1. IPv4 socket option Level => IPPROTO_IP
IP_HDRINCL => If this option is set for a raw IP socket, we must build our IP header for all the datagrams that we send on the raw socket.(chapter 26)

2. IP_OPTIONS=>allows us to set IP option in IPv4 header.(chapter 24)
IP_RECVDSTADDR=>This socket option causes the destination IP address of a received UDP datagram to be returned as ancillary data by recvmsg.(chapter20)

3. IP_RECVIF
Cause the index of the interface on which a UDP datagram is received to be returned as ancillary data by recvmsg.(chapter20)

4. IP_TOS
lets us set the type-of-service(TOS) field in IP header for a TCP or UDP socket.
If we call getsockopt for this option, the current value that would be placed into the TOS(type of service) field in the IP header is returned.(figure A.1)

5. IP_TTL
We can set and fetch the default TTL(time to live field, figure A.1).

6. ICMPv6 socket option
This socket option is processed by ICMPv6 and has a level of IPPROTO_ICMPV6.
ICMP6_FILTER =>lets us fetch and set an icmp6_filter structure that specifies which of the 256possible ICMPv6 message types are passed to the process on a raw socket.(chapter 25)

7. IPv6 socket option
This socket option is processed by IPv6 and have a level of IPPROTO_IPV6.
IPV6_ADDRFORM=>allow a socket to be converted from IPv4 to IPv6 or vice versa.(chapter 10)
IPV6_CHECKSUM=>specifies the byte offset into the user data of where the checksum field is located.

8. IPV6_DSTOPTS
Specifies that any received IPv6 destination options are to be returned as ancillary data by recvmsg.

9. IPV6_HOPLIMIT
Setting this option specifies that the received hop limit field be returned as ancillary data by recvmsg.(chapter 20)
Default off.

10. IPV6_HOPOPTS
Setting this option specifies that any received IPv6 hop-by-hop option are to be returned as ancillary data by recvmsg.(chapter 24)

11. IPV6_NEXTHOP
This is not a socket option but the type of an ancillary data object that can be specified to sendmsg. This object specifies the next-hop address for a datagram as a socket address structure.(chapter20)

12. IPV6_PKTINFO
Setting this option specifies that the following two pieces of infoemation about a received IPv6 datagram are to be returned as ancillary data by recvmsg:the destination IPv6 address and the arriving interface index.(chapter 20)

13. IPV6_PKTOPTIONS
Most of the IPv6 socket options assume a UDP socket with the information being passed between the kernel and the application using ancillary data with recvmsg and sendmsg.
A TCP socket fetch and store these values using IPV6_ PKTOPTIONS socket option.

14. IPV6_RTHDR
Setting this option specifies that a received IPv6 routing header is to be returned as ancillary data by recvmsg.(chapter 24)
Default off

15. IPV6_UNICAST_HOPS This is similar to the IPv4 IP_TTL.
Specifies the default hop limit for outgoing datagram sent on the socket, while fetching the socket option returns the value for the hop limit that the kernel will use for the socket.

16. TCP socket option
There are five socket option for TCP, but three are new with Posix.1g and not widely supported.
Specify the level as IPPROTO_TCP.

17. TCP_KEEPALIVE This is new with Posix.1g
It specifies the idle time in second for the connection before TCP starts sending keepalive probe.
Default 2hours
this option is effective only when the SO_KEEPALIVE socket option enabled.

18. TCP_MAXRT This is new with Posix.1g.
It specifies the amount of time in seconds before a connection is broken once TCP starts retransmitting data.
0 : use default
-1:retransmit forever
positive value:rounded up to next transmission time

19. TCP_MAXSEG
This allows us to fetch or set the maximum segment size(MSS) for TCP connection.

20. TCP_NODELAY purpose of the Nagle algorithm.
This option disables TCP’s Nagle algorithm.
(default this algorithm enabled)
purpose of the Nagle algorithm.
==>prevent a connection from having multiple small packets outstanding at any time.
Small packet => any packet smaller than MSS.

21. Nagle algorithm Default enabled.
Reduce the number of small packet on the WAN.
If given connection has outstanding data , then no small packet data will be sent on connection until the existing data is acknowledged.

22. Nagle algorithm disablede
250 l
500 l
750 o
1000 !
1250
1500
1500
1750
2000

23. Nagle algorithm enablede
250 l
500 el l
750 o
1000 !
1250 lo
1500
1500
1750 !
2000
2250
2500

24. fcntl function File control
This function perform various descriptor control operation.
Provide the following features
Nonblocking I/O(chapter 15)
signal-driven I/O(chapter 22)
set socket owner to receive SIGIO signal.
(chapter 21,22)

25. #include <fcntl.h> int fcntl(int fd, int cmd, …./* int arg */);
Returns:depends on cmd if OK, -1 on error
O_NONBLOCK : nonblocking I/O
O_ASYNC : signal driven I/O notification

26. Nonblocking I/O using fcntl
Int flags;
/* set socket nonblocking */
if((flags = fcntl(fd, f_GETFL, 0)) < 0)
err_sys(“F_GETFL error”);
flags |= O_NONBLOCK;
if(fcntl(fd, F_SETFL, flags) < 0)
err_sys(“F_ SETFL error”);
each descriptor has a set of file flags that fetched with
the F_GETFL command
and set with F_SETFL command.

27. Misuse of fcntl /* wrong way to set socket nonblocking */
if(fcntl(fd, F_SETFL,O_NONBLOCK) < 0)
err_sys(“F_ SETFL error”);
/* because it also clears all the other file status flags.*/

28. Turn off the nonblocking flag
Flags &= ~O_NONBLOCK;
if(fcntl(fd, F_SETFL, flags) < 0)
err_sys(“F_SETFL error”);

29. F_SETOWN
The integer arg value can be either positive(process ID) or negative (group ID)value to receive the signal.
F_GETOWN => retrurn the socket owner by fcntl function, either process ID or process group ID.