#!/usr/bin/awk
##############################################################################
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License version 2 as
# published by the Free Software Foundation.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# Copyright (C) 2016 Eric Luehrsen
#
##############################################################################
#
# Turn DHCP records into meaningful A, AAAA, and PTR records. Also lift a
# function from dnsmasq and use DHCPv4 MAC to find IPV6 SLAAC hosts.
#
# External Parameters
#   "hostfile" = where this script will cache host DNS data
#   "domain" = text domain suffix
#   "bslaac" = boolean, use DHCPv4 MAC to find GA and ULA IPV6 SLAAC
#   "bisolt" = boolean, format <host>.<network>.<domain>. so you can isolate
#   "bconf"  = boolean, write conf file format rather than pipe records
#
##############################################################################

/^#/ {
  # We need to pick out DHCP v4 or v6 records
  net = $2 ; id = $3 ; cls = $4 ; hst = $5 ; adr = $9 ; adr2 = $10
  cdr = adr ;
  cdr2 = adr2 ;
  sub( /\/.*/, "", adr ) ;
  sub( /.*\//, "", cdr ) ;
  sub( /\/.*/, "", adr2 ) ;
  sub( /.*\//, "", cdr2 ) ;


  if ( bisolt == 1 ) {
    # TODO: this might be better with a substituion option,
    # or per DHCP pool do-not-DNS option, but its getting busy here.
    fqdn = net
    fqdn = sub( /\./, "-", fqdn ) ;
    fqdn = tolower( hst "." fqdn "." domain ) ;
  }

  else {
    fqdn = tolower( hst "." domain ) ;
  }


  if ( cls == "ipv4" ) {
    if ( NF == 8 ) {
      # odhcpd errata in field format without host name
      adr = $8 ; hst = "-" ; cdr = adr ;
      sub( /\/.*/, "", adr ) ;
      sub( /.*\//, "", cdr ) ;
    }


    if (( cdr == 32 ) && ( hst != "-" )) {
      # only for provided hostnames and full /32 assignments
      ptr = adr ; qpr = "" ; split( ptr, ptr, "." ) ;
      slaac = slaac_eui64( id ) ;


      if ( bconf == 1 ) {
        x = ( "local-data: \"" fqdn ". 300 IN A " adr "\"" ) ;
        y = ( "local-data-ptr: \"" adr " 300 " fqdn "\"" ) ;
        print ( x "\n" y "\n" ) > hostfile ;
      }

      else {
        for( i=1; i<=4; i++ ) { qpr = ( ptr[i] "." qpr) ; }
        x = ( fqdn ". 300 IN A " adr ) ;
        y = ( qpr "in-addr.arpa. 300 IN PTR " fqdn ) ;
        print ( x "\n" y ) > hostfile ;
      }


      if (( bslaac == 1 ) && ( slaac != 0 )) {
        # UCI option to discover IPV6 routed SLAAC addresses
        # NOT TODO - ping probe take too long when added in awk-rule loop
        cmd = ( "ip -6 --oneline route show dev " net ) ;


        while ( ( cmd | getline adr ) > 0 ) {
          if (( substr( adr, 1, 5 ) <= "fdff:" ) \
          && ( index( adr, "anycast" ) == 0 ) \
          && ( index( adr, "via" ) == 0 )) {
            # GA or ULA routed addresses only (not LL or MC)
            sub( /\/.*/, "", adr ) ;
            adr = ( adr slaac ) ;


            if ( split( adr, tmp0, ":" ) > 8 ) {
              sub( "::", ":", adr ) ;
            }


            if ( bconf == 1 ) {
              x = ( "local-data: \"" fqdn ". 300 IN AAAA " adr "\"" ) ;
              y = ( "local-data-ptr: \"" adr " 300 " fqdn "\"" ) ;
              print ( x "\n" y "\n" ) > hostfile ;
            }

            else {
              qpr = ipv6_ptr( adr ) ;
              x = ( fqdn ". 300 IN AAAA " adr ) ;
              y = ( qpr ". 300 IN PTR " fqdn ) ;
              print ( x "\n" y ) > hostfile ;
            }
          }
        }


        close( cmd ) ;
      }
    }
  }

  else {
    if (( cdr == 128 ) && ( hst != "-" )) {
      if ( bconf == 1 ) {
        x = ( "local-data: \"" fqdn ". 300 IN AAAA " adr "\"" ) ;
        y = ( "local-data-ptr: \"" adr " 300 " fqdn "\"" ) ;
        print ( x "\n" y "\n" ) > hostfile ;
      }

      else {
        # only for provided hostnames and full /128 assignments
        qpr = ipv6_ptr( adr ) ;
        x = ( fqdn ". 300 IN AAAA " adr ) ;
        y = ( qpr ". 300 IN PTR " fqdn ) ;
        print ( x "\n" y ) > hostfile ;
      }
    }

    if (( cdr2 == 128 ) && ( hst != "-" )) {
      if ( bconf == 1 ) {
        x = ( "local-data: \"" fqdn ". 300 IN AAAA " adr2 "\"" ) ;
        y = ( "local-data-ptr: \"" adr2 " 300 " fqdn "\"" ) ;
        print ( x "\n" y "\n" ) > hostfile ;
      }

      else {
        # odhcp puts GA and ULA on the same line (position 9 and 10)
        qpr2 = ipv6_ptr( adr2 ) ;
        x = ( fqdn ". 300 IN AAAA " adr2 ) ;
        y = ( qpr2 ". 300 IN PTR " fqdn ) ;
        print ( x "\n" y ) > hostfile ;
      }
    }
  }
}

##############################################################################

function ipv6_ptr( ipv6,    arpa, ary, end, i, j, new6, sz, start ) {
  # IPV6 colon flexibility is a challenge when creating [ptr].ip6.arpa.
  sz = split( ipv6, ary, ":" ) ; end = 9 - sz ;


  for( i=1; i<=sz; i++ ) {
    if( length(ary[i]) == 0 ) {
      for( j=1; j<=end; j++ ) { ary[i] = ( ary[i] "0000" ) ; }
    }

    else {
      ary[i] = substr( ( "0000" ary[i] ), length( ary[i] )+5-4 ) ;
    }
  }


  new6 = ary[1] ;
  for( i = 2; i <= sz; i++ ) { new6 = ( new6 ary[i] ) ; }
  start = length( new6 ) ;
  for( i=start; i>0; i-- ) { arpa = ( arpa substr( new6, i, 1 ) ) ; } ;
  gsub( /./, "&\.", arpa ) ; arpa = ( arpa "ip6.arpa" ) ;

  return arpa ;
}

##############################################################################

function slaac_eui64( mac,    ary, glbit, eui64 ) {
  if ( length(mac) >= 12 ) {
    # RFC2373 and use DHCPv4 registered MAC to find SLAAC addresses
    split( mac , ary , "" ) ;
    glbit = ( "0x" ary[2] ) ;
    glbit = sprintf( "%d", glbit ) ;
    glbit = or( glbit, 2 ) ;
    ary[2] = sprintf( "%x", glbit ) ;
    eui64 = ( ary[1] ary[2] ary[3] ary[4] ":" ary[5] ary[6] "ff:fe" ) ;
    eui64 = ( eui64 ary[7] ary[8] ":" ary[9] ary[10]  ary[11] ary[12] ) ;
  }

  else {
    eui64 = 0 ;
  }


  return eui64 ;
}

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