sub decode_header
{
   my $buff = shift;
   my %lsa;
   print dump_hex(substr($buff,0,20));
   ($lsa{age},
    $lsa{options},
    $lsa{type},
    $lsa{lsid},
    $lsa{advRouter},
    $lsa{seqNo},
    $lsa{checksum},
    $lsa{length}) = unpack('nCCNNNnn',$buff);
    $lsa{lsid} = N_to_dottedQuad($lsa{lsid});
    $lsa{advRouter} = N_to_dottedQuad($lsa{advRouter});
    $lsa{type} = $OSPF{LSTYPE}{$lsa{type}};
    $lsa{options} = decode_lsa_options($lsa{options});
    return \%lsa;
}