code: def _get_default_iface_linux():
      # type: () -> Optional[str]
      
      data = _read_file('/proc/net/route')
      if data is not None and len(data) > 1:
          for line in data.split('\n')[1:-1]:
              iface_name, dest = line.split('\t')[:2]
              if dest == '00000000':
                  return iface_name
      return None
docs: Get the default interface by reading /proc/net/route.
  
      This is the same source as the `route` command, however it's much
      faster to read this file than to call `route`. If it fails for whatever
      reason, we can fall back on the system commands (e.g for a platform
      that has a route command, but maybe doesn't use /proc?).