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<p>
</blockquote><h4>OPTION FOR DATAGRAM SOCKETS</h4><blockquote><p>
The following section discusses an option for datagram (UDP) sockets.
<p>
</blockQuote><h4>SO_BROADCAST -- Sending to Multiple Destinations</h4><blockQuote>
Specify the <b>SO_BROADCAST</b> option when an application needs to send
data to more than one destination:
<pre>    setsockopt (sock, SOL_SOCKET, SO_BROADCAST, &amp;optval, sizeof (optval));
</pre>
The value at <i>optval</i> is an integer (type <i>int</i>), either 1 (on) or 0
(off).
<p>
</blockquote><h4>OPTIONS FOR DATAGRAM AND RAW SOCKETS</h4><blockquote><p>
The following section discusses options for multicasting on UDP and RAW
sockets.
<p>
</blockQuote><h4>IP_ADD_MEMBERSHIP -- Join a Multicast Group</h4><blockQuote>
Specify the <b>IP_ADD_MEMBERSHIP</b> option when a process needs to join
multicast group:
<pre>    setsockopt (sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char *)&amp;ipMreq,
                sizeof (ipMreq));
</pre>
The value of <i>ipMreq</i> is an <b>ip_mreq</b> structure. 
<b>ipMreq.imr_multiaddr.s</b>_addr</b> is the internet multicast address
<b>ipMreq.imr_interface.s</b>_addr</b> is the internet unicast address of the 
interface through which the multicast packet needs to pass.
<p>
</blockQuote><h4>IP_DROP_MEMBERSHIP -- Leave a Multicast Group</h4><blockQuote>
Specify the <b>IP_DROP_MEMBERSHIP</b> option when a process needs to leave
a previously joined multicast group:
<pre>    setsockopt (sock, IPPROTO_IP, IP_DROP_MEMBERSHIP, (char *)&amp;ipMreq,
                sizeof (ipMreq));
</pre>
The value of <i>ipMreq</i> is an <b>ip_mreq</b> structure.  
<b>ipMreq.imr_multiaddr.s</b>_addr</b> is the internet multicast address.
<b>ipMreq.imr_interface.s</b>_addr</b> is the internet unicast address of the 
interface to which the multicast address was bound.
<p>
</blockQuote><h4>IP_MULTICAST_IF -- Select a Default Interface for Outgoing Multicasts</h4><blockQuote>
Specify the <b>IP_MULTICAST_IF</b> option when an application needs to specify
an outgoing network interface through which all multicast packets
are sent:
<pre>    setsockopt (sock, IPPROTO_IP, IP_MULTICAST_IF, (char *)&amp;ifAddr,
                sizeof (mCastAddr));
</pre>
The value of <i>ifAddr</i> is an <b>in_addr</b> structure.  
<b>ifAddr.s</b>_addr</b> is the internet network interface address.
<p>
</blockQuote><h4>IP_MULTICAST_TTL -- Select a Default TTL</h4><blockQuote>
Specify the <b>IP_MULTICAST_TTL</b> option when an application needs to select
a default TTL (time to live) for outgoing multicast
packets:
<p>
<pre>    setsockopt (sock, IPPROTO_IP, IP_MULTICAST_TTL, &amp;optval, sizeof(optval));
</pre>
The value at <i>optval</i> is an integer (type <i>int</i>), time to live value.
<p>
<table>
<tr valign=top>
<th align=left>optval(TTL)  </th><th align=left>  Application                   </th><th align=left> Scope</tr>
<tr><td colspan="3"><hr></tr>
<tr valign=top>
<td align=left>0            </td><td align=left>                                </td><td align=left> same interface</tr>
<tr valign=top>
<td align=left>1            </td><td align=left>                                </td><td align=left> same subnet</tr>
<tr valign=top>
<td align=left>31           </td><td align=left> local event video              </td><td align=left> </tr>
<tr valign=top>
<td align=left>32           </td><td align=left>                                </td><td align=left> same site</tr>
<tr valign=top>
<td align=left>63           </td><td align=left> local event audio              </td><td align=left> </tr>
<tr valign=top>
<td align=left>64           </td><td align=left>                                </td><td align=left> same region</tr>
<tr valign=top>
<td align=left>95           </td><td align=left> IETF channel 2 video           </td><td align=left> </tr>
<tr valign=top>
<td align=left>127          </td><td align=left> IETF channel 1 video           </td><td align=left> </tr>
<tr valign=top>
<td align=left>128          </td><td align=left>                                </td><td align=left> same continent</tr>
<tr valign=top>
<td align=left>159          </td><td align=left> IETF channel 2 audio           </td><td align=left> </tr>
<tr valign=top>
<td align=left>191          </td><td align=left> IETF channel 1 audio           </td><td align=left> </tr>
<tr valign=top>
<td align=left>223          </td><td align=left> IETF channel 2 low-rate audio  </td><td align=left> </tr>
<tr valign=top>
<td align=left>255          </td><td align=left> IETF channel 1 low-rate audio  </td><td align=left></tr>
<tr valign=top>
<td align=left>             </td><td align=left> unrestricted in scope          </td><td align=left></tr>
<tr valign=top>
<td align=left></tr>
</tr>

</table>

</blockQuote><h4>IP_MULTICAST_LOOP -- Enable or Disable Loopback</h4><blockQuote>
Enable or disable loopback of outgoing multicasts.
<pre>    setsockopt (sock, IPPROTO_IP, IP_MULTICAST_LOOP, &amp;optval, sizeof(optval));
</pre>
The value at <i>optval</i> is an integer (type <i>int</i>), either 1(on) or 0
(off).
<p>
</blockquote><h4>OPTIONS FOR BOTH STREAM AND DATAGRAM SOCKETS</h4><blockquote><p>
The following sections describe options that can be used with either
stream or datagram sockets.
<p>
</blockQuote><h4>SO_REUSEADDR -- Reusing a Socket Address</h4><blockQuote>
Specify the <b>SO_REUSEADDR</b> option to bind a stream socket to a local
port that may be still bound to another stream socket:
<pre>    setsockopt (sock, SOL_SOCKET, SO_REUSEADDR, &amp;optval, sizeof (optval));
</pre>
The value at <i>optval</i> is an integer (type <i>int</i>), either 1 (on) or 0
(off).
<p>
When the <b>SO_REUSEADDR</b> option is turned on, applications may bind a
stream socket to a local port even if it is still bound to another
stream socket, if that other socket is associated with a "zombie" protocol
control block context not yet freed from previous sessions.  The
uniqueness of port number combinations for each connection is still
preserved through sanity checks performed at actual connection
setup time.  If this option is not turned on and an application
attempts to bind to a port which is being used by a zombie protocol
control block, the <b><i><a href="./sockLib.html#bind">bind</a></i>(&nbsp;)</b> call fails.
<p>
</blockQuote><h4>SO_SNDBUF -- Specifying the Size of the Send Buffer</h4><blockQuote>
Specify the <b>SO_SNDBUF</b> option to adjust the maximum size of the
socket-level send buffer:
<pre>    setsockopt (sock, SOL_SOCKET, SO_SNDBUF, &amp;optval, sizeof (optval));
</pre>
The value at <i>optval</i> is an integer (type <b>int</b>) that specifies the
size of the socket-level send buffer to be allocated.
<p>
When stream or datagram sockets are created, each transport protocol
reserves a set amount of space at the socket level for use when the
sockets are attached to a protocol.  For TCP, the default size of
the send buffer is 8192 bytes.  For UDP, the default size of the
send buffer is 9216 bytes.  Socket-level buffers are allocated
dynamically from the mbuf pool.
<p>
The effect of setting the maximum size of buffers (for both
<b>SO_SNDBUF</b> and <b>SO_RCVBUF</b>, described below) is not actually to
allocate the mbufs from the mbuf pool, but to set the high-water
mark in the protocol data structure which is used later to limit the
amount of mbuf allocation.  Thus, the maximum size specified for the
socket level send and receive buffers can affect the performance of
bulk data transfers.  For example, the size of the TCP receive
windows is limited by the remaining socket-level buffer space.
These parameters must be adjusted to produce the optimal result for
a given application.
<p>
</blockQuote><h4>SO_RCVBUF -- Specifying the Size of the Receive Buffer</h4><blockQuote>
Specify the <b>SO_RCVBUF</b> option to adjust the maximum size of the
socket-level receive buffer:
<pre>    setsockopt (sock, SOL_SOCKET, SO_RCVBUF, &amp;optval, sizeof (optval));
</pre>
The value at <i>optval</i> is an integer (type <b>int</b>) that specifies the
size of the socket-level receive buffer to be allocated.
<p>
When stream or datagram sockets are created, each transport protocol
reserves a set amount of space at the socket level for use when the
sockets are attached to a protocol.  For TCP, the default size is
8192 bytes.  UDP reserves 41600 bytes, enough space for up to forty
incoming datagrams (1 Kbyte each).
<p>
See the <b>SO_SNDBUF</b> discussion above for a discussion of the impact of
buffer size on application performance.
<p>
</blockQuote><h4>SO_OOBINLINE -- Placing Urgent Data in the Normal Data Stream</h4><blockQuote>
Specify the <b>SO_OOBINLINE</b> option to place urgent data within the
normal receive data stream:
<pre>    setsockopt (sock, SOL_SOCKET, SO_OOBINLINE, &amp;optval, sizeof (optval));
</pre>
TCP provides an expedited data service which does not conform to the
normal constraints of sequencing and flow control of data
streams. The expedited service delivers "out-of-band" (urgent) data
ahead of other "normal" data to provide interrupt-like services (for
example, when you hit a CTRL-C during telnet or rlogin session while
data is being displayed on the screen.)
<p>
TCP does not actually maintain a separate stream to support the
urgent data.  Instead, urgent data delivery is implemented as a
pointer (in the TCP header) which points to the sequence number of
the octet following the urgent data. If more than one transmission
of urgent data is received from the peer, they are all put into the
normal stream. This is intended for applications that cannot afford
to miss out on any urgent data but are usually too slow to respond
to them promptly.
<p>
</blockquote><h4>RETURNS</h4><blockquote><p>
<p>
OK, or ERROR if there is an invalid socket, an unknown option, an option
length greater than MLEN, insufficient mbufs, or the call is unable to set
the specified option.
</blockquote><h4>SEE ALSO</h4><blockquote><p>
<b><a href="./sockLib.html#top">sockLib</a></b>

<hr>
<a name="getsockopt"></a>
<p align=right>
<a href="rtnIndex.html"><i>Libraries :  Routines</i></a></p>

</blockquote><h1><i>getsockopt</i>(&nbsp;)</h1> <blockquote></a></blockquote><h4>NAME</h4><blockquote>  
<p><strong><i>getsockopt</i>(&nbsp;)</strong> - get socket options</p>

</blockquote><h4>SYNOPSIS</h4><blockquote><p>
<pre>STATUS getsockopt
    (
    int    s,       /* socket */
    int    level,   /* protocol level for options */
    int    optname, /* name of option */
    char * optval,  /* where to put option */
    int *  optlen   /* where to put option length */
    )</pre>

</blockquote><h4>DESCRIPTION</h4><blockquote><p>
This routine returns relevant option values associated with a socket.
To manipulate options at the "socket" level, <i>level</i> should be <b>SOL_SOCKET</b>.
Any other levels should use the appropriate protocol number.
The parameter <i>optlen</i> should be initialized to indicate the amount of
space referenced by <i>optval</i>.  On return, the value of the option is copied to
<i>optval</i> and the actual size of the option is copied to <i>optlen</i>.
<p>
Although <i>optval</i> is passed as a char *, the actual variable whose address 
gets passed in should be an integer or a structure, depending on which 
<i>optname</i> is being passed. Refer to <b><i><a href="./sockLib.html#setsockopt">setsockopt</a></i>(&nbsp;)</b> to determine the correct 
type of the actual variable (whose address should then be cast to a char *).
<p>
</blockquote><h4>RETURNS</h4><blockquote><p>
<p>
OK, or ERROR if there is an invalid socket, an unknown option, or the call
is unable to get the specified option.
<p>
</blockquote><h4>EXAMPLE</h4><blockquote><p>
Because <b>SO_REUSEADDR</b> has an integer parameter, the variable to be
passed to <b><i><a href="./sockLib.html#getsockopt">getsockopt</a></i>(&nbsp;)</b> should be declared as
<pre>   int reuseVal;
</pre>
and passed in as 
<pre>   (char *)&amp;reuseVal.
</pre>
Otherwise the user might mistakenly declare <b>reuseVal</b> as a character,
in which case <b><i><a href="./sockLib.html#getsockopt">getsockopt</a></i>(&nbsp;)</b> will only return the first byte of the
integer representing the state of this option.  Then whether the return
value is correct or always 0 depends on the endian-ness of the machine.
<p>
</blockquote><h4>SEE ALSO</h4><blockquote><p>
<b><a href="./sockLib.html#top">sockLib</a></b>, <b><i><a href="./sockLib.html#setsockopt">setsockopt</a></i>(&nbsp;)</b>

<hr>
<a name="getsockname"></a>
<p align=right>
<a href="rtnIndex.html"><i>Libraries :  Routines</i></a></p>

</blockquote><h1><i>getsockname</i>(&nbsp;)</h1> <blockquote></a></blockquote><h4>NAME</h4><blockquote>  
<p><strong><i>getsockname</i>(&nbsp;)</strong> - get a socket name</p>

</blockquote><h4>SYNOPSIS</h4><blockquote><p>
<pre>STATUS getsockname
    (
    int               s,      /* socket descriptor */
    struct sockaddr * name,   /* where to return name */
    int *             namelen /* space available in name, later filled in */
                              /* actual name size */
    )</pre>

</blockquote><h4>DESCRIPTION</h4><blockquote><p>
This routine gets the current name for the specified socket <i>s</i>.
The parameter <i>namelen</i> should be initialized to indicate the amount of
space referenced by <i>name</i>.  On return, the name of the socket is copied to
<i>name</i> and the actual size of the socket name is copied to <i>namelen</i>.
<p>
</blockquote><h4>RETURNS</h4><blockquote><p>
OK, or ERROR if the socket is invalid
or not connected.
</blockquote><h4>SEE ALSO</h4><blockquote><p>
<b><a href="./sockLib.html#top">sockLib</a></b>

<hr>
<a name="getpeername"></a>
<p align=right>
<a href="rtnIndex.html"><i>Libraries :  Routines</i></a></p>

</blockquote><h1><i>getpeername</i>(&nbsp;)</h1> <blockquote></a></blockquote><h4>NAME</h4><blockquote>  
<p><strong><i>getpeername</i>(&nbsp;)</strong> - get the name of a connected peer</p>

</blockquote><h4>SYNOPSIS</h4><blockquote><p>
<pre>STATUS getpeername
    (
    int               s,      /* socket descriptor */
    struct sockaddr * name,   /* where to put name */
    int *             namelen /* space available in name, later filled in */
                              /* actual name size */
    )</pre>

</blockquote><h4>DESCRIPTION</h4><blockquote><p>
This routine gets the name of the peer connected to socket <i>s</i>.
The parameter <i>namelen</i> should be initialized to indicate the amount of
space referenced by <i>name</i>.  On return, the name of the socket is copied to
<i>name</i> and the actual size of the socket name is copied to <i>namelen</i>.
<p>
</blockquote><h4>RETURNS</h4><blockquote><p>
OK, or ERROR if the socket is invalid
or not connected.
</blockquote><h4>SEE ALSO</h4><blockquote><p>
<b><a href="./sockLib.html#top">sockLib</a></b>

<hr>
<a name="shutdown"></a>
<p align=right>
<a href="rtnIndex.html"><i>Libraries :  Routines</i></a></p>

</blockquote><h1><i>shutdown</i>(&nbsp;)</h1> <blockquote></a></blockquote><h4>NAME</h4><blockquote>  
<p><strong><i>shutdown</i>(&nbsp;)</strong> - shut down a network connection</p>

</blockquote><h4>SYNOPSIS</h4><blockquote><p>
<pre>STATUS shutdown
    (
    int s,  /* socket to shut down */
    int how /* 0 = receives disallowed 1 = sends disallowed 2 = sends and */
            /* disallowed */
    )</pre>

</blockquote><h4>DESCRIPTION</h4><blockquote><p>
This routine shuts down all, or part, of a connection-based socket <i>s</i>.
If the value of <i>how</i> is 0, receives are disallowed.  If <i>how</i> is 1,
sends are disallowed.  If <i>how</i> is 2, both sends and receives are
disallowed.
<p>
</blockquote><h4>RETURNS</h4><blockquote><p>
OK, or ERROR if the socket is invalid or not connected.
</blockquote><h4>SEE ALSO</h4><blockquote><p>
<b><a href="./sockLib.html#top">sockLib</a></b>

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