  Linux IP Masquerade mini HOWTO
  Ambrose Au, achau@wwonline.com
  v1.00, 1 January 1997

  This document describes how to enable IP masquerade feature on a Linux
  host, allowing connected computers that do not have registered Inter
  net IP addresses to connect to the Internet through your Linux box.

  1.  Introduction

  1.1.  Introduction

  This document describes how to enable IP masquerade feature on a Linux
  host, allowing connected computers that do not have registered
  Internet IP addresses to connect to the Internet through your Linux
  box.  It is possible to connect your machines to the Linux host with
  ethernet, as well as other kinds of connection such as a dialup ppp
  link. This document will emphasize on ethernet connection, since it
  should be the most likely case.

       This document is intended for users using kernels 2.0.x.
       Development kernels 2.1.x are NOT covered.

  1.2.  Foreword, Feedback & Credits

  First of all, I would like to let you know that I am NOT a
  knowledgeable nor an experienced user of IP masquerade.

  I find it very confusing as a new user setting up IP masquerade on a
  newer kernel, i.e. 2.x kernel.  Although there is a FAQ and a mailing
  list, there is no document dedicates on that; and there are some
  requests on the mailing list for such a HOWTO. So, I decided to write
  this up as a starting point for new users, and possibly a building
  block for knowledgeable users to build on for documentation. If you
  think I'm not doing a good job, feel free to tell me so that I can
  make it better.

  This document is heavily based on the original FAQ by Ken Eves , and
  numerous helpful messages in the ip_masq mailing list. And a special
  thanks to Mr. Matthew Driver whose mailing list message inspired me to
  set up ip_masq and eventually writing this.

  Please feel free to send any feedback or comments to
  achau@wwonline.com if I'm mistaken on any information, or if any
  information is missing. Your invaluable feedback will certainly be
  influencing the future of this HOWTO!

  This HOWTO is meant to be a quick guide to get your IP Masquerade
  working in the shortest time.  The latest news and information can be
  found at the IP Masquerade Resource web page that I maintained.  If
  you have any technical questions on IP Masquerade, please join the IP
  Masquerade Mailing List instead of sending email to me since I have
  limited time, and the developers of IP_Masq are more capable of
  answering your questions.

  The latest version of this document can be found at the IP Masquerade
  Resource, which also contains the HTML and postscript version:

    http://www.wwonline.com/~achau/ipmasq/

    http://www.hwy401.com/achau/ipmasq/

    http://www.leg.uct.ac.za/mirrors/ipmasq/

    http://130.89.230.132/linux/ipmasq/

  1.3.  Copyright & Disclaimer

  This document is copyright(c) 1996 Ambrose Au, and it's a free
  document. You can redistribute it under the terms of the GNU General
  Public License.

  The information and other contents in this document are to the best of
  my knowledge. However, ip_masq is experimental, and there is chance
  that I make mistakes as well; so you should determine if you want to
  follow the information in this document.

  Nobody is responsible for any damage on your computers and any other
  losses by using the information on this document. i.e.

       THE AUTHOR IS NOT RESPONSIBLE FOR ANY DAMAGES INCURRED DUE
       TO ACTIONS TAKEN BASED ON THE INFORMATION IN THIS DOCUMENT.

  2.  Background Knowledge

  2.1.  What is IP Masquerade?

  IP Masquerade is a developing networking function in Linux. If a Linux
  host is connected to the Internet with IP Masquerade enabled, then
  computers connecting to it (either on the same LAN or connected with
  modems) can reach the Internet as well, even though they have no
  official assigned IP addresses.

  This allows a set of machines to invisibly access the Internet hidden
  behind a gateway system, which appears to be the only system using the
  Internet.  Breaking the security of a well set-up masquerading system
  should be considerably more difficult than breaking a good packet
  filter based firewall (assuming there are no bugs in either).

  2.2.  Current Status

  IP Masquerade is still at its experimental stages. However, kernels
  since 1.3.x had built-in support already. Many individuals and even
  companies are using it, with satisfactory results.

  Browsing web pages and telnet are reported to work well over ip_masq.
  FTP, IRC and listening to Real Audio are working with certain modules
  loaded. Other network streaming audio such as True Speech and Internet
  Wave work too. Some fellow users on the mailing list even tried video
  conferencing software.   Ping is now working, with the newly available
  ICMP patch

  Please refer to section 4.3 for a more complete listing of software
  supported.

  IP Masquerade works well with 'client machines' on several different
  OS and platforms. There are successful cases with systems using Unix,
  Windows 95, Windows NT, Windows for Workgroup(with TCP/IP package),
  OS/2, Macintosh System's OS with Mac TCP, Mac Open Transport, DOS with
  NCSA Telnet package, VAX, Alpha with Linux, and even Amiga with AmiTCP
  or AS225-stack.

  2.3.  Who Can Benefit From IP Masquerade?

    If you have a Linux host connected to the Internet, and

    if you have some computers running TCP/IP connected to that Linux
     box on a local subnet, and/or

    if your Linux host has more than one modem and acts as a PPP or
     SLIP server connecting to others, which

    those OTHER machines do not have official assigned IP addresses.
     (these machines are represented by OTHER machines hereby)

    And of course, if you want those OTHER machines to make it onto the
     Internet without spending extra bucks :)

  2.4.  Who Doesn't Need IP Masquerade?

    If your machine is a stand-alone Linux host connected to the
     Internet, then it is pointless to have ip_masq running, or

    if you already have assigned addresses for your OTHER machines,
     then you don't need IP Masquerade,

    and of course, if you don't like the idea of a 'free ride'.

  2.5.  How IP Masquerade Works?

  From IP Masquerade FAQ by Ken Eves:

    Here is a drawing of the most simple setup:

       SLIP/PPP         +------------+                         +-------------+
       to provider      |  Linux     |       SLIP/PPP          | Anybox      |
      <---------- modem1|            |modem2 ----------- modem |             |
        111.222.333.444 |            |           192.168.1.100 |             |
                        +------------+                         +-------------+

      In the above drawing a Linux box with ip_masquerading installed and
    running is connected to the Internet via SLIP/or/PPP using modem1.  It has
    an assigned IP address of 111.222.333.444.  It is setup that modem2 allows
    callers to login and start a SLIP/or/PPP connection.

      The second system (which doesn't have to be running Linux) calls into the
    Linux box and starts a SLIP/or/PPP connection.  It does NOT have an assigned
    IP address on the Internet so it uses 192.168.1.100. (see below)

      With ip_masquerade and the routing configured properly the machine
    Anybox can interact with the Internet as if it was really connected (with a
    few exceptions).

  Quoting Pauline Middelink:
    Do not forget to mention the ANYBOX should have the Linux box
    as its gateway (whether is be the default route or just a subnet
    is no matter). If the ANYBOX can not do this, the Linux machine
    should do a proxy arp for all routed address, but the setup of
    proxy arp is beyond the scope of the document.

  The following is an excerpt from a post on comp.os.linux.networking which
  has been edited to match the names used in the above example:
     o I tell machine ANYBOX that my slipped linux box is its gateway.
     o When a packet comes into the linux box from ANYBOX, it will assign it
       new source port number, and slap its own ip address in the packet
       header, saving the originals.  It will then send the modified packet
       out over the SLIP/or/PPP interface to the Internet.
     o When a packet comes from the Internet to the linux box, if the port
       number is one of those assigned above, it will get the original
       port and ip address, put them back in the packet header, and send the
       packet to ANYBOX.
     o The host that sent the packet will never know the difference.

  An IP Masquerading Example

  typical example is given in the diagram below:-

      +----------+
      |          |  Ethernet
      | abox     |::::::
      |          |2    :192.168.1.x
      +----------+     :
                       :   +----------+   PPP
      +----------+     :  1|  Linux   |   link
      |          |     ::::| masq-gate|:::::::::// Internet
      | bbox     |::::::   |          |
      |          |3    :   +----------+
      +----------+     :
                       :
      +----------+     :
      |          |     :
      | cbox     |::::::
      |          |4
      +----------+

      <-Internal Network->

  In this example there are 4 computer systems that we are concerned
  about (there is presumably also something on the far right that your
  IP connection to the internet comes through, and there is something
  (far off the page) on the internet that you are interested in exchang
  ing information with).  The Linux system masq-gate is the masquerading
  gateway for the internal network of machines abox, bbox and cbox to
  get to the internet.  The internal network uses one of the assigned
  private network addresses, in this case the class C network
  192.168.1.0, with the linux box having address 192.168.1.1 and the
  other systems having addresses on that network.

  The three machines abox, bbox and cbox (which can, by the way, be
  running any operating system as long as they can speak IP - such as
  Windows 95, Macintosh MacTCP or even another linux box) can connect to
  other machines on the internet, however the masquerading system masq-
  gate converts all of their connections so that they appear to
  originate from masq-gate, and arranges that data coming back in to a
  masqueraded connection is relayed back to the originating system - so
  the systems on the internal network see a direct route to the internet
  and are unaware that their data is being masqueraded.

  2.6.  Requirements for Using IP Masquerade on Linux 2.x

    Kernel 2.0.x source available from
     ftp://ftp.funet.fi/pub/Linux/kernel/src/v2.0/
     (Yes, you'll have to compile your kernel with certain supports....
     The latest stable kernel is recommended)

    Loadable kernel modules, preferably 2.0.0 or newer available from
     http://www.pi.se/blox/modules/modules-2.0.0.tar.gz
     (modules-1.3.57 is the minimal requirement)

    A well set up TCP/IP network
     covered in Linux NET-2 HOWTO
     <http://www.caldera.com/LDP/HOWTO/NET-2-HOWTO.html> and the Network
     Administrator's Guide <http://linuxwww.db.erau.edu/NAG/>

    Connectivity to Internet for your Linux host
     covered in Linux ISP Hookup HOWTO
     <http://www.caldera.com/LDP/HOWTO/ISP-Hookup-HOWTO.html>, Linux PPP
     HOWTO <http://www.caldera.com/LDP/HOWTO/PPP-HOWTO.html> and Linux
     PPP-over-ISDN mini-HOWTO
     <http://www.caldera.com/LDP/HOWTO/mini/PPP-over-ISDN>

    Ipfwadm 2.3 or newer available from
     ftp://ftp.xos.nl/pub/linux/ipfwadm/ipfwadm-2.3.tar.gz
     more information on version requirement is on the Linux Ipfwadm
     page <http://www.xos.nl/linux/ipfwadm/>

    You can optionally apply some IP Masquerade patches to enable other
     functionality.  More information availabe on IP Masquerade
     Resources <http://www.wwonline.com/~achau/ipmasq/> (these patches
     apply to all 2.0.x kernels)

  3.  Setting Up IP Masquerade

       If your private network contains any vital information,
       think twice before using IP Masquerade.  This may be a GATE
       WAY for you to get to the Internet, and vice versa for some
       one on the other side of the world to get into your network.

  3.1.  Compiling the Kernel for IP Masquerade Support

    First of all, you need the kernel source (preferably stable kernel
     version 2.0.0 or above)

    If this is your first time compiling the kernel, don't be scared.
     In fact, it's rather easy and it's covered in Linux Kernel HOWTO
     <http://www.caldera.com/LDP/HOWTO/Kernel-HOWTO.html>.

    Unpack the kernel source to /usr/src/ with a command: tar xvzf
     linux-2.0.x.tar.gz -C /usr/src, where x is the patch level beyond
     2.0
     (make sure there is a directory or symbolic link called linux )

    Apply appropriate patches.  Since new patches are coming out,
     details will not be included here.  Please refer to IP Masquerade
     Resources <http://www.wwonline.com/~achau/ipmasq/> for up-to-date
     information.

    Refer to the Kernel HOWTO and the README file in the kernel source
     directory for further instructions on compiling a kernel

    Here are the options that you need to compile in:

     Say YES to the following,

    * Prompt for development and/or incomplete code/drivers
      CONFIG_EXPERIMENTAL
      - this will allow you to select experimental ip_masq code compiled
        into the kernel

    * Enable loadable module support
      CONFIG_MODULES
      - allows you to load modules

    * Networking support
      CONFIG_NET

    * Network firewalls
      CONFIG_FIREWALL

    * TCP/IP networking
      CONFIG_INET

    * IP: forwarding/gatewaying
      CONFIG_IP_FORWARD

    * IP: firewalling
      CONFIG_IP_FIREWALL

    * IP: masquerading (EXPERIMENTAL)
      CONFIG_IP_MASQUERADE
      - although it is experimental, it is a *MUST*

    * IP: always defragment
      CONFIG_IP_ALWAYS_DEFRAG
      - highly recommended

    * Dummy net driver support
      CONFIG_DUMMY
      - recommended

  NOTE: These are just the component you need for ip_masq, select
  whatever other options you need for your specific setup.

    After compiling the kernel, you should compile and install the
     modules:

       make modules; make modules_install

    Then you should add a few lines into your /etc/rc.d/rc.local file
     (or any file you think is appropriate) to load the required modules
     reside in /lib/modules/2.0.x/ipv4/ automatically during each
     reboot:

          .
          .
          .
  /sbin/depmod -a
  /sbin/modprobe ip_masq_ftp
  /sbin/modprobe ip_masq_raudio
  /sbin/modprobe ip_masq_irc
  (and other modules such as ip_masq_cuseeme, ip_masq_vdolive
   if you have applied the patches)
          .
          .
          .

  Note: You can also load it manually before using ip_masq, but DON'T
  use kerneld for this, it will NOT work!

  3.2.  Assigning Private Network IP Address

  Since all OTHER machines do not have official assigned addressees,
  there must be a right way to allocate address to those machines.

  From IP Masquerade FAQ:

  There is an RFC (#1597) on which IP addresses are to be used on a non-
  connected network.  There are 3 blocks of numbers set aside
  specifically for this purpose. One which I use is 255 Class-C subnets
  at 192.168.1.n to 192.168.255.n .

       From RCF 1597:

       Section 3: Private Address Space

       The Internet Assigned Numbers Authority (IANA) has reserved the
       following three blocks of the IP address space for private networks:

                     10.0.0.0        -   10.255.255.255
                     172.16.0.0      -   172.31.255.255
                     192.168.0.0     -   192.168.255.255

       We will refer to the first block as "24-bit block", the second as
       "20-bit block", and to the third as "16-bit" block".  Note that the
       first block is nothing but a single class A network number, while the
       second block is a set of 16 contiguous class B network numbers, and
       third block is a set of 255 contiguous class C network numbers.

  So, if you're using a class C network, you should name your machines
  as 192.168.1.1, 1.92.168.1.2, 1.92.168.1.3, ..., 192.168.1.x

  192.168.1.1 is usually the gateway machine, which is your Linux host
  connecting to the Internet. Notice that 192.168.1.0 and 192.168.1.255
  are the Network and Broadcast address respectively, which are
  reserved. Avoid using these addresses on your machines.

  3.3.  Configuring the OTHER machines

  Besides setting the appropriate IP address for each machine, you
  should also set the appropriate gateway. In general, it is rather
  straight forward. You simply enter the address of your Linux host
  (usually 192.168.1.1) as the gateway address.

  For the Domain Name Service, you can add in any DNS available. The
  most apparent one should be the one that your Linux is using. You can
  optionally add any domain search suffix as well.

  After you have reconfigured those IP addresses, remember to restart
  the appropriate services or reboot your systems.

  The following configuration instructions assume that you are using a
  Class C network with 192.168.1.1 as your Linux host's address. Please
  note that 192.168.1.0 and 192.168.1.255 are reserved.

  3.3.1.  Configuring Windows 95

  1. If you haven't installed your network card and adapter driver, do
     so now.

  2. Go to 'Control Panel'/'Network'.

  3. Add 'TCP/IP protocol' if you don't already have it.

  4. In 'TCP/IP properties', goto 'IP Address' and set IP Address to
     192.168.1.x, (1 < x < 255), and then set Subnet Mask to
     255.255.255.0

  5. Add 192.168.1.1 as your gateway under 'Gateway'.

  6. Under 'DNS Configuration'/'DNS Server search order' add your the
     DNS that your Linux host uses (usually find in /etc/resolv.conf).
     Optionally, you can add the appropriate domain search suffix.

  7. Leave all the other settings as they are unless you know what
     you're doing.

  8. Click 'OK' on all dialog boxes and restart system.

  9. Ping the linux box to test the network connection: 'Start/Run',
     type: ping 192.168.1.1
     (This is only a LAN connection testing, you can't ping the outside
     world yet.)

  10.
     You can optionally create a HOSTS file in the windows directory so
     that you can use hostname of the machines on your LAN.  There is an
     example called HOSTS.SAM in the windows directory.

  3.3.2.  Configuring Windows for Workgroup 3.11

  1. If you haven't installed your network card and adapter driver, do
     so now.

  2. Install the TCP/IP 32b package if you don't have it already.

  3. In 'Main'/'Windows Setup'/'Network Setup', click on 'Drivers'.

  4. Highlight 'Microsoft TCP/IP-32 3.11b' in the 'Network Drivers'
     section, click 'Setup'.

  5. Set IP Address to 192.168.1.x (1 < x < 255), then set Subnet Mask
     to 255.255.255.0 and Default Gateway to 192.168.1.1

  6. Do not enable 'Automatic DHCP Configuration' and put anything in
     those 'WINS Server' input areas unless you're in a Windows NT
     domain and you know what you're doing.

  7. Click 'DNS', fill in the appropriate information mentioned in STEP
     6 of section 3.3.1, then click 'OK' when you're done with it.

  8. Click 'Advanced', check 'Enable DNS for Windows Name Resolution'
     and 'Enable LMHOSTS lookup' if you're using a look up host file,
     similar to the one mentioned in STEP 10 of section 3.3.1

  9. Click 'OK' on all dialog boxes and restart system.

  10.
     Ping the linux box to test the network connection: 'File/Run',
     type: ping 192.168.1.1
     (This is only a LAN connection testing, you can't ping the outside
     world yet.)

  3.3.3.  Configuring Windows NT 3.51

  1. If you haven't installed your network card and adapter driver, do
     so now.

  2. Go to 'Main'/'Control Panel'/'Network'

  3. Add the TCP/IP Protocol and Related Component from the 'Add
     Software' menu if you don't have TCP/IP service installed already.

  4. Under 'Network Software and Adapter Cards' section, highlight
     'TCP/IP Protocol' in the 'Installed Network Software' selection
     box.

  5. In 'TCP/IP Configuration', select the appropriate adapter, e.g.
     [1]Novell NE2000 Adapter.  Then set the IP Address to 192.168.1.x
     (1 < x < 255), then set Subnet Mask to 255.255.255.0 and Default
     Gateway to 192.168.1.1

  6. Do not enable 'Automatic DHCP Configuration' and put anything in
     those 'WINS Server' input areas unless you're in a Windows NT
     domain and you know what you're doing.

  7. Click 'DNS', fill in the appropriate information mentioned in STEP
     6 of section 3.3.1, then click 'OK' when you're done with it.

  8. Click 'Advanced', check 'Enable DNS for Windows Name Resolution'
     and 'Enable LMHOSTS lookup' if you're using a look up host file,
     similar to the one mentioned in STEP 10 of section 3.3.1

  9. Click 'OK' on all dialog boxes and restart system.

  10.
     Ping the linux box to test the network connection: 'File/Run',
     type: ping 192.168.1.1
     (This is only a LAN connection testing, you can't ping the outside
     world yet.)

  3.3.4.  Configuring UNIX Based Systems

  1. If you haven't installed your network card and recompile your
     kernel with the appropriate adapter driver, do so now.

  2. Install TCP/IP networking, such as the nettools package, if you
     don't have it already.

  3. Set IPADDR to 192.168.1.x (1 < x < 255), then set NETMASK to
     255.255.255.0, GATEWAY to 192.168.1.1, and BROADCAST to
     192.168.1.255
     For example, you can edit the /etc/sysconfig/network-scripts/ifcfg-
     eth0 file on a Red Hat Linux system, or simply do it through the
     Control Panel.
     (it's different in SunOS, BSDi, Slackware Linux, etc...)

  4. Add your domain name service (DNS) and domain search suffix in
     /etc/resolv.conf

  5. You may want to update your /etc/networks file depending on your
     settings.

  6. Restart the appropriate services, or simply restart your system.

  7. Issue a ping command: ping 192.168.1.1  to test the connection to
     your gateway machine.
     (This is only a LAN connection testing, you can't ping the outside
     world yet.)

  3.3.5.  Configuring DOS using NCSA Telnet package

  1. If you haven't installed your network card, do so now.

  2. Load the appropriate packet driver. For an NE2000 card, issue nwpd
     0x60 10 0x300, with your network card set to IRQ 10 and hardware
     address at 0x300

  3. Make a new directory, and then unpack the NCSA Telnet package:
     pkunzip tel2308b.zip

  4. Use a text editor to open the config.tel file

  5. Set myip=192.168.1.x (1 < x < 255), and netmask=255.255.255.0

  6. In this example, you should set hardware=packet, interrupt=10,
     ioaddr=60

  7. You should have at least one individual machine specification set
     as the gateway, i.e. the Linux host:

       name=default
       host=yourlinuxhostname
       hostip=192.168.1.1
       gateway=1

  8. Have another specification for a domain name service:

  name=dns.domain.com ; hostip=123.123.123.123; nameserver=1

  Note: substitute the appropriate information about the DNS that your
  Linux host uses

  9. Save your config.tel file

  10.
     Telnet to the linux box to test the network connection: telnet
     192.168.1.1

  3.3.6.  Configuring MacOS Based System Running MacTCP

  1. If you haven't installed the appropriate driver software for your
     Ethernet adapter, now would be a very good time to do so.

  2. Open the MacTCP control panel.  Select the appropriate network
     driver (Ethernet, NOT EtherTalk) and click on the 'More...' button.

  3. Under 'Obtain Address:', click 'Manually'.

  4. Under 'IP Address:', select class C from the popup menu. Ignore the
     rest of this section of the dialog box.

  5. Fill in the appropriate information under 'Domain Name Server
     Information:'.

  6. Under 'Gateway Address:', enter 192.168.1.1

  7. Click 'OK' to save the settings.  In the main window of the MacTCP
     control panel, enter the IP address of your Mac (192.168.1.x, 1 < x
     < 255) in the 'IP Address:' box.

  8. Close the MacTCP control panel.  If a dialog box pops up notifying
     you to do so, restart the system.

  9. You may optionally ping the Linux box to test the network
     connection.  If you have the freeware program MacTCP Watcher, click
     on the 'Ping' button, and enter the address of your Linux box
     (192.168.1.1) in the dialog box that pops up.  (This is only a LAN
     connection testing, you can't ping the outside world yet.)

  10.
     You can optionally create a Hosts file in your System Folder so
     that you can use the hostnames of the machines on your LAN.  The
     file should already exist in your System Folder, and should contain
     some (commented-out) sample entries which you can modify according
     to your needs.

  3.3.7.  Configuring MacOS Based System Running Open Transport

  1. If you haven't installed the appropriate driver software for your
     Ethernet adapter, now would be a very good time to do so.

  2. Open the TCP/IP Control Panel and choose 'User Mode ...' from the
     Edit menu. Make sure the user mode is set to at least 'Advanced'
     and click the 'OK' button.

  3. Choose 'Configurations...' from the File menu.  Select your
     'Default' configuration and click the 'Duplicate...' button.  Enter
     'IP Masq' (or something to let you know that this is a special
     configuration) in the 'Duplicate Configuration' dialog, it will
     probably say something like 'Deafault copy'.  Then click the 'OK'
     button, and the 'Make Active' button

  4. Select 'Ethernet' from the 'Connect via:' pop-up.

  5. Select the appropriate item from the 'Configure:' pop-up.  If you
     don't know which option to choose, you probably should re-select
     your 'Default' configuration and quit.  I use 'Manually'.

  6. Enter the IP address of your Mac (192.168.1.x, 1 < x < 255) in the
     'IP Address:' box.

  7. Enter 255.255.255.0 in the 'Subnet mask:' box.

  8. Enter 192.168.1.1 in the 'Router address:' box.

  9. Enter the IP addresses of your domain name servers in the 'Name
     server addr.:' box.

  10.
     Enter the name of your Internet domain (e.g. 'microsoft.com') in
     the 'Starting domain name' box under 'Implicit Search Path:'.

  11.
     The following procedures are optional.  Incorrect values may cause
     erratic behavior.  If your not sure, it's probably better to leave
     them blank, unchecked and/or un- selected.  Remove any information
     from those fields, if necessary.  As far as I know there is no way
     through the TCP/IP dialogs, to tell the system not to use a
     previously select alternate "Hosts" file.  If you know, I would be
     interested.
     Check the '802.3' if your network requires 802.3 frame types.

  12.
     Click the 'Options...' button to make sure that the TCP/IP is
     active.  I use the 'Load only when needed' option.  If you run and
     quit TCP/IP applications many times without rebooting your machine,
     you may find that unchecking the 'Load only when needed' option
     will prevent/reduce the effects on your machines memory management.
     With the item unchecked the TCP/IP protocol stacks are always
     loaded and available for use.  If checked, the TCP/IP stacks are
     automatically loaded when needed and un- loaded when not.  It's the
     loading and unloading process that can cause your machines memory
     to become fragmented.

  13.
     You may ping the Linux box to test the network connection.  If you
     have the freeware program MacTCP Watcher, click on the 'Ping'
     button, and enter the address of your Linux box (192.168.1.1) in
     the dialog box that pops up.  (This is only a LAN connection
     testing, you can't ping the outside world yet.)

  14.
     You can create a Hosts file in your System Folder so that you can
     use the hostnames of the machines on your LAN.  The file may or may
     not already exist in your System Folder.  If so, it should contain
     some (commented-out) sample entries which you can modify according
     to your needs.  If not, you can get a copy of the file from a
     system running MacTCP, or just create your own (it follows a subset
     of the Unix /etc/hosts file format, described on page 33 of RFC
     1035).  Once you've created the file, open the TCP/IP control
     panel, click on the 'Select Hosts File...' button, and open the
     Hosts file.

  15.
     Click the close box or choose 'Close' or 'Quit' from the File menu,
     and then click the 'Save' button to save the changes you have made.

  16.
     The changes take effect immediately, but rebooting the system won't
     hurt.

  3.3.8.  Configuring Novell network using DNS

  1. If you haven't installed the appropriate driver software for your
     Ethernet adapter, now would be a very good time to do so.

  2. Downloaded tcpip16.exe from
     <ftp.novell.com/pub/updates/unixconn/lwp5>

  3.

     edit c:\nwclient\startnet.bat

     SET NWLANGUAGE=ENGLISH
     LH LSL.COM
     LH KTC2000.COM
     LH IPXODI.COM
     LH tcpip
     LH VLM.EXE
     F:

  4.

     edit c:\nwclient\net.cfg

     Link Driver KTC2000
             Protocol IPX 0 ETHERNET_802.3
             Frame ETHERNET_802.3
             Frame Ethernet_II
             FRAME Ethernet_802.2

     NetWare DOS Requester
                FIRST NETWORK DRIVE = F
                USE DEFAULTS = OFF
                VLM = CONN.VLM
                VLM = IPXNCP.VLM
                VLM = TRAN.VLM
                VLM = SECURITY.VLM
                VLM = NDS.VLM
                VLM = BIND.VLM
                VLM = NWP.VLM
                VLM = FIO.VLM
                VLM = GENERAL.VLM
                VLM = REDIR.VLM
                VLM = PRINT.VLM
                VLM = NETX.VLM

     Link Support
             Buffers 8 1500
             MemPool 4096

     Protocol TCPIP
             PATH SCRIPT     C:\NET\SCRIPT
             PATH PROFILE    C:\NET\PROFILE
             PATH LWP_CFG    C:\NET\HSTACC
             PATH TCP_CFG    C:\NET\TCP
             ip_address      xxx.xxx.xxx.xxx
             ip_router       xxx.xxx.xxx.xxx

  5. and finally created

     c:\bin\resolv.cfg

     SEARCH DNS HOSTS SEQUENTIAL
     NAMESERVER 207.103.0.2
     NAMESERVER 207.103.11.9

  6. I hope this helps some people get their Novell Nets online, BTW
     this can be done using Netware 3.1x or 4.x

  3.3.9.  Configuring Other Systems such as OS/2

  They should be following the same theory for setup.  Check the
  sections above.  If you're interested in writing about any of these
  systems such as OS/2, or any variations of UNIX based system, please
  send a detail setup instruction to achau@wwonline.com.

  3.4.  Configuring IP Forwarding Policies

  At this point, you should have your kernel and other required packages
  installed, as well as your modules loaded. Also, the IP addresses,
  gateway, and DNS should be all set on the OTHER machines.

  Now, the only thing left to do is to use ipfwadm to forward
  appropriate packets to the appropriate machine:

       ipfwadm -F -p deny
       ipfwadm -F -a m -S yyy.yyy.yyy.yyy/x -D 0.0.0.0/0

  where x is one of the following numbers according to the class of your
  subnet, and yyy.yyy.yyy.yyy is your network address.

       netmask         | x  | Subnet
       ~~~~~~~~~~~~~~~~|~~~~|~~~~~~~~~~~~~~~
       255.0.0.0       | 8  | Class A
       255.255.0.0     | 16 | Class B
       255.255.255.0   | 24 | Class C
       255.255.255.255 | 32 | Point-to-point

  For example, if I'm on a class C subnet, I would have entered:

       ipfwadm -F -p deny
       ipfwadm -F -a m -S 192.168.1.0/24 -D 0.0.0.0/0

  The second command could have either -V 192.168.1.1 or -W eth0 added
  to it to ensure that the masqueraded packets came in through the
  appropriate interface of the system - if you are at all security
  concious (otherwise known as justifiably paranoid) then you will want
  to do this.

  Since bootp request packets comes without valid IP's once the client
  knows nothing about it, for people with a bootp server in the
  masquerade/firewall machine it is necessary to use the following
  before the deny command:

       ipfwadm -I -a accept -S 0/0 68 -D 0/0 67 -W bootp_clients_net_if_name -P udp

  You can also do it on a per machine basis.  For example, if I want
  192.168.1.2 and 192.168.1.8 to have access to the Internet, but not
  the other machines, I would have entered:

  ipfwadm -F -p deny
  ipfwadm -F -a m -S 192.168.1.2/32 -D 0.0.0.0/0
  ipfwadm -F -a m -S 192.168.1.8/32 -D 0.0.0.0/0

  Alternately, you can type the netmask instead of the value, e.g.
  192.168.1.0/255.255.255.0

  What appears to be a common mistake is to make the first command be
  this

  ipfwadm -F -p masquerade

  Do not make your default policy be masquerading - otherwise someone
  who can manipulate their routing will be able to tunnel straight back
  through your gateway, using it to masquerade their identity!

  Again, you can add these lines to the /etc/rc.local files, one of the
  rc files you prefer, or do it manually every time you need ip_masq.

  Please read section 4.4 for a detail guide on Ipfwadm

  3.5.  Testing IP Masquerade

  It's time to give it a try, after all these hard work. Make sure the
  connection of your Linux hosts to the Internet is okay.

  You can try browsing some 'INTERNET!!!' web sites on your OTHER
  machines, and see if you get it. I recommend using an IP address
  rather than a hostname on your first try, because your DNS setup may
  not be correct.

  For example, you can access Netscape's site http://home.netscape.com
  with an entry of http://198.95.249.78

  If you see that nice sailboat, then congratulations! It's working! You
  may then try one with hostname entry, and then telnet, ftp, Real
  Audio, True Speech, whatever supported by IP Masquerade.....

  So far, I have no trouble with the above settings, and it's full
  credit to the people who spend their time making this wonderful
  feature working.

  4.  Other IP Masquerade Issues and Software Support

  4.1.  Problems with IP Masquerade

  Firstly masquerading can only work with ported protocols - such as TCP
  or UDP.  It specifically will not work with ICMP, so ping and
  traceroute will not work (unless your ping and/or traceroute have been
  modified to use a different method of working).

  Some protocols will not currently work with masquerading because they
  either assume things about port numbers, or encode data in their data
  stream about addresses and ports - these latter protocols need
  specific proxies built into the masquerading code to make them work.

  4.2.  Incoming services

  Masquerading cannot handle incoming services at all.  There are a few
  ways of allowing them, but they are completely separate from
  masquerading, and are really part of standard firewall practice.

  If you do not require high levels of security then you can simply
  redirect ports.  There are various ways of doing this - I use a
  modified redir program (which I hope will be available from sunsite
  and mirrors soon). If you wish to have some level of authorisation on
  incoming connections then you can either use TCP wrappers or Xinetd on
  top of redir (0.7 or above) to allow only specific IP addresses
  through, or use some other tools.  The TIS Firewall Toolkit is a good
  place to look for tools and information.

  4.3.  Supported Client Software and Other Setup Note

  Generally, application that uses TCP and UDP should work.  If you have
  any suggestion about applications that are not compatible with IP
  Masquerade, please email to me with the name of client and a brief
  description.

  4.3.1.  Clients that Work

  General Clients

     HTTP
        all supported platforms, surfing the web

     POP & SMTP
        all supported platforms, email client

     Telnet
        all supported platforms, remote session

     FTP
        all supported platforms, with ip_masq_ftp.o module (not all
        sites work with certain clients; e.g. some sites cannot be
        reached using ws_ftp32 but works with netscape)

     Archie
        all supported platforms, file searching client (not all archie
        clients are supported)

     NNTP (USENET)
        all supported platforms, USENET news client

     VRML
        Windows(possibly all supported platforms), virtual reality
        surfing

     traceroute
        mainly UNIX based platforms, some variations may not work

     ping
        all platforms, with ICMP patch

     anything based on IRC
        all supported platforms, with ip_masq_irc.o modules

     Gopher client
        all supported platforms

     WAIS client
        all supported platforms

  Multimedia Clients

     Real Audio Player
        Windows, network streaming audio, with ip_masq_raudio module
        loaded

     True Speech Player 1.1b
        Windows, network streaming audio

     Internet Wave Player
        Windows, network streaming audio

     Worlds Chat 0.9a
        Windows, Client-Server 3D chat program

     Alpha Worlds
        Windows, Client-Server 3D chat program

     Internet Phone 3.2
        Windows, Peer-to-peer audio communications, people can reach you
        only if you initiate the call, but people cannot call you

     Powwow
        Windows, Peer-to-peer Text audio whiteboard communications,
        people can reach you only if you initiate the call, but people
        cannot call you

     CU-SeeMe
        all supported platforms, with cuseeme modules loaded, please see
        IP Masquerade Resource <http://www.wwonline.com/~achau/ipmasq/>
        for detail

     VDOLive
        Windows, with vdolive patch

  Note: Some clients such as IPhone and Powwow may work even if you're
  not the one who initiate the call by using ipautofw package (refer to
  section 4.6)

  Other Clients

     NCSA Telnet 2.3.08
        DOS, a suite containing telnet, ftp, ping, etc.

     PC-anywhere for windows 2.0
        MS-Windows, Remotely controls a PC over TCP/IP, only work if it
        is a client but not a host

     Socket Watch
        uses ntp - network time protocol

     Linux net-acct package
        Linux, network administration-account package

  4.3.2.  Clients that do not Work

     Intel Internet Phone Beta 2
        Connects but voice travels one way (out) Traffic only

     Intel Streaming Media Viewer Beta 1
        Cannot connect to server

     Netscape CoolTalk
        Cannot connect to opposite side

     talk,ntalk
        will not work - requires a kernel proxy to be written.

     WebPhone
        Cannot work at present (it makes invalid assumptions about
        addresses).

     X  Untested, but I think it cannot work unless someone builds an X
        proxy, which is probably an external program to the masquerading
        code.  One way of making this work is to use ssh as the link and
        use the internal X proxy of that to make things work!

  4.3.3.  Platforms/OS Tested as on OTHER machines

    Linux

    Solaris

    Windows 95

    Windows NT (both workstation and server)

    Windows For Workgroup 3.11 (with TCP/IP package)

    Windows 3.1 (with Chameleon package)

    Novel 4.01 Server

    OS/2 (including Warp v3)

    Macintosh OS (with MacTCP or Open Transport)

    DOS (with NCSA Telnet package, DOS Trumpet works partially)

    Amiga (with AmiTCP or AS225-stack)

    VAX Stations 3520 and 3100 with UCX (TCP/IP stack for VMS)

    Alpha/AXP with Linux/Redhat

    SCO Openserver (v3.2.4.2 and 5)

    IBM RS/6000 running AIX

    (Anyone tried other platforms?)

  4.4.  IP Firewall Administration (ipfwadm)

  This section provides a more in-depth guide on using ipfwadm.

  This is a setup for a firewall/masquerade system behind a PPP link
  with a static PPP address follows. Trusted interface is 192.168.255.1,
  PPP interface has been changed to protect the guilty :).  I listed
  each incoming and outgoing interface individually to catch IP spoofing
  as well as stuffed routing and/or masquerading. Also anything not
  explicitly allowed is forbidden!

  #!/bin/sh
  #
  # /etc/rc.d/rc.firewall, define the firewall configuration, invoked from
  # rc.local.
  #

  PATH=/sbin:/bin:/usr/sbin:/usr/bin

  # testing, wait a bit then clear all firewall rules.
  # uncomment following lines if you want the firewall to automatically
  # disable after 10 minutes.
  # (sleep 600; \
  # ipfwadm -I -f; \
  # ipfwadm -I -p accept; \
  # ipfwadm -O -f; \
  # ipfwadm -O -p accept; \
  # ipfwadm -F -f; \
  # ipfwadm -F -p accept; \
  # ) &

  # Incoming, flush and set default policy of deny. Actually the default policy
  # is irrelevant because there is a catch all rule with deny and log.
  ipfwadm -I -f
  ipfwadm -I -p deny
  # local interface, local machines, going anywhere is valid
  ipfwadm -I -a accept -V 192.168.255.1 -S 192.168.0.0/16 -D 0.0.0.0/0
  # remote interface, claiming to be local machines, IP spoofing, get lost
  ipfwadm -I -a deny -V your.static.PPP.address -S 192.168.0.0/16 -D 0.0.0.0/0 -o
  # remote interface, any source, going to permanent PPP address is valid
  ipfwadm -I -a accept -V your.static.PPP.address -S 0.0.0.0/0 -D
  your.static.PPP.address/32
  # loopback interface is valid.
  ipfwadm -I -a accept -V 127.0.0.1 -S 0.0.0.0/0 -D 0.0.0.0/0
  # catch all rule, all other incoming is denied and logged. pity there is no
  # log option on the policy but this does the job instead.
  ipfwadm -I -a deny -S 0.0.0.0/0 -D 0.0.0.0/0 -o

  # Outgoing, flush and set default policy of deny. Actually the default policy
  # is irrelevant because there is a catch all rule with deny and log.
  ipfwadm -O -f
  ipfwadm -O -p deny
  # local interface, any source going to local net is valid
  ipfwadm -O -a accept -V 192.168.255.1 -S 0.0.0.0/0 -D 192.168.0.0/16
  # outgoing to local net on remote interface, stuffed routing, deny
  ipfwadm -O -a deny -V your.static.PPP.address -S 0.0.0.0/0 -D 192.168.0.0/16 -o
  # outgoing from local net on remote interface, stuffed masquerading, deny
  ipfwadm -O -a deny -V your.static.PPP.address -S 192.168.0.0/16 -D 0.0.0.0/0 -o
  # outgoing from local net on remote interface, stuffed masquerading, deny
  ipfwadm -O -a deny -V your.static.PPP.address -S 0.0.0.0/0 -D 192.168.0.0/16 -o
  # anything else outgoing on remote interface is valid
  ipfwadm -O -a accept -V your.static.PPP.address -S your.static.PPP.address/32 -D
  0.0.0.0/0
  # loopback interface is valid.
  ipfwadm -O -a accept -V 127.0.0.1 -S 0.0.0.0/0 -D 0.0.0.0/0
  # catch all rule, all other outgoing is denied and logged. pity there is no
  # log option on the policy but this does the job instead.
  ipfwadm -O -a deny -S 0.0.0.0/0 -D 0.0.0.0/0 -o

  # Forwarding, flush and set default policy of deny. Actually the default policy
  # is irrelevant because there is a catch all rule with deny and log.
  ipfwadm -F -f
  ipfwadm -F -p deny
  # Masquerade from local net on local interface to anywhere.
  ipfwadm -F -a masquerade -W ppp0 -S 192.168.0.0/16 -D 0.0.0.0/0
  # catch all rule, all other forwarding is denied and logged. pity there is no
  # log option on the policy but this does the job instead.
  ipfwadm -F -a deny -S 0.0.0.0/0 -D 0.0.0.0/0 -o

  You can block traffic to a particular site using the -I, -O or -F.
  Remember that the set of rules are scanned top to bottom and -a means
  "append" to the existing set of rules so any restrictions need to come
  before global rules. For example (and untested) :-

  Using -I rules. Probably the fastest but it only stops the local
  machines, the firewall itself can still access the "forbidden" site.
  Of course you might want to allow that combination.

  # reject and log local interface, local machines going to 204.50.10.13
  ipfwadm -I -a reject -V 192.168.255.1 -S 192.168.0.0/16 -D 204.50.10.13/32 -o
  # local interface, local machines, going anywhere is valid
  ipfwadm -I -a accept -V 192.168.255.1 -S 192.168.0.0/16 -D 0.0.0.0/0

  Using -O rules. Slowest because the packets go through masquerading
  first but this rule even stops the firewall accessing the forbidden
  site.

  # reject and log outgoing to 204.50.10.13
  ipfwadm -O -a reject -V your.static.PPP.address -S your.static.PPP.address/32 -D
  204.50.10.13/32 -o
  # anything else outgoing on remote interface is valid
  ipfwadm -O -a accept -V your.static.PPP.address -S your.static.PPP.address/32 -D
  0.0.0.0/0

  Using -F rules. Probably slower than -I and this still only stops
  masqueraded machines (i.e. internal), firewall can still get to
  forbidden site.

  # Reject and log from local net on PPP interface to 204.50.10.13.
  ipfwadm -F -a reject -W ppp0 -S 192.168.0.0/16 -D 204.50.10.13/32 -o
  # Masquerade from local net on local interface to anywhere.
  ipfwadm -F -a masquerade -W ppp0 -S 192.168.0.0/16 -D 0.0.0.0/0

  No need for a special rule to allow 192.168.0.0/16 to go to
  204.50.11.0, it is covered by the global rules.

  There is more than one way of coding the interfaces in the above
  rules.  For example instead of -V 192.168.255.1 you can code -W eth0,
  instead of -V your.static.PPP.address you can use -W ppp0. Personal
  choice and documentation more than anything.

  4.5.  IP Masquerade and Demand-Dial-Up

  1. If you would like to setup your network to automatically dial up
     the Internet, the diald demand dial-up package will be of great
     utility.

  2. To setup the diald, please check out the Setting Up Diald for Linux
     Page <http://home.pacific.net.sg/~harish/diald.config.html>

  3. Once diald and IP masq have been setup, you can go to any of the
     client machines and initiate a web, telnet or ftp session.

  4. Diald will detect the incoming request, then dial up your ISP and
     establish the connection.

  5. There is a timeout that will occur with the first connection.  This
     is inevitable if you are using analog modems.  The time taken to
     establish the modem link and the PPP connections will cause your
     client program to timeout.  This can be avoided if you are using an
     ISDN connection.  All you need to do is to terminate the current
     process on the client and restart it.

  4.6.  IPautofw Packet Fowarder

  IPautofw <ftp://ftp.netis.com/pub/members/rlynch/ipautofw.tar.gz> is a
  generic forwarder of TCP and UDP for Linux masquerading.  Generally to
  utilize a package which requires UDP, a specific ip_masq module needs
  to be loaded; ip_masq_raudio, ip_masq_cuseeme, ...  Ipautofw acts in a
  more generic manner, it will forward any type of traffic including
  those which the application specific modules will not forward.  This
  may create a security hole if not administered correctly.

  5.  Miscellaneous

  5.1.  Getting Help

    IP Masquerade Resource page
     <http://www.wwonline.com/~achau/ipmasq/> should have enough
     information for setting up IP Masquerade
     An alternative <http://www.hwy401.com/achau/ipmasq/> site for this
     page

    Joining IP masquerade mailing list (recommended)
     To subscribe, send a mail with subject "subscribe" (no quote) to
     masq-request@indyramp.com
     To unsubscribe, send a mail with subject "unsubscribe" (no quote)
     to masq-request@indyramp.com
     To get help on using the mailing list, send a mail with subject
     "archive help" or "archive dir" (no quote) to masq-
     request@indyramp.com

    IP masquerade mailing list archive
     <http://www.indyramp.com/masq/list/> contains all the past messages
     sent to the mailing list.

    This Linux IP Masquerade mini HOWTO
     <http://www.wwonline.com/~achau/ipmasq/ipmasq-HOWTO.html> for
     kernel 2.x (if you're using a 1.3.x or 2.x kernel)

    IP Masquerade HOWTO for kernel 1.2.x
     <http://www.wwonline.com/~achau/ipmasq/ipmasq-HOWTO-1.2.x.txt> if
     you're using an older kernel

    IP masquerade FAQ <http://www.indyramp.com/masq/ip_masquerade.txt>
     has some general information

    X/OS Ipfwadm page <http://www.xos.nl/linux/ipfwadm/> contains
     sources, binaries, documentation, and other information about the
     ipfwadm package

    LDP Network Administrator's Guide
     <http://linuxwww.db.erau.edu/NAG/> is a must for beginners trying
     to set up a network

    Linux NET-2 HOWTO
     <http://www.caldera.com/LDP/HOWTO/NET-2-HOWTO.html> also has lots
     of useful information about Linux networking

    Linux ISP Hookup HOWTO <http://www.caldera.com/LDP/HOWTO/ISP-
     Hookup-HOWTO.html> and Linux PPP HOWTO
     <http://www.caldera.com/LDP/HOWTO/PPP-HOWTO.html> gives you
     information on how to connect your Linux host to the Internet

    Linux Ethernet-Howto <http://www.caldera.com/LDP/HOWTO/Ethernet-
     HOWTO.html> is a good source of information about setting up a LAN
     running ethernet

    You may also be interested in Linux Firewalling and Proxy Server
     HOWTO <http://www.caldera.com/LDP/HOWTO/Firewall-HOWTO.html>

    Linux Kernel HOWTO <http://www.caldera.com/LDP/HOWTO/Kernel-
     HOWTO.html> will guide you through the kernel compilation process

    Other Linux HOWTOs <http://www.caldera.com/LDP/HOWTO/HOWTO-
     INDEX-3.html> such as Kernel HOWTO

    Posting to the USENET newsgroup: comp.os.linux.networking

  5.2.  Thanks to

    Gabriel Beitler, gbeitler@aciscorp.com
     on providing section 3.3.8 (setting up Novel)

    Ed Doolittle, dolittle@math.toronto.edu
     on suggestion to -V option in ipfwadm command for improved security

    Matthew Driver, mdriver@cfmeu.asn.au
     on helping extensively on this HOWTO, and providing section 3.3.1
     (setting up Windows 95)

    Ken Eves, ken@eves.com
     on the FAQ that provides invaluable information for this HOWTO

    Ed. Lott, edlott@neosoft.com
     for a long list of tested system and software

    Nigel Metheringham, Nigel.Metheringham@theplanet.net
     on contributing his version of IP Packet Filtering and IP
     Masquerading HOWTO, which make this HOWTO a better and technical
     in-depth document
     section 4.1, 4.2, and others

    Keith Owens, kaos@ocs.com.au
     on providing an excellent guide on ipfwadm section 4.2
     on correction to ipfwadm -deny option which avoids a security hole,
     and clarified the status of ping over ip_masq

    Rob Pelkey, rpelkey@abacus.bates.edu
     on providing section 3.3.6 and 3.3.7 (setting up MacTCP and Open
     Transport)

    Harish Pillay, h.pillay@ieee.org
     on providing section 4.5 (dial-on-demand using diald)

    Mark Purcell, purcell@rmcs.cranfield.ac.uk
     on providing section 4.6 (IPautofw)

    John B. (Brent) Williams, forerunner@mercury.net
     on providing section 3.3.7 (setting up Open Transport)

    Enrique Pessoa Xavier, enrique@labma.ufrj.br
     on the bootp setup suggestion

    developers of IP Masquerade for this great feature

         Delian Delchev, delian@wfpa.acad.bg

         Nigel Metheringham, Nigel.Metheringham@theplanet.net

         Keith Owens, kaos@ocs.com.au

         Jeanette Pauline Middelink, middelin@polyware.iaf.nl

         David A. Ranch, trinity@value.net

         Miquel van Smoorenburg, miquels@q.cistron.nl

         Jos Vos, jos@xos.nl

    all users sending feedback and suggestion to the mailing list,
     especially the ones who reported errors in the document and the
     clients that are supported and not supported

  5.3.  Reference

    IP masquerade FAQ by Ken Eves

    IP masquerade mailing list archive by Indyramp Consulting

    Ipfwadm page by X/OS

    Various networking related Linux HOWTOs

