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  20 .TH PCAP_LOOKUPNET 3PCAP "31 January 2025"
  21 .SH NAME
  22 pcap_lookupnet \- find the IPv4 network number and netmask for a device
  23 .SH SYNOPSIS
  24 .nf
  25 .ft B
  26 #include <pcap/pcap.h>
  27 .ft
  28 .LP
  29 .nf
  30 .ft B
  31 char errbuf[PCAP_ERRBUF_SIZE];
  32 .ft
  33 .LP
  34 .ft B
  35 int pcap_lookupnet(const char *device, bpf_u_int32 *netp,
  36     bpf_u_int32 *maskp, char *errbuf);
  37 .ft
  38 .fi
  39 .SH DESCRIPTION
  40 .BR pcap_lookupnet ()
  41 is used to determine the IPv4 network number and mask
  42 associated with the network device
  43 .IR device .
  44 Both
  45 .I netp
  46 and
  47 .I maskp
  48 are
  49 .B bpf_u_int32
  50 pointers, on success both values will be set in network byte order.
  51 .I errbuf
  52 is a buffer large enough to hold at least
  53 .B PCAP_ERRBUF_SIZE
  54 chars.
  55 .LP
  56 This function is not available on Windows.  It supports neither IPv6 nor
  57 multiple IPv4 addresses per interface, which obviously is not practical in
  58 modern networks.  See
  59 .BR pcap_findalldevs (3PCAP)
  60 for a more elaborate solution to the problem.
  61 .SH RETURN VALUE
  62 .BR pcap_lookupnet ()
  63 returns
  64 .B 0
  65 on success and
  66 .B PCAP_ERROR
  67 on failure. If
  68 .B PCAP_ERROR
  69 is returned,
  70 .I errbuf
  71 is filled in with an appropriate error message.
  72 .SH SEE ALSO
  73 .BR pcap (3PCAP)