1. Socket options: a summary –Tcp options, ip options and general socket options can be examined and sometimes modified. getsockopt, setsockopt routines Some examples: –Socket (TCP/UDP) send/receive buffer size –Socket (TCP/UDP) send/receive low/high watermark –UDP broadcasting –TCP keep alive timer –IP options: e.g. source routing »IP Time to live (TTL) »IP quality of service (TOS) –IP multicast options

2. –#include 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 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 Example optnames: (manipulating IP header fields) –IP_HDRINCL: who builds the IP header (raw socket). –IP_OPTIONS: setting IP optional header fields –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) –See example5.c