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Installation Documentation

IPNetShareX Options

 

  • Subnet Mask.
    A subnet mask specifies a range of IP addresses (when combined with an IP Address). The subnet mask is used to differentiate between internal and external network traffic, that is, which IP addresses are in the valid network number range for your network. Type this into the subnet field in all computers sharing this connection. It may be different than your External Interface's subnet mask (found in System Preferences->Network). Defaults to 255.255.255.0.

    For more help understanding subnet masks, refer to the Subnet Calculator in IPNetMonitorX (available from www.sustworks.com). A subnet mask can also be represented by a prifix length (CIDR notation) indicating the
    number of bits used for the network number part of an IP address.

  • Router Address
    The IP address of your internal Interface is the IP number you will enter for the router address on all other computers on the network. Once again, it should be different from your External Interface's router address. Defaults to 192.168.0.1 (Safe addresses to use are in the 192.168.x.x and 10.0.x.x range)

  • Preserve Ports
    IPNetShareX will try to keep the same port number when altering outgoing packets. With this option, protocols such as RPC will have a better chance of working. If it is not possible to maintain the port number, it will be silently changed as per normal.

  • Use Sockets
    Allocates sockets in order to establish FTP data and IRC DCC send connections. This option uses more system resources, but guarantees successful connections when port numbers conflict.

  • Create Aliasing Log
    Logs various aliasing statistics and information to the file /var/log/alias.log. This file is truncated each time internet sharing is started.

  • Deny incoming requests
    Rejects packets destined for the current IP number that have no entry in the internal translation table.

  • Create Denial Log
    Logs denied incoming packets via syslog.

  • External Interface
    The interface you receive data from your ISP through (usually either a modem or a ethernet card connected to a DSL modem, Cable modem, or ethernet hub).

  • Internal Interface
    The interface that your internal network is connected to. This can be the same as your external interface.

  • Dynamic IP Binding
    IPNetShareX will monitor the External Interface for changes. If the interface's IP number is changed, IPNetShareX, will dynamically alter routing table. This option should be used if you are connecting with a dynamically assigned IP address from PPP, DHCP or PPPoE. It cannot be used for Single Ethernet configurations.

  • Local Caching Name Server
    This option will start a local daemon to store domain name information. This is useful if your name server is assigned dynamically as is the case with some implementations of PPPoE.

  • Load at Startup
    This creates the files necessary to start natd and domain name services on startup. You can see the actual unix commands IPNetShareX generates by looking in /library/startupitems after enabling Load on Startup. Notice IPNetShareX itself does not run when your system is restarted.

Typical Setups

Here are some suggestions for how to configure the most common setups
(find the version that best fits your network's configuration).:

Tips:

  • When configuring a secondary interface in the network control panel, make sure the router address is set to 0.0.0.0, not the same as its IP address and the router address in IPNetShareX.
  • If you are using PPPoE and your Domain Name Server (DNS) information is dynamically assigned, enable the "Local Caching Name Server" option.
  • If you have only one Ethernet card you generally do not have to change anything for the External Interface in the network control panel of the computer that will serve as your gateway.
  • If you are sharing between two computers which each have an Airport card but you have no hardware base station, create a "computer-to-computer" network and then configure IPNetShareX to use the Airport card as its internal interface on the server.
  • To start NAT services when you start up your machine, enable the "Load on Startup" option.


Dial-up modem connection (using PPP), built-in ethernet card to internal network.

Subnet Mask: 255.255.255.0
Router Address: 192.168.0.1
Preserve Ports: Yes
Use Sockets: Yes
Create Aliasing Log: Yes
Deny Incoming Requests: Yes
Create Denial Log: No
External Interface: Modem or PPPoE (ppp0)
Internal Interface: Built-in Ethernet (en0)
Dynamic IP Binding: Yes

Dial-up modem connection (using PPP), Airport network.

Subnet Mask: 255.255.255.0
Router Address: 10.0.1.1
Preserve Ports: Yes
Use Sockets: Yes
Create Aliasing Log: Yes
Deny Incoming Requests: Yes
Create Denial Log: No
External Interface: Modem or PPPoE (ppp0)
Internal Interface: AirPort (en2)
Dynamic IP Binding: Yes

DSL/Cable or other ethernet based connection (static IP), Airport network.

Subnet Mask: 255.255.255.0
Router Address: 10.0.1.1
Preserve Ports: Yes
Use Sockets: Yes
Create Aliasing Log: Yes
Deny Incoming Requests: No
Create Denial Log: No
External Interface: Built-in Ethernet (en0)
Internal Interface: AirPort (en2)
Dynamic IP Binding: No

DSL/Cable or other ethernet based connection (DHCP or other dynamically assigned IP), Airport network.

Subnet Mask: 255.255.255.0
Router Address: 10.0.1.1
Preserve Ports: Yes
Use Sockets: Yes
Create Aliasing Log: Yes
Deny Incoming Requests: No
Create Denial Log: No
External Interface: Built-in Ethernet (en0)
Internal Interface: AirPort (en2)
Dynamic IP Binding: Yes

DSL/Cable or other ethernet based connection (static IP), secondary ethernet card to internal network.

Subnet Mask: 255.255.255.0
Router Address: 192.168.0.1
Preserve Ports: Yes
Use Sockets: Yes
Create Aliasing Log: Yes
Deny Incoming Requests: No
Create Denial Log: No
External Interface: Built-in Ethernet (en0)
Internal Interface: PCI Ethernet Slot C, Port 3 (en1)
Dynamic IP Binding: No

DSL/Cable or other ethernet based connection (DHCP or other dynamically assigned IP), secondary ethernet card to internal network.

Subnet Mask: 255.255.255.0
Router Address: 192.168.0.1
Preserve Ports: Yes
Use Sockets: Yes
Create Aliasing Log: Yes
Deny Incoming Requests: No
Create Denial Log: No
External Interface: Built-in Ethernet (en0)
Internal Interface: PCI Ethernet Slot C, Port 3 (en1)
Dynamic IP Binding: Yes

DSL/Cable or other ethernet based connection (static IP), one ethernet interface.

Subnet Mask: 255.255.255.0
Router Address: 192.168.0.1
Preserve Ports: Yes
Use Sockets: Yes
Create Aliasing Log: Yes
Deny Incoming Requests: No
Create Denial Log: No
External Interface: Built-in Ethernet (en0)
Internal Interface: Built-in Ethernet (en0)
Dynamic IP Binding: No

DSL or other ethernet based connection (dynamically assigned IP), one ethernet interface.

You will need to duplicate the ethernet connection in the network control panel as follows:

Click the "Show:" popup menu and choose "Active Network Ports"
Click "New..."
Put "Built-in Ethernet Local" as the name
Select "Built-in Ethernet" as the port
Click "OK"

Now, you will have two different copies of the ethernet interface in the "Show:" popup menu. Set up "Built-in Ethernet" as the external (DHCP) interface, and "Built-in Ethernet Local" as the internal interface.

Remote Computer Setup

To set up a computer to use the IPNetShareX server:

  1. Enter a unique IP address in a chosen class other than the router address.

    Example: (router address = 192.168.0.1)
    IP for client machine 1: 192.168.0.2
    IP for client machine 3: 192.168.0.3
    ...
    IP for client machine 50: 192.168.0.50

  2. Enter the subnet mask into the corresponding field (sometimes called netmask or subnet in other operating systems).

  3. Enter the router address into the correct field (sometimes called default router).

  4. If you enabled the "Local Caching Name Server" option, Enter the IP address of the machine with IPNetShareX installed on it (in this case 192.168.0.1) as the domain name server (sometime called name server or DNS). Otherwise, specify a valid Name Server address directly (should be the same as the name server address used by your IPNetShareX server). If your IPNetShareX server is configured via DHCP and you don't know the name server address it received, you can use the DHCP Lease tool in IPNetMonitorX to find it (available from www.sustworks.com), or contact your ISP to request the name server address.

  5. Save or Apply your settings.

What If It Doesn't Work?

IPNetShareX is a relatively simple utility for configuring unix "natd" and "ipfw". Everything it does you can also do from a terminal window using unix command lines directly. This section describes the most common problems you might encounter.

To configure any computer to use TCP/IP, you must specify four pieces of information: IP address, network mask, router address, and name server address. You must specify these correctly for each network interface on each computer. If you are not sure what values to use, you may need help with TCP/IP.

The most common problem is not specifying a valid Name Server address at each client computer.

With regard to IPNetShareX itself, the most common problems are:

(1) Trying to configure unix "natd" or "ipfw" more than once.

Check the directory /library/startupitems on your Mac OS X system disk to make sure there are no other startup items that are trying to configure "natd" or "ipfw". Such items are typically named "NAT", "gNAT" or for some other firewall tool. IPNetShareX is not compatible with Norton Personal Firewall, Fire Walker, or Brick House at this time.

Next, you can verify how IPNetShareX has configured your system from a terminal window. 


    - type "ifconfig -a" to see a list of configured interfaces.
      You might copy and paste this into any message asking for help.
      You should have at least two configured interfaces on your
      gateway machine corresponding to your External and Internal
      IP interfaces for Internet sharing.
                  
    - type "sudo ipfw list" to see a list of firewall rules.
      This should read similar to the listing below but the
      name of the interface "en0" will depend on your configuration:
                  
      00095 divert 8668 ip from any to any via en0
      65530 allow ip from any to any
      65535 allow ip from any to any

The first rule (#95) is critical and must be first.

(2) Not aware of natd's limitations and how to test it.


    - If you use a single Ethernet configuration (both internal
      and external interface on the same physical Ethernet),
      you may have trouble using DHCP to configure your external interface.
      This limitation is due to Mac OS X's DHCP client not
      distinguishing multiple IP interfaces on the same Ethernet.
      Try creating a duplicate Ethernet connection in the Network
      Preferences panel that is not configured via DHCP.
                  
    - You may not be able to use ping or traceroute through natd.
      Use domain name lookups instead.
                  
    - If you are using a PPP dialup connection, you may need
      to restart Internet Sharing each time your IP address changes.
      (IPNetShareX uses ppp_up and ppp_down scripts to work around this
       but some users still report difficulties).
                  
    - You should not manually change your external IP address while
      "natd" is running or you will likely render your Internet
      connection inoperative.  If this happens, stop Internet Sharing,
      remove any "natd" startup items, and restart your system.

(3) Custom installed Mac OS X and neglected to install the BSD subsystem

IPNetShareX requires the BSD subsystem to run "natd".

(4) Mixing old and new versions of the software (gNAT and IPNetShareX)

If you have previously configured Internet Sharing to "Load on startup", unselect this using your previous version of the software before installing the latest version from our website.

(5) MTU conflicts when using PPPoE.

Normally Ethernet has an MTU (Maximum Transfer Unit) of 1500 bytes. PPPoE reduces this to 1492. Unfortunately most PPPoE servers are broken and do not handle oversize datagrams correctly. The work around is to reduce the MTU to 1492 or lower at each of your client machines. You can use our IPNetTuner(X) available from our website for this purpose. Under Mac OS X, you can also use a unix terminal command similar to the following: 


                        sudo ifconfig en1 mtu 1492

IPNetRouter provides automatic MSS clamping to work around this problem for you.

Need More Help?

IPNetShareX is free for personal, educational, or non-profit use but does not include one-on-one technical support. You are welcome to join our NetTalk discussion list and post your support questions there. You may receive Priority Support for IPNetShareX by purchasing a Continued Care subscription on our web site or upgrading to IPNetShareX Pro.

IPNetShareX Pro users are encouraged to use our support center at http://www.sustworks.com/site/sup.html

© Copyright 2001-02, Sustainable Softworks Inc. with thanks to Ben Lachman

Please send any comments, suggestions or bug reports to:

http://www.sustworks.com/site/sup.html

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