCK_STREAM and SOCK_DGRAM
Etc.

8. IP options
Allows packets sent through a socket to have certain behavior
For example, source routing
level = IPPROTO_IP
optname (manipulating IP header fields)
IP_OPTIONS
IP_RECVDSTADDR
IP_RECVIF
IP_TOS
IP_TTL
Etc.

9. level = IPPROTO_TCP, optname =
TCP options
level = IPPROTO_TCP, optname =
TCP_KEEPALIVE
Set the time
TCP_MAXRT
Maximum retransmission time
TCP_MAXSEG
Maximum segment size
See example1.c

10. fcntl and ioctl fcntl ioctl File control on open files
Set file descriptor flags (FD_CLOEXEC)
Non-blocking mode, etc.
ioctl
Some I/O control operations