Socket option Getsockopt ou setsockopt fcntl ioctl

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

Options

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.

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

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

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

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

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

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

SO_KEEPALIVE

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

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

SO_LINGER

 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);

SO_LINGER

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

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 bytes  UDP send buffer 9000 bytes and UDP receive buffer 40000

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

Bandwidth – delay product Bandwidth – Delay product – amount of byte in the pipe Transmission rate x RTT For instance: T1 ( 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)

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

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

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

SO_REUSEPORT SO_REUSEADDR is equivalent to SO_REUSEPORT when multicast is used

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

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

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

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

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

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

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

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

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

Opções TCP

TCP_STDURG – changes interpretation of the urgent pointer field