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NAME    [Toc]    [Back]

     rtalloc, rtalloc_ign, rtalloc1 -- look up a route in the kernel routing

SYNOPSIS    [Toc]    [Back]

     #include <sys/types.h>
     #include <sys/socket.h>
     #include <net/route.h>

     rtalloc(struct route *ro);

     rtalloc_ign(struct route *ro, u_long flags);

     struct rtentry *
     rtalloc1(struct sockaddr *sa, int report, u_long flags);

DESCRIPTION    [Toc]    [Back]

     The kernel uses a radix tree structure to manage routes for the networking
 subsystem.  The rtalloc() family of routines is used by protocols to
     query this structure for a route corresponding to a particular end-node
     address, and to cause certain protocol- and interface-specific actions to
     take place.

     When a route with the flag RTF_CLONING or RTF_PRCLONING is retrieved, and
     the action of those flags is not masked, the rtalloc facility automatically
 generates a new route using information in the old route as a template,
 and in the case of RTF_CLONING, sends an RTM_RESOLVE message to
     the appropriate interface-address route-management routine
     (ifa->ifa_rtrequest()).  RTF_PRCLONING routes are assumed to be managed
     by the protocol family and no resolution requests are made, but all
     routes generated by the cloning process retain a reference to the route
     from which they were generated.  If the RTF_XRESOLVE flag is set, then
     the RTM_RESOLVE message is sent instead on the route(4) socket interface,
     requesting that an external program resolve the address in question and
     modify the route appropriately.

     The default interface is rtalloc().  Its only argument is ro, a pointer
     to a ``struct route'', which is defined as follows:

	   struct route {
		   struct sockaddr ro_dst;
		   struct rtentry *ro_rt;
     Thus, this function can only be used for address families which are
     smaller than the default ``struct sockaddr''.  Before calling rtalloc()
     for the first time, callers should ensure that unused bits of the structure
 are set to zero.  On subsequent calls, rtalloc() returns without
     performing a lookup if ro->ro_rt is non-null and the RTF_UP flag is set
     in the route's rt_flags field.

     The rtalloc_ign() interface can be used when the default actions of
     rtalloc() in the presence of the RTF_CLONING and RTF_PRCLONING flags are
     undesired.  The ro argument is the same as rtalloc(), but there is additionally
 a flags argument, which lists the flags in the route which are
     to be ignored (ordinarily, one or both of RTF_CLONING or RTF_PRCLONING).

     The rtalloc1() function is the most general form of rtalloc() (and both
     of the other forms are implemented as calls to rtalloc1).	It does not
     use the ``struct route'', and is therefore suitable for address families
     which require more space than is in a traditional ``struct sockaddr''.
     Instead, it takes a ``struct sockaddr *'' directly as the sa argument.
     The second argument, report, controls whether RTM_RESOLVE requests are
     sent to the lower layers when an RTF_CLONING or RTF_PRCLONING route is
     cloned.  Ordinarily a value of one should be passed, except in the processing
 of those lower layers which use the cloning facility.  The third
     argument, flags, is a set of flags to ignore, as in rtalloc_ign().

RETURN VALUES    [Toc]    [Back]

     The rtalloc() and rtalloc_ign() functions do not return a value.  The
     rtalloc1() function returns a pointer to a routing-table entry if it succeeds,
 otherwise a null pointer.  Lack of a route should in most cases be
     translated to the errno(2) value EHOSTUNREACH.

SEE ALSO    [Toc]    [Back]

     route(4), rtentry(9)

HISTORY    [Toc]    [Back]

     The rtalloc facility first appeared in 4.2BSD, although with much different
 internals.  The rtalloc_ign() function and the flags argument to
     rtalloc1() first appeared in FreeBSD 2.0.

AUTHORS    [Toc]    [Back]

     This manual page was written by Garrett Wollman, as were the changes to
     implement RTF_PRCLONING and the rtalloc_ign() function and the flags
     argument to rtalloc1().

FreeBSD 5.2.1			October 8, 1996 		 FreeBSD 5.2.1
[ Back ]
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