anchor.diff:  let
   
     cfg = config.networking;
  -
  -  windowSize = if cfg.defaultGatewayWindowSize != "" then 
  -    "window ${cfg.defaultGatewayWindowSize}" else "";
  -
     interfaces = attrValues cfg.interfaces;
     hasVirtuals = any (i: i.virtual) interfaces;
   
  
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}" ${windowSize} || true
                  ''}
  
                  # Turn on forwarding if any interface has enabled proxy_arp.
  
negative.code:     };
  
      networking.defaultGatewayWindowSize = mkOption {
        default = null;
        example = 524288;
        type = types.nullOr types.int;
        description = ''
          The window size of the default gateway. It limits maximal data bursts that TCP peers
          are allowed to send to us.
  