in_pktinfo(2type)                                            in_pktinfo(2type)

NAME
       in_pktinfo - information about the incoming packet

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <netinet/in.h>

       struct in_pktinfo {
           unsigned int    ipi_ifindex;   /* Interface index */
           struct in_addr  ipi_spec_dst;  /* Local address */
           struct in_addr  ipi_addr;      /* Header Destination address */
       };

DESCRIPTION
   recvmsg(2)
       When returned by recvmsg(2), .ipi_ifindex is the unique index of the
       interface the packet was received on.

       .ipi_spec_dst is the preferred source address for replies to the given
       packet.

       .ipi_addr is the destination address in the packet header.

       These addresses are usually the same, but can differ for broadcast or
       multicast packets.  Depending on the configured routes, .ipi_spec_dst
       might belong to a different interface from the one that received the
       packet.

   sendmsg(2)
       If IP_PKTINFO is passed to sendmsg(2) and .ipi_spec_dst is not zero,
       then it is used as the local source address, for the routing table
       lookup, and for setting up IP source route options.

       When .ipi_ifindex is not zero, the primary local address of the
       interface specified by the index overwrites .ipi_spec_dst for the
       routing table lookup.

       .ipi_addr is ignored.

STANDARDS
       Linux.

HISTORY
       Linux 2.2.

SEE ALSO
       IP_PKTINFO(2const), setsockopt(2), ip(7)

Linux man-pages 6.17              2025-11-26                 in_pktinfo(2type)