sub ping
{
  my ($self,
      $host,              # Name or IP number of host to ping
      $timeout,           # Seconds after which ping times out
      ) = @_;
  my ($ip,                # Packed IP number of $host
      $ret,               # The return value
      $ping_time,         # When ping began
      );

  croak("Usage: \$p->ping(\$host [, \$timeout])") unless @_ == 2 || @_ == 3;
  $timeout = $self->{"timeout"} unless $timeout;
  croak("Timeout must be greater than 0 seconds") if $timeout <= 0;

  $ip = inet_aton($host);
  return () unless defined($ip);      # Does host exist?

  # Dispatch to the appropriate routine.
  $ping_time = &time();
  if ($self->{"proto"} eq "external") {
    $ret = $self->ping_external($ip, $timeout);
  }
  elsif ($self->{"proto"} eq "udp") {
    $ret = $self->ping_udp($ip, $timeout);
  }
  elsif ($self->{"proto"} eq "icmp") {
    $ret = $self->ping_icmp($ip, $timeout);
  }
  elsif ($self->{"proto"} eq "tcp") {
    $ret = $self->ping_tcp($ip, $timeout);
  }
  elsif ($self->{"proto"} eq "stream") {
    $ret = $self->ping_stream($ip, $timeout);
  }
  elsif ($self->{"proto"} eq "syn") {
    $ret = $self->ping_syn($host, $ip, $ping_time, $ping_time+$timeout);
  } else {
    croak("Unknown protocol \"$self->{proto}\" in ping()");
  }

  return wantarray ? ($ret, &time() - $ping_time, $self->ntop($ip)) : $ret;
}