ARP(9)                 NetBSD Kernel Developer's Manual                 ARP(9)

NAME
     arp, arp_ifinit, arpresolve, arpintr -- externally visible ARP functions

SYNOPSIS
     #include <netinet/if_inarp.h>

     void
     arp_ifinit(struct ifnet *ifp, struct ifaddr *ifa);

     int
     arpresolve(struct ifnet *ifp, struct rtentry *rt, struct mbuf *m,
         struct sockaddr *dst, u_char *desten);

     void
     arpintr();

DESCRIPTION
     The arp functions provide the interface between the arp module and the
     network drivers which need arp functionality.  Such drivers must request
     the arp attribute in their "files" declaration.

     arp_ifinit()  Sets up the arp specific fields in ifa.  Additionally, it
                   sends out a gratuitous arp request on ifp, so that other
                   machines are warned that we have a (new) address and dupli-
                   cate addresses can be detected.

                   You must call this in your drivers' ioctl function when you
                   get a SIOCSIFADDR request with an AF_INET address family.

     arpresolve()  is called by network output functions to resolve an IPv4
                   address.  If no rt is given, a new one is looked up or cre-
                   ated.  If the passed or found rt does not contain a valid
                   gateway link level address, a pointer to the packet in m is
                   stored in the route entry, possibly replacing older stored
                   packets, and an arp request is sent instead.  When an arp
                   reply is received, the last held packet is send.  Other-
                   wise, the looked up address is returned and written into
                   the storage desten points to.  arpresolve() returns 1, if a
                   valid address was stored to desten, and the packet can be
                   sent immediately.  Else a 0 is returned.

     arpintr()     When an arp packet is received, the network driver (class)
                   input interrupt handler queues the packet on the arpintrq
                   queue, and requests an arpintr() soft interrupt callback.
                   arpintr() dequeues the packets, performs sanity checks and
                   calls (for IPv4 arp packets, which are the only ones sup-
                   ported currently) the in_arpinput() function.
                   in_arpinput() either generates a reply to request packets,
                   and adds the sender address translation to the routing ta-
                   ble, if a matching route entry is found.  If the route
                   entry contained a pointer to a held packet, that packet is
                   sent.

SEE ALSO
     ether_ifattach(9)
     Plummer, D., "RFC826", An Ethernet Address Resolution Protocol.

AUTHORS
     UCB CSRG (original implementation)
     Ignatios Souvatzis (support for non-Ethernet)

CODE REFERENCES
     The ARP code is implemented in sys/net/if_arp.h, sys/netinet/if_inarp.h
     and sys/netinet/if_arp.c.

STANDARDS
     RFC 826

HISTORY
     Rewritten to support other than Ethernet link level addresses in
     NetBSD 1.3.

NetBSD 5.0_STABLE                March 3, 1997               NetBSD 5.0_STABLE
