1. Socket option Getsockopt ou setsockopt fcntl ioctl

2. Socket option #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); Both return: 0 if OK,–1 on error Level – code in the system to interpret the option Optval – pointer to a variable from which the new value of the option is fetched by setsocopt or into which the current value of the option is stored

3. Options

5. Socket options Options inherited by a connected TCP socket from the listening socket  SO_DEBUG;  SO_DONTROUTE;  SO_KEEPALIVE;  SO_LINGER;  SO_OOBINLINE;  SO_RCVBUF;  SO_SNDBUF.

6. SO_BROADCAST Enables/disable the ability to send broadcast messages Only for networks that allow broadcast Code EACCESS returned

7. SO_DEBUG Valid for TCP Keeps track of all segment sent and received by TCP, kept on a circular buffer which can be examined by the kernel using the trpt function

8. SO_DONTROUTE Used to bypass the routing mechanism For UDP sockets, can set flag MSG_DONTROUTE when using send, sento, sendmsg Used by routing daemons to ignore the content of routing tables

9. SO_ERROR Used to retrieve error code Blocked process is notified via a select or a signal driven I/O

10. SO_KEEPALIVE If option is set TCP send automatically a keepalive message every two hours without exchanging data across the socket. What can happen:  TCP peer sends an ACK. The applications is not notified;  TCP peer sends na RST. Socket is closed and the error message ECONNRESET is returned.  If no response is given, at most eight messages are sent, one every 75 seconds. After that an error code ETIMEDOUT is sent

11. SO_KEEPALIVE (cont.):  If an ICMP message “host unreachable” is recieved, it is passed to the application  The duration of the interval to send the keepalive message can be altered to all sockets  Used in servers

12. SO_KEEPALIVE

13. SO_LINGER By default, close send data in buffer and returns immediately. So-linger allows change this way of operation struct linger { int l_onoff; /* 0=off, nonzero=on */ int l_linger; /* linger time (seconds) */ }; l_onoff is zero, option is turned off close is called. Option is ignored l_onoff is nonzsero and l_linger = zero buffer content is discarded and connection is discarded, an RST is sent to the peer, avoids time-wait

14. SO_LINGER l_onoff non zero, l_linger non zero – process is put to sleep until all data in buffer is sent and acked or linger period expires The expiration of lingertime can be checked

15. SO_LINGER

18.  Application level ack  Client: char ack; Write(sockfd, data, nbytes); n = Read(sockfd, &ack, 1);  Server: nbytes = Read(sockfd, buff, sizeof(buff)); Write(sockfd, "", 1);

19. SO_LINGER

21. SO_OOBINLINE Out-of-band data is put in the normal buffer queue

22. SO_RCVBUF e SO_SNDBUF Set value for the size of send buffer and receive buffer Default values  TCP old versions: 4096 bytes  TCP current versions: 8192 a 61440 bytes  UDP send buffer 9000 bytes and UDP receive buffer 40000

23. SO_RCVBUF e SO_SNDBUF The size of the buffer needs to be set before connect is called at the client and before listen is called at the server in the server A atribuição do tamanho do buffer deve ser feita no cliente antes de chamar connect e no servidor antes de chamar listen At least 3 MSS is recommended

24. Bandwidth – delay product Bandwidth – Delay product – amount of byte in the pipe Transmission rate x RTT For instance: T1 (1.536.000 bytes/sec) with an RTT of 60ms, bandwidth-delay product = 11,520 bytes If buffer is smaller than bandwidth-delay product TCP becomes the bottleneck Need larger buffers for high speed networks or networks with long propagation delays (satellite networks)

25. SO_RCVLOWAT e SO_SNDLOWAT Changes the low-water mark of the buffer Minimum amount of data required by select to consider data as either read or written

26. SO_REUSEADDR Allows server to perform bind on a port even if it is being used by another process (typically connected socket derived from a listening sockets) Allows multiple instances of the same server to be started on the same port as each instance binds a different local IP address

27. SO_REUSEADDR Allows a single process to bind the same port to multiple sockets, as long as each bind specifies a different local IP Allows completely duplicated bindings: a bind of an IP address and port when the same IP address and port are already bound to another socket. Useful for multicast when the socket option SO_REUSEPORT is not available

28. SO_REUSEPORT SO_REUSEADDR is equivalent to SO_REUSEPORT when multicast is used

29. SO_TYPE e SO_USELOOPBACK SO_TYPE: returns the socket type SO_USELOOPBACK: receives copy of all transmitted

30. IPv4 Options Level IPROTO_IP IP_HDRINCL – allows writing to IP header – used in RAW_SOCKET (ICMP) What cannot be attributed  Checksum  IP identification field  Output interface INADDR_V4  Implementation dependent option

31. IPv4 Options IP_options – allow setting of IP datagram fields IP_RECVDSTADDR – allow to return a UDP packet as ancillary data (control) by using recvmsg IP_TOS – allow setting field ToS

32. IPv4 Options IP_TTL – allow writing and reading to filed Time to Live (TTL). Default = 64

33. IPv6 Options LEVEL IPTPROTO_IPv6 IPv6_ADDRFOMR – allows converting an IPv4 socket to an IPv6 socket IPv6 checksum – computes and store checksum for outgoing packets and verify checksum for incoming packets. Parameter indicates where checksum field is located

34. IPv6 Options IPv6_DSTOPTS – specifies that any received IPv6 destination option are to be returned as ancillary data by recvmsg IPv6_HOPLIMIT – specifies that the received hop limit field to be returned as ancillary data by recvmsg IPv6_HOPOPTS – specifies that the option hop-by-hop has to be returned as ancillary by recvmsg IPv6_NEXTHOP – specifies the next hop a packet should go

35. IPv6 Options IPv6_PKTINFO – specifies that destination address and interface are to be returned as ancillary data IPv6_RTHDR – specifies that the routing fileds of the header should be returned as ancillary data by rcvmsg IPv6-UNICAST_HOPS – set thehop limit

36. ICMPv6 Level IPROTO_ICMPv6 ICMP6_FILTER – specifies which of the 256 ICMPv6 messages can be sent on a podem RAWSOCKET

37. Opções TCP TCP_KEEPALIVE – specifies the time interval in seconds that the connection should send keepalive messages TCP_MAXSEG – allows setting and retrieving value of MSS TCP_NODELAY – disable Nagle’s algorithm which prevents small packets to be sent. Small segments are sent in case there are pending acks

38. Opções TCP

40. TCP_STDURG – changes interpretation of the urgent pointer field