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ARP(9)                     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, const struct rtentry *rt, struct mbuf *m,
         const struct sockaddr *dst, void *desten, size_t destlen);

     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
                   duplicate 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
                   created.  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.
                   Otherwise, 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
                   supported currently) the in_arpinput() function.
                   in_arpinput() either generates a reply to request packets,
                   and adds the sender address translation to the routing
                   table, if a matching route entry is found.  If the route
                   entry contained a pointer to a held packet, that packet is
                   sent.

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

SEE ALSO
     ether_ifattach(9)

     Plummer, D., "RFC826", An Ethernet Address Resolution Protocol.

STANDARDS
     RFC 826

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

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

NetBSD 10.99                   September 1, 2019                  NetBSD 10.99