anchor.diff:        example = "131.211.84.1";
         description = ''
           The default gateway.  It can be left empty if it is auto-detected through DHCP.
  +      '';
  +    };
  +
  +    networking.defaultGatewayWindowSize = mkOption {
  +      default = "";
  +      example = "524288";
  +      description = ''
  +        The window size of the default gateway. It limits maximal data bursts that TCP peers
  +        are allowed to send to us.
         '';
       };
   
  
positive.code:                 # Set the default gateway.
                  ${optionalString (cfg.defaultGateway != "") ''
                    # FIXME: get rid of "|| true" (necessary to make it idempotent).
                    ip route add default via "${cfg.defaultGateway}" || true
                  ''}
  
                  # Turn on forwarding if any interface has enabled proxy_arp.
  
negative.code: let
  
    cfg = config.networking;
  
    windowSize = if cfg.defaultGatewayWindowSize != "" then 
      "window ${cfg.defaultGatewayWindowSize}" else "";
  
    interfaces = attrValues cfg.interfaces;
    hasVirtuals = any (i: i.virtual) interfaces;
  
  