dranch@trinnet.net
November 13, 2005
This document describes how to enable the Linux IP Masquerade feature on a given Linux host. IP Masquerade is a form of Network Address Translation or NAT which NAT allows internally connected computers that do not have one or more registered Internet IP addresses to communicate to the Internet via the Linux server's Internet IP address.
This document describes how to enable the Linux IP Masquerade feature on a given Linux host. IP Masquerade, called "IPMASQ" or "MASQ" for short, is a form of Network Address Translation (NAT) which allows internally connected computers that do not have one or more registered Internet IP addresses to communicate to the Internet via the Linux server's Internet IP address. Since IPMASQ is a generic technology, you can connect the Linux server's internal and external to other computers through LAN technologies like Ethernet, TokenRing, and FDDI, as well as dialup connections line PPP or SLIP links. This document primarily uses Ethernet and PPP connections in examples because it is most commonly used with DSL / Cablemodems and dialup connections.
"This document is intended for systems running stable Linux kernels like 2.4.x, 2.2.x, and 2.0.x preferably on an IBM-compatible PC. IP Masquerade does work on other Linux-supported platforms like Sparc, Alpha, PowerPC, etc. but this HOWTO doesn't cover them in as much detail. Beta kernels such as 2.5.x, 2.3.x, 2.1.x, and ANY kernels less than 2.0.x are NOT covered in this document. The primary reason for this is because many of the older kernels are considered broken. If you are using an older kernel version, it is highly advisable to upgrade to one of the stable Linux kernels before using IP Masquerading. "
From the original IPMASQ HOWTO author:
"As a new user, I found it very confusing to setup IP masquerade on the Linux kernel, (back then, its was a 1.2.x kernel). Although there was a FAQ and a mailing list, there was no documentation dedicated to this. There was also some requests on the mailing list for a HOWTO manual. So, I decided to write this HOWTO as a starting point for new users and possibly create a building block for other knowledgeable users. If you, the reader, have any additional ideas, corrections, or questions about this document, please feel free to contact us. "
This document was originally written by Ambrose Au back in August, 1996, based on the 1.x kernel IPMASQ FAQ written by Ken Eves and numerous helpful messages from the original IP Masquerade mailing list. In particular, a mailing list message from Matthew Driver inspired Ambrose to set up IP Masquerade and eventually write version 0.80 of this HOWTO. In April 1997, Ambrose created the Linux IP Masquerade Resource Web site at http://ipmasq.webhop.net which has provided up-to-date information on Linux IP Masquerading ever since. In February 1999, David Ranch took over maintenance of the HOWTO. David then re-wrote the HOWTO and added a substantial number of sections to the document. Today, the HOWTO is still maintained by David where he constantly updates it and fixes any reported bugs, etc.
Please feel free to send any feedback or comments regarding this HOWTO to dranch@trinnet.net if you have any corrections or if any information/URLs/etc. is missing. Your invaluable feedback will certainly influence the future of this HOWTO!
This HOWTO is meant to be a fairly comprehensive guide to getting your Linux IP Masquerading system working in the shortest time possible. David only plays a technical writer on T.V. so you might find the information in this document not as general and/or objective as it could be. If you think a section could be clearer, etc.. please let David know. The latest version of the MASQ HOWTO can be found at Dranch's Linux Page. Additional news, mirrors of the HOWTO, and information regarding IPMASQ can be found at the IP Masquerade Resource web page. If you have any technical questions on IP Masquerade, please join the IP Masquerade Mailing List instead of sending email to David or Ambrose. Most MASQ problems are -common- for ALL MASQ users and can be easily solved by users on the list. In addition to this, the response time of the IP MASQ email list will be much faster than a reply from either David or Ambrose.
The latest version of this document can be found at the following sites which also contains HTML, Postscript, PDF, etc. versions
This document is copyrighted(c) 2003,2002,2001,2000 for David A. Ranch and it is a FREE document. You may redistribute it under the terms of the GNU General Public License (GPL).
The information herein this document is, to the best of David's knowledge, correct. However, the Linux IP Masquerade feature is written by humans and thus, the chance of mistakes, bugs, etc. might occur from time to time.
No person, group, or other body is responsible for any damage on your computer(s) and any other losses by using the information on this document. i.e.
"THE AUTHORS AND ALL MAINTAINERS ARE NOT RESPONSIBLE FOR ANY DAMAGES INCURRED DUE TO ACTIONS TAKEN BASED ON THE INFORMATION IN THIS DOCUMENT. "
Ok, with all this behind us... On with the show..
IP Masquerade is a networking function in Linux similar to the one-to-many (1:Many) NAT (Network Address Translation) servers found in many commercial firewalls and network routers. For example, if a Linux host is connected to the Internet via PPP, Ethernet, etc., the IP Masquerade feature allows other "internal" computers connected to this Linux box (via PPP, Ethernet, etc.) to also reach the Internet as well. Linux IP Masquerading allows for this functionality even though these internal machines don't have an officially assigned IP address.
MASQ allows a set of machines to invisibly access the Internet via the MASQ gateway. To other machines on the Internet, the outgoing traffic will appear to be from the IP MASQ Linux server itself. In addition to the added functionality, IP Masquerade provides the foundation to create a HEAVILY secured networking environment. With a well built firewall, breaking the security of a well configured masquerading system and internal LAN should be considerably difficult to accomplish.
If you would like to know more on how MASQ (1:Many) differs from 1:1 (true) NAT and Proxy solutions, please see the Section 7.6 FAQ entry.
IP Masquerade has been in the Linux kernels for several years now and is quite mature as the kernel enters the 2.4.x stage. Kernels since Linux 1.3.x have had MASQ support built-in. Today, many individuals and commercial businesses are using it with excellent results.
2.4.x kernel users:
The 2.4.x kernel hosts an entirely re-written set of NAT code which is both far superior, faster, and more secure than any previous versions written for Linux. Unfortunately, several kernel modules that were written for the 2.2.x kernel to support things like UDP-based RealAudio, etc. have not been ported to 2.4.x yet. Because of this, some people should consider NOT upgrading if these network applications are critical to them. But, at the same time, some of these programs have been updated and now use different, NAT-friendly protocols. Thus special NAT treatment is no longer required. As always, please see the http://ipmasq.webhop.net/: The IP Masquerade Resources site for updated news, etc.
Common network functionalities like Web browsing, telnet, ssh, ping, traceroute, etc. work well over stock IP Masquerade setups. Other network applications such as ftp, irc, and Real Audio work well with the appropriate additional IP MASQ modules loaded into the kernel as modules. Other network-specific programs like streaming audio (MP3s, True Speech, etc) should work too without any special module. Some users on the mailing list also had good results with video conferencing software.
It should be noted that running IP Masquerade with only ONE network card (NIC) to MASQ between internal and external Ethernet networks is NOT recommended. For more details, please see Section 7.28 FAQ section.
Anyways, please refer to Section 6.3 for a more complete listing of software supported by IP Maquerade all kernel versions.
IP Masquerade works well as a server to other 'client machines' running various operating systems and hardware platforms. Here is a sampling of successful reports with internal MASQed systems running :
UNIX: Sun Solaris, [Net,Free,Open,*i]-BSD, Hp-UX, Linux, IBM AIX, Digital UNIX, Ultrix, etc.
Microsoft Windows 2000, NT (3.x and 4.x), 95/98/ME, Windows for Workgroups (with the TCP/IP package)
IBM OS/2
Apple Macintosh MacOS machines running either MacTCP or Open Transport
DOS-based systems with packet drivers and the NCSA Telnet package
VAXen
Compaq/Digital Alpha running Linux and NT
Amiga computers with AmiTCP or AS225-stack.
The list goes on and on but the point is, if your OS platform talks TCP/IP, it should work with Linux's IP Masquerade!
If you have a Linux host connected to the Internet and..
if you have internal computers running TCP/IP connected that are connected to this Linux box via on a network, and/or
if your Linux host has more than one modem and acts as a PPP or SLIP server connected to other computers, and these machines do not have official or public assigned IP addresses (i.e. addressed with private TCP/IP numbers).
If you want those OTHER machines to communicate to the Internet without spending extra money to acquire additional Public / Official TCP/IP addresses from your ISP, then you should either configure Linux to be a router or purchase an external router.
If your machine is a stand-alone Linux host connected to the Internet (setting up a firewall is a good idea though), or
if you already have multiple assigned public addresses for your OTHER machines, and
if you don't like the idea of a 'free ride' using Linux and feel more comfortable using expensive commercial tools to perform the exact same functionalities.
Based from the original IP Masquerade FAQ by Ken Eves: Here is a drawing of the most simplistic setup:
PPP/ETH/etc. +------------+ +-------------+
to ISP provider | Linux #1 | PPP/ETH/etc. | Anybox |
| | | |
<---------- modem1| |modem2 ----------- modem3| |
| | | |
111.222.121.212 | | 192.168.0.100 | |
+------------+ +-------------+ |
In the above drawing, a Linux box with IP_MASQUERADING is installed as Linux #1 and is connected to the Internet via PPP, Ethernet, etc. It has an assigned public IP address of 111.222.121.212. It also has another network interface (e.g. modem2) connected to allow incoming network traffic be it from a PPP connection, Ethernet connection, etc.
The second system (which does not need to be Linux) connects into the Linux #1 box and starts its network traffic to the Internet. This second machine does NOT have a publicly assigned IP address from the Internet, so it uses an RFC1918 private address, say 192.168.0.100. (see below for more info)
With IP Masquerade and the routing configured properly, this second machine "Anybox" can interact with the Internet as if it was directly connected to the Internet with a few small exceptions [noted later].
Quoting Pauline Middelink (the founder of Linux's IPMASQ):
"Do not forget to mention that the "ANYBOX" machine should have the Linux #1 box configured as its default gateway (whether it be the default route or just a subnet is no matter). If the "ANYBOX" machine is connected via a PPP or SLIP connection, the Linux #1 machine should be configured to support proxy arp for all routed addresses. But, the setup and configuration of proxy arp is beyond the scope of this document. Please see the PPP-HOWTO for more details."
The following is an excerpt on how IPMASQ briefly works though this will be explained in more detail later. This short text is based from a previous 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 PPP or Ethernet connected Linux box is its
gateway.
o When a packet comes into the Linux box from ANYBOX, it will assign the
packet to a new TCP/IP source port number and insert its own IP address
inside the packet header, saving the originals. The MASQ server will
then send the modified packet over the PPP/ETH interface onto the
Internet.
o When a packet returns from the Internet into the Linux box, Linux
examines if the port number is one of those ports that was assigned
above. If so, the MASQ server will then take the original port and
IP address, put them back in the returned packet header, and send
the packet to ANYBOX.
o The host that sent the packet will never know the difference. |
Another IP Masquerading Example:
A typical example is given in the diagram below:
Ethernet
192.168.0.x
+----------+
| |
| A-box |::::::
| |.2 :
+----------+ :
: +----------+ PPP/ETH
+----------+ : .1 | Linux | link
| | :::::::| Masq-Gate|:::::::::::::::::::>> Internet
| B-box |:::::: | | 111.222.121.212
| |.3 : +----------+
+----------+ :
:
+----------+ :
| | :
| C-box |::::::
| |.4
+----------+
| | | >
| <-Internal Network--> | | <- External Network ----> >
| connected via an | | Connected from the >
| Ethernet hub or | | Linux server to your >
| switch | | Internet connection > |
In this example, there are (4) computer systems that we are concerned about. There is also presumably something on the far right that your PPP/ETH connection to the Internet comes through (modem server, DSL DSLAM, Cablemodem router, etc.). Out on the Internet, there exists some remote host (very far off to the right of the page) that you are interested in communicating with). The Linux system named Masq-Gate is the IP Masquerading gateway for ALL internal networked machines. In this example, the machines A-box, B-box, and C-box would have to go through the Masq-Gate to reach the Internet. The internal network uses one of several RFC-1918 assigned private network addresses, where in this case, would be the Class-C network 192.168.0.0. If you aren't familiar with RFC1918, it is encouraged to read the first few chapters of the RFC but the jist of it is that the TCP/IP addresses 10.0.0.0/8, 172.16-31.0.0/12, and 192.168.0.0/16 are reserved. When we say "reserved", we mean that anyone can use these addresses as long as they aren't routed over the Internet. ISPs are even allowed to use this private addressing space as long as they keep these addresses within their own networks and NOT advertise them to other ISPs. Unfortunately, this isn't always the case but thats beyond the scope of this HOWTO.
Anyway, the Linux box in the diagram above has the TCP/IP address 192.168.0.1 while the other systems has the addresses:
A-Box: 192.168.0.2
B-Box: 192.168.0.3
C-Box: 192.168.0.4
The three machines, A-box, B-box and C-box, can have any one of several operating systems, just as long as they can speak TCP/IP. Some such as Windows 95, Macintosh MacTCP or OpenTransport , or even another Linux box have the ability to connect to other machines on the Internet. When running the IP Masquerade, the masquerading system or MASQ-gate converts all of these internal connections so that they appear to originate from the masq-gate itself. MASQ then arranges so that the data coming back to a masqueraded connection is relayed to the proper originating system. Therefore, the systems on the internal network are only able to see a direct route to the internet and are unaware that their data is being masqueraded. This is called a "Transparent" connection.
NOTE: Please see Chapter 7 for more details on topics such as:
The differences between NAT, MASQ, and Proxy servers.
How packet firewalls work
" ** Please refer to IP Masquerade Resource for the latest information. ** "
The newest 2.4.x kernels are now using both a completely new TCP/IP network stack as well as a new NAT sub-system called NetFilter. Within this NetFilter suite of tools, we now have a tool called IPTABLES for the 2.4.x kernels much like there was IPCHAINS for the 2.2.x kernels and IPFWADM for the 2.0.x kernels. The new IPTABLES system is far more powerful (combines several functions into one place like true NAT functionality), offers better security (stateful inspection), and better performance with the new 2.4.x TCP/IP stack. But this new suite of tools can be a bit complicated in comparison to older generation kernels. Hopefully, if you follow along with this HOWTO carefully, setting up IPMASQ won't be too bad. If you find anything unclear, downright wrong, etc. please email David about it.
Unlike the migration to IPCHAINS from IPFWADM, the new NetFilter tool has kernel modules that can actually support older IPCHAINS and IPFWADM rulesets with minimal changes. So re-writing your old MASQ or firewall ruleset scripts is not longer required. BUT.. with the 2.4.x kernels, you cannot use the old 2.2.x MASQ modules like ip_masq_ftp, ip_masq_irc, etc. AND IPCHAINS is incompatible with the new IPTABLES modules like ip_conntrack_ftp, etc. So, what does this mean? It basically means that if you want to use IPMASQ or PORTFW functionality under a 2.4.x kernel, you shouldn't use IPCHAINS rules but IPTABLES ones instead. Please also keep in mind that there might be several benefits in performing a full ruleset re-write to take advantage of the newer IPTABLES features like stateful tracking, etc. but that is dependant upon how much time you have to migrate your old rulesets. Please see Section 7.40 for additional details.
Some new 2.4.x functionalities include the following:
PROs:
Lots of new protocols modules like: amanda, eggdrop, ipsec, ipv6, portscan, pptp, quota, rsh, talk, and tftp
TRUE 1:1 NAT functionality for those who have TCP/IP addresses and subnets to use (no more iproute2 commands)
Stateful application level (FTP, IRC, etc.) and stateful protocol level (TCP/UDP/ICMP) network traffic inspection
Built-in PORT Forwarding (no more ipmasqadm or ipportfw commands)
The built-in PORTFW'ing support works for both external and internal traffic. This means that users that have PORTFW for external traffic and REDIR for internal port redirection do not need to use two tools any more!
PORT Forwarding of FTP traffic to internal hosts is now completely supported and is handled in the conn_trak_ftp module
Full Policy-Based routing features (source-based TCP/IP address routing)
Compatibility with Linux's FastRoute feature for significantly faster packet forwarding (a.k.a Linux network switching).
Note that this feature is still not compatible with packet filtering for strong firewall rulesets.
Fully supports TCP/IP v4, v6, and even DECnet (ack!)
Supports wildcard interface names like "ppp*" for serial interfaces like ppp0, ppp1, etc
Supports filtering on both input and output INTERFACES (not just IP addresses)
Source Ethernet MAC filtering
Denial of Service (DoS) packet rate limiting
Packet REJECTs now have user-selectable return ICMP messages
Variable levels of logging (different packets can go to different SYSLOG levels)
Other features like traffic mirroring, securing traffic per login, etc.
CONs:
Netfilter is an entirely new architechure thus most of the older 2.2.x MASQ kernel modules written to make non-NAT friendly network applications work through IPMASQ need to be re-written for the 2.4.x kernels. Because of this, if you specifically need functionality from some of these modules (see below), you should stay with a 2.2.x kernel until these modules have been either ported or the application has been updated to use NAT-friendly protocols. If you are curious on the porting status of a given module, please email the author of the module and NOT David or Ambrose. We don't code.. we just document. :-)
Here is the status of the known IP Masq kernel modules or patches as found on the IPMASQ WWW site's Application Support Matrix. In addition, you should also setup out the Netfilter Patch-o-Matic URL as well. If you have the time and knowledge to help in the porting of code, your efforts would be highly appreciated:
Status = Module name = Description and notes
--------- ----------- ----------------------------------
Ported CuSeeme Used for Video conferencing
NotPorted DirectPlay Used for online Microsoft-based games
Ported FTP Used for file transfers
- NOTEs: Built into the kernel and
fully supports PORTFWed FTP
ReWritten H.323 Used for Video conferencing
NotPorted ICQ Used for Instant messaging
* No longer required for modern ICQ clients
Ported Irc Used for Online chat rooms
Ported Quake Used for online Quake games
Ported PPTP Allow for multiple clients to the same server
NotPorted Real Audio Used for Streaming video / audio
* No longer required for modern RealVideo clients
NotPorted VDO Live Used for Streaming audio? |
Documentation on how to perform MASQ module porting is available at http://www.netfilter.org/documentation/HOWTO/netfilter-hacking-HOWTO.html. If you have the time and knowledge, your talent would highly be appreciated in porting these modules.
If you'd like to read up more on NetFilter and IPTables, please see: http://www.netfilter.org/documentation/index.html#HOWTO and more specifically http://www.netfilter.org/documentation/HOWTO//NAT-HOWTO.html
Linux 2.4.x IP Masquerade requirements include:
Any decent computer hardware. See Section 7.2 for more details.
The 2.4.x kernel source is available from http://www.kernel.org/.
NOTE: Most modern Linux distributions, Section 7.1, that natively come with 2.4.x kernels are typically modular kernels and have all the IP Masquerade functionality already included. In such cases, there is no need to compile a new Linux kernel. If you are UPGRADING your kernel, you should be aware of other programs that might be required and/or need to be upgraded as well (mentioned later in this HOWTO).
The program "iptables" version 1.2.4 or newer ( 1.2.7a or newer is highly recommended ) archive available from http://www.netfilter.org/
NOTE #1: All versions of IPTABLES less than 1.2.3 have a FTP module issue that can bypass any existing firewall rulesets. ALL IPTABLES users are highly recommended to upgrade to the newest version. The URL is above.
NOTE #2: All versions of IPTABLES less than 1.2.2 have a FTP "port" security vulnerability in the ip_conntrack_ftp module. All IPTABLES users are highly recommended to upgrade to the newest version. The URL is above.
This tool, much like the older IPCHAINS and IPFWADM tools enables the various Masquerding code, more advanced forms of NAT, packet filtering, etc. It also makes use of additional MASQ modules like the FTP and IRC modules. Additional information on version requirements for the newest IPTABLES howto, etc. is located at the Unreliable IPTABLES HOWTOs page.
Loadable kernel modules, preferably 2.1.121 or higher, are available from http://home.pi.se/blox/modutils/index.html or ftp://ftp.kernel.org/pub/linux/utils/kernel/modutils
A properly configured and running TCP/IP network running on the Linux machine as covered in Linux NET HOWTO and the Network Administrator's Guide . Also check out the TrinityOS document which is also authored by David Ranch. TrinityOS is a very comprehensive guide for Linux networking. Some topics include IP MASQ, security, DNS, DHCP, Sendmail, PPP, Diald, NFS, IPSEC-based VPNs, and performance sections, to name a few. There are over Fifty sections in all!
Connectivity to the Internet for your Linux host covered in Linux ISP Hookup HOWTO, Linux PPP HOWTO, and TrinityOS. Other helpful HOWTOs could include: Linux DHCP mini-HOWTO, Linux Cable Modem mini-HOWTO and http://www.tldp.org/HOWTO/DSL-HOWTO/index.html
Know how to configure, compile, and install a new Linux kernel as described in the Linux Kernel HOWTO. This HOWTO does cover kernel compiling but only for IP Masquerade related options.
" ** Please refer to IP Masquerade Resource for the latest information. ** "
Any decent computer hardware. See Section 7.2 for more details.
The 2.2.x kernel source is available from http://www.kernel.org/.
NOTE: Most modern Linux distributions, Section 7.1, that natively come with 2.2.x kernels are typically modular kernels and have all the IP Masquerade functionality already included. In such cases, there is no need to compile a new Linux kernel. If you are UPGRADING your kernel, you should be aware of other programs that might be required and/or need to be upgraded as well (mentioned later in this HOWTO).
NOTE #1: --- UPDATE YOUR KERNEL --- Linux 2.2.x kernels less than version 2.2.20 contain several different security vulnerabilities (some were MASQ specific). Kernels less than 2.2.20 have a few local vulnerabilities. Kernel versions less than 2.2.16 have a TCP root exploit vulnerability and versions less than 2.2.11 have a IPCHAINS fragmentation bug. Because of these issues, users running a firewall with strong IPCHAINS rulesets are open to possible instrusion. Please upgrade your kernel to a fixed version.
NOTE #2: Some newer Section 7.1 such as Redhat 5.2 might not be Linux 2.2.x ready (upgradable). Tools like DHCP, NetUtils, etc. will need to be upgraded. More details can be found later in the HOWTO.
Loadable kernel modules, preferably 2.1.121 or higher, are available from http://home.pi.se/blox/modutils/index.html or ftp://ftp.kernel.org/pub/linux/utils/kernel/modutils
A properly configured and running TCP/IP network running on the Linux machine as covered in Linux NET HOWTO and the Network Administrator's Guide . Also check out the TrinityOS document which is also authored by David Ranch. TrinityOS is a very comprehensive guide for Linux networking. Some topics include IP MASQ, security, DNS, DHCP, Sendmail, PPP, Diald, NFS, IPSEC-based VPNs, and performance sections, to name a few. There are over Fifty sections in all!
Connectivity to the Internet for your Linux host covered in Linux ISP Hookup HOWTO, Linux PPP HOWTO, and TrinityOS. Other helpful HOWTOs could include: Linux DHCP mini-HOWTO, Linux Cable Modem mini-HOWTO and http://www.tldp.org/HOWTO/DSL-HOWTO/index.html
IP Chains 1.3.10 or newer are available from http://www.netfilter.org/ipchains/. Additional information on version requirements for the newest IPCHAINS HOWTO, etc is located at the Linux IP Chains page (mirror at Samba.org)
Know how to configure, compile, and install a new Linux kernel as described in the Linux Kernel HOWTO. This HOWTO does cover kernel compiling but only for IP Masquerade related options.
Other optional patches and tools for 2.2.x kernels
TCP/IP port-forwarding or re-directing:
PORTFW FTP Solutions:
There are 2.2.x and 2.0.x kernel MASQ Module solutions for PORTFWed FTP to a MASQed machine (put an FTP server behind a MASQ server). Please see the Application Page on the IPMASQ WWW site for full details. Please note that this is not required for 2.4.x kernels.
There is a full FTP proxy application from SuSe that will also allow PORTFWed-like functionality to reach an internal FTP server. For more details, please refer to the SuSe Proxy URL.
IPROUTE2 for True 1:1 NAT, Policy-based (source) routing, and Traffic Shaping:
Documentation can be found at http://www.compendium.com.ar/policy-routing.txt
Some source code mirrors are at:
ftp://ftp.funet.fi/pub/mirrors/ftp.inr.ac.ru/ip-routing/ (STM1 to USA) --- ftp://sunsite.icm.edu.pl/pub/Linux/iproute/
ftp://ftp.sunet.se/pub/Linux/ip-routing/ --- ftp://ftp.nvg.ntnu.no/pub/linux/ip-routing/
ftp://ftp.crc.ca/pub/systems/linux/ip-routing/ --- ftp://ftp.paname.org (France)
Please see the IP Masquerade Resource page for more information available on these patches and possibly others as well.
" ** Please refer to IP Masquerade Resource for the latest information. ** "
Any decent computer hardware. See Section 7.2 for more details.
The 2.0.x kernel source is available from http://www.kernel.org/.
NOTE: Most modern Linux Section 7.1 that natively come with 2.0.x kernels are typically modular kernels and have all the IP Masquerade functionality already included. In such cases, there is no need to compile a new Linux kernel. If you are UPGRADING your kernel, you should be aware of other programs that might be required and/or need to be upgraded as well (mentioned later in this HOWTO).
Loadable kernel modules, preferably 2.1.85 or newer is available from http://home.pi.se/blox/modutils/index.html or ftp://ftp.kernel.org/pub/linux/utils/kernel/modutils (modules-1.3.57 is the minimal requirement)
A properly configured and running TCP/IP network running on the Linux machine as covered in Linux NET HOWTO and the Network Administrator's GuideAlso check out the TrinityOS document which is also authored by David Ranch. TrinityOS is a very comprehensive guide to Linux networking. Topics include IP MASQ, security, DNS, DHCP, Sendmail, PPP, Diald, NFS, IPSEC-based VPNs, performance issues, and many more. There exists over fifty sections in all!
Connectivity to the Internet for your Linux host is covered in Linux ISP Hookup HOWTO, Linux PPP HOWTO, and TrinityOS. Other helpful HOWTOs could include: Linux DHCP mini-HOWTO, Linux Cable Modem mini-HOWTO and Linux DSL HOWTO
Ipfwadm 2.3.0 or newer is available from http://www.xos.nl/linux/ipfwadm/download.html
More information on version requirements are on the Linux IPFWADM page
If you are interested in running IPCHAINS on a 2.0.x+ kernel, see Willy Tarreau's IPCHAINS enabler for 2.0.36+ or Rusty's IPCHAINS for 2.0.x kernels. Please note that these patches are NOT compatible with the IPPORTFW patches for the 2.0.x kernels. Unfortunately, its an either/or deal.
Know how to configure, compile, and install a new Linux kernel as described in the Linux Kernel HOWTO. This HOWTO does cover kernel compiling but only for IP Masquerade related options.
Here is a list of IP Masquerading patches for 2.0.x kernels:
Steven Clarke's IP PortForwarding (IPPORTFW) - RECOMMENDED
REDIR for TCP (REDIR) - NOT Recommended unless required for internal PORTFW
UDP redirector (UDPRED) - NOT Recommended
PORTFWed FTP:
If you are going to port forward FTP traffic to an internal FTP server, you might need to download Fred Viles's FTP server patch The reason for "might" is that some users have had success without the use of these pathches, while others need it. Explicit details on this topic can be found in Section 6.7 of this HOWTO.
X-Windows display forwarders:
PPTP (GRE) and SWAN (IPSEC) VPNs tunneling forwarders:
If you plan connecting an internal MASQed PC to a remote PPTP server, you MUST INSTALL the PPTP-Masquerade kernel patch available from the URLsbelow. If you plan on having external PPTP users connect to an internal masqueraded PPTP server, not only do you need the kernel patch installed but you also need PORTFW support enabled in the kernel. Please see the following URLs for the patches and more information:
John Hardin's VPN Masquerade forwarders or the old patch for just PPTP Support.
Game specific patches:
Glenn Lamb's LooseUDP for 2.0.36+ patch.
If your private network contains any vital information, think carefully in terms of SECURITY before implementing IP Masquerade. By default, IP MASQ becomes a GATEWAY for you to get onto the Internet, but it also can allow someone from the Internet to possibly get into your internal network.
Once you have IP MASQ functioning, it is HIGHLY recommended for the user to implement a STRONG IPFWADM/IPCHAINS firewall ruleset. Please see Section 6.4.1, Section 6.4.2 and Section 6.4.3 located below for more details.
Almost ALL modern Linux distributions come MASQ-Ready these days but its always good to check your system before you try to set things up. Follow these few steps for your kernel to see if your kernel is MASQ ready.
To see which kernel your system is running, run the following command:
uname -a |
Just for clarity: 2.4.x kernels run IPTABLES :: 2.2.x kernels run IPCHAINS :: 2.0.x kernels run IPFWADM
In general, you must have kernel support for:
IP forwarding
IP masquerading
IP Firewalling
etc.
You will also need to have most MASQ-related modules compiled (most modular kernels will already have all you need already done. Then you will NOT need to re-compile the kernel. If you AREN'T SURE if your Linux distribution is MASQ ready, do the following:
2.4.x kernels (look for most of the following entries out of the much longer list):
Run the command "ls /proc/sys/net/ipv4" while logged into the Linux box. These items are required and should be present regardless if your kernel built IPMASQ as modules or statically.
ip_dynaddr
ip_forward
To check if IPMASQ was compiled statically into the kernel, run the command "/sbin/lsmod" and see if and modules like the ones shown below for the MODULE section are loaded. No? Ok, now run the command "ls /proc/net/" and see if you see additional /proc files such as:
ip_masquerade
ip_conntrack
ip_tables_names
If your kernel uses IPTABLES via modules, most of the stuff listed above should have been missing (because the modules probably aren't loaded). Run the command "ls /lib/modules/`uname -r`/kernel/net/ipv4/netfilter/" where you should see files like:
ip_conntrack.o, ip_conntrack_ftp.o, ip_conntrack_irc.o, ip_nat_ftp.o, ip_nat_irc.o
ip_tables.o, ipt_MASQUERADE.o, iptable_nat.o, iptable_mangle.o, iptable_filter.o
And some optional ones like: ipchains.o, ipt_REJECT.o, and ipt_tcpmss.o
2.2.x kernels (look for most of the following entries out of the much longer list): list):
Run the command "ls /proc/sys/net/ipv4" while logged into the Linux box. These items are required and should be present regardless if your kernel built IPMASQ as modules or statically.
ip_always_defrag
ip_dynaddr
ip_forward
ip_masq_debug
ip_masq_udp_dloose (some distros don't support this -- ignore it for now
Other 2.2.x options can be checked by running "ls /proc/net/"
ip_fwchains
ip_fwnames
ip_masquerade
Even more 2.2.x options can be checked by running "ls /proc/net/"
app
icmp
icq
mfw
portfw
tcp
udp/
2.0.x kernels (look for most of the following entries out of the much longer list):
Run the command "ls /proc/sys/net/ipv4" while logged into the Linux box. These items are required and should be present regardless if your kernel built IPMASQ as modules or statically.
ip_dynaddr
ip_forward
running "ls /proc/net"
ip_forward
ip_masq_app
ip_masquerade
ip_portfw
Ultimately, it comes down to the fact if you see /proc files such as "iip_forward", "ip_masq_debug", "ip_masq_udp_dloose"(optional), and "ip_always_defrag" (optional) exist.
So. Do most of the above /proc entries or kernel modules show up for your respective kernel? If so, thats good! If you cannot find any of the above entries or if you aren't sure if your distribution supports IP Masquerading by default, ASSUME IT DOESN'T SUPPORT MASQ. You can do one last check by looking at the Section 7.1 section and see if your Linux Distribution is listed. Still not there? Sounds like you'll need to compile a kernel but don't worry.. it isn't hard.
Regardless if your current kernel has MASQ support or not, reading the remainder of this section is still highly recommended as it contains other useful information.
First, you'll need to get some 2.4.x kernel sources (preferably the latest kernel version - NEWER *IS* BETTER IN LINUX LAND)
NOTE #1: As both the 2.4.x kernel train and the iptables program development progresses, the compile configurion options will change over time. As of this version of the IPMASQ howto, this section reflects the settings for IPTABLES 1.2.7a and the 2.4.20 kernel. If you are compiling against a newer or previous kernel or IPTABLES version, the dialogs and even commands might look different. It is recommended that you update to the newest versions of both the kernel and IPTABLES for added capability, performance, and stability of the kernel.
Next, depending on the version of the Linux kernel and IPTABLES archive you downloaded, you might want to apply some IPTABLES "patch-o-matic" patches against the kernel. These OPTIONAL patches might fix some known problems, add additional functionality you might need (H.323 protocol, specific issues with network games), etc. It should be noted that the Patch-O-Matic patches used to come with the IPTABLES archive. This is no longer the case and you have to download them (if any) seperately. You can find the the various URLs for downloading IPTABLES, the Patch-o-matic system, etc. Section 2.6.
If this is your first time compiling the kernel, don't be scared. In fact, it's rather easy and it's covered in several URLs found in Section 2.6. Please note that the instructions included here is just one way to do build a kernel. Please see the Kernel HOWTO for full details.
NOTE: Please notice that it IS NOT recommended to put the new kernel sources into the /usr/src/linux directory. You should leave the original kernel sources that came with your Linux distribution in /usr/src/linux. For more details on this topic, please read the "README" file in the top level directory of the kernel sources.
For this HOWTO example, create a directory called /usr/src/kernel. Next, "cd" into this directory and download the newest 2.4.x kernel sources into it. Once downloaded, issue the following command (if the file ends in a .tar.gz): tar xvzf linux-2.4.x.tar.gz or (if the file ends in a .tar.bzip2): tar xyvf linux-2.4.x.tar.bz2. Please substitute the "x" in the 2.4.x filename with the Linux 2.4 kernel version you downloaded.
BZ2 Note: Some Linux distributions use the "I" option instead of the "y" option to decompress bzip2 archives.
Once uncompressed, I recommend that you rename the directory from the stock "linux" name to "linux-2.4.x" (replace the "x" with the specific version of your newly installed kernel) for clarity. To do this, run the command "mv linux linux-2.4.x". Next, make sure there is a directory or symbolic link pointing to "/usr/src/kernel/linux" ie. run the command:
ln -s /usr/src/kernel/linux-2.4.x /usr/src/kernel/linux |
As mentioned above, you might consider applying any appropriate or optional patches to the kernel's MASQ code BEFORE you compile the final kernel. The IP MASQ code found in the stock kernels is already very useful and does not require any specific patching in order for the system to work for NAT-friendly network applications. Many of these patches are only to fix possible known bugs, add new features (some are /very/ cool), etc. Please refer to Section 2.6 for URLs and the IP Masquerade Resources for up-to-date information and patch URLs.
Applying IPTABLES and Patch-o-Matic kernel patches
Download the iptables package and optional Patch-O-matics from the Section 2.6 and put it into a directory, say "/usr/src/archive/netfilter". Next, go into this new netfilter directory and uncompress the iptables archive with the command:
tar xyvf iptables-x.y.z.tar.bz2 tar xyvf patch-o-matic-x.tar.bz2 |
Now, go into the new iptables-x.y.x directory (/usr/src/archive/netfilter/iptables-x.y.z) and run the command
#For iptables v1.2.7a: make KERNEL_DIR=/usr/src/kernel/linux #For iptables v1.2.4 (when Patch-o-matic was built-in): make pending-patches KERNEL_DIR=/usr/src/kernel/linux |
NOTE: this assumes that your 2.4.x kernel sources are in the /usr/src/kernel/linux directory.
NOTE #2: If you append a "/" to the end of the above command line, you will get an error stating:
"make: *** [/usr/src/kernel/linux/include/asm/socket.h] Error 1". |
Here is an example of compiling IPTABLES v1.2.7a. Your output might look different depending on what version you are trying to use.
# make KERNEL_DIR=/usr/src/kernel/linux Extensions found: cc -O2 -Wall -Wunused -I/usr/src/kernel/linux/include -Iinclude/ -DIPTABLES_VERSION=\"1.2.7a\" -fPIC -o extensions/libipt_ah_sh.o -c extensions/libipt_ah.c ld -shared -o extensions/libipt_ah.so extensions/libipt_ah_sh.o cc -O2 -Wall -Wunused -I/usr/src/kernel/linux/include -Iinclude/ -DIPTABLES_VERSION=\"1.2.7a\" -fPIC -o extensions/libipt_conntrack_sh.o -c extensions/libipt_conntrack.c ld -shared -o extensions/libipt_conntrack.so extensions/libipt_conntrack_sh.o cc -O2 -Wall -Wunused -I/usr/src/kernel/linux/include -Iinclude/ -DIPTABLES_VERSION=\"1.2.7a\" -fPIC -o extensions/libipt_dscp_sh.o -c extensions/libipt_dscp.c extensions/libipt_dscp_helper.c:69: warning: `dscp_to_name' defined but not used ld -shared -o extensions/libipt_dscp.so extensions/libipt_dscp_sh.o . . . cc -O2 -Wall -Wunused -I/usr/src/kernel/linux/include -Iinclude/ -DIPTABLES_VERSION=\"1.2.7a\" -c -o libipulog/libipulog.o libipulog/libipulog.c ar rv libipulog/libipulog.a libipulog/libipulog.o a - libipulog/libipulog.o rm libiptc/libip6tc.o libiptc/libip4tc.o libipulog/libipulog.o libipq/libipq.o |
Ok, hopefully the IPTABLES program compiled up for you. Now, you need to install it. To do this, directory and run the command
make install KERNEL_DIR=/usr/src/kernel/linux |
Here is an example of installing IPTABLES v1.2.7a. Your output might look different depending on what version you are trying to use.
# make install KERNEL_DIR=/usr/src/kernel/linux cp iptables /usr/local/sbin/iptables cp iptables-save /usr/local/sbin/iptables-save cp iptables-restore /usr/local/sbin/iptables-restore cp ip6tables /usr/local/sbin/ip6tables cp extensions/libipt_ah.so /usr/local/lib/iptables/libipt_ah.so cp extensions/libipt_conntrack.so /usr/local/lib/iptables/libipt_conntrack.so cp extensions/libipt_dscp.so /usr/local/lib/iptables/libipt_dscp.so cp extensions/libipt_ecn.so /usr/local/lib/iptables/libipt_ecn.so cp extensions/libipt_esp.so /usr/local/lib/iptables/libipt_esp.so cp extensions/libipt_helper.so /usr/local/lib/iptables/libipt_helper.so . . . cp extensions/libip6t_udp.so /usr/local/lib/iptables/libip6t_udp.so cp extensions/libip6t_LOG.so /usr/local/lib/iptables/libip6t_LOG.so cp extensions/libip6t_MARK.so /usr/local/lib/iptables/libip6t_MARK.so |
Next, if you are interested in applying a Patch-O-Matic patch set, go into the patch-o-matic-X directory (/usr/src/archive/netfilter/patch-o-matic-X) and run the command
#For Patch-O-Matic later than the release of iptables v1.2.7a: KERNEL_DIR=/usr/src/kernel/linux ./runme pending |
NOTE #1: The use of the "pending" batch is the most common for IPMASQ functionality but there are several others. See below.
NOTE #2: this assumes that your 2.4.x kernel sources are in the /usr/src/kernel/linux directory.
NOTE #3: If you append a "/" to the end of the command line, you will get an error stating:
"make: *** [/usr/src/kernel/linux/include/asm/socket.h] Error 1". Remove the trailing "/" and try again. |
Here is an example of the Patch-O-Matic prompts you might receive for a 2.4.20 kernel with the "20030107" Patch-O-Matic set. You can also run the "runme" program in a batch mode to speed things up, add experimental patches, etc. if you'd like. To better understand your options, simply run the "./runme" command by itself. Please note that these prompts WILL CHANGE over time.
Welcome to Rusty's Patch-o-matic!
Each patch is a new feature: many have minimal impact, some do not.
Almost every one has bugs, so I don't recommend applying them all!
-------------------------------------------------------
Already applied: submitted/01_2.4.19
submitted/02_2.4.20
submitted/ipt_ULOG-mac_len-fix
submitted/ipt_multiport-invfix
pending/01_ip_conntrack_proto_tcp-lockfix
pending/02_newnat-udp-helper
pending/03_REJECT-fwspotting-phrack60-fix
pending/04_ftp-conntrack-msg-fix
Testing... 05_ECN-tcpchecksum-littleendian-fix.patch NOT APPLIED (1 rejects out
of 1 hunks)
The pending/05_ECN-tcpchecksum-littleendian-fix patch:
Author: Patrick McHardy
Status: Pending for kernel inclusion
The 2.4.20 kernel included the new iptables 'ECN' target, enabling a
selective
ECN disable mechanism. Unfortunately there was a bug in the incremental
TCP
checksum update, resulting in broken TCP checksums on little endian
machines.
This patch fixes the Bug.
Testing patch pending/05_ECN-tcpchecksum-littleendian-fix.patch...
Patch pending/05_ECN-tcpchecksum-littleendian-fix.patch applied cleanly.
Applying patch pending/05_ECN-tcpchecksum-littleendian-fix.patch...
Patch pending/05_ECN-tcpchecksum-littleendian-fix.patch applied cleanly.
Excellent! Kernel is now ready for compilation. |
If everything patches fine, you should see something like the text
Excellent! Kernel is now ready for compilation. |
towards the bottom of the screen. Beyond that, you don't have to install anything at this point. The next step is to compile the new PATCHED kernel.
Ok, now the new kernel is ready to be compiled but you should make sure that you also have the proper matching iptables program on your machine too (just to make sure). Run the command:
whereis iptables |
Now that the kernel sources are patched up, you need to configure it to know what kinds of features you need (HD support, Networking support, MASQ support, etc.). Here are the MINIMUM kernel configuration options required to enable IP Masquerade functionality. Please understand that this HOWTO illustrates just ONE way to configure and compile a kernel (modules vs static). The main difference from this example vs. an example given by a different MASQ guide is that some people might wish to compile kernel components either as modules OR monolithically into the kernel. Basically, compiling things as modules gives you added flexibility to what is or isn't installed into the kernel (reduces unneeded memory use for things you aren't / won't use and modules also allow for drop-in software upgrades [usually no need to reboot the machine]). On the flip side, kernel modules add more complexity to your configuration and sometimes the kernel auto-loader might make mistakes (not that I've ever seen this happen). Compiling things directly into the kernel makes things simpler BUT you loose a huge level of flexibility. The following kernel configuration example is a mixture of both a selection of kernel modules and building them in monolithically (you probably will ALWAYS need MASQ functionality ready to go).
Side Note: It is assumed that you will also configure the kernel to use your other installed hardware such as USB printers, Ethernet network interfaces, SCSI and IDE HD controllers, etc. as well. Please refer to the Linux Kernel HOWTO and the kernel source's "README" file and "Documentation/" directory for detailed help on compiling a kernel.
You will need to answer either YES, NO, or MODULE to the following program. Not all options will be available without the proper kernel patches described later in this HOWTO. This shouldn't be an issue as most 3rd party patches are only needed for a very select group of users.
Run the following commands to configure your kernel:
cd /usr/src/kernel/linux
make menuconfig
Please note the following kernel prompts reflect a 2.4.14 kernel (with some of the optional Patch-O-Matic additions. Please read the following carefully for recommendations:
[ Code maturity level options ]
* Prompt for development and/or incomplete code/drivers (CONFIG_EXPERIMENTAL) [Y/n/?]
- YES: though not required for IP MASQ, this option allows the kernel to create
the MASQ modules and enable the option for port forwarding
* Enable loadable module support (CONFIG_MODULES) [Y/n/?]
- YES: allows you to load kernel IP MASQ modules
* Set version information on all module symbols (CONFIG_MODVERSIONS) [Y/n/?]
- YES: allows newer kernels to load older modules if possible
* Kernel module loader (CONFIG_KMOD) [Y/n/?]
- OPTIONAL: Recommended : allows the kernel to load various kernel modules as it needs them
== Non-MASQ options skipped
== (CPU type, memory, SMP, FPU, specific stuff)
[ General setup ]
* Networking support (CONFIG_NET) [Y/n/?]
- YES: Enables the network subsystem
== Non-MASQ options skipped
== (specific hardware, PCI, kernel binaries, PCMCIA, etc.)
* Sysctl support (CONFIG_SYSCTL) [Y/n/?]
- YES: Enables the ability to enable disable options such as forwarding,
dynamic IPs, etc. via the /proc interface
[ Block devices ]
== Non-MASQ options skipped
== (kernel binaries, power management, PnP, RAID, etc.)
== Don't forget to compile in support for hardware that you might need:
== IDE controllers, HDs, CDROMs, etc.
[ Networking options ]
* Packet socket (CONFIG_PACKET) [Y/m/n/?]
- YES: Though this is OPTIONAL, this recommended feature will allow you
to use TCPDUMP to debug any problems with IP MASQ
* Packet socket: mmapped IO (CONFIG_PACKET_MMAP) [N/y/?] y
- YES: Speed up the packet protocol
* Kernel/User netlink socket (CONFIG_NETLINK) [Y/n/?]
- OPTIONAL: Recommended : this feature will allow the logging of
advanced firewall issues such as routing messages, etc
* Routing messages (CONFIG_RTNETLINK) [N/y/?] (NEW) y
- OPTIONAL: Allows for support of advanced kernel routing messages
if you enabled the CONFIG_NETLINK option
* Netlink device emulation (CONFIG_NETLINK_DEV) [N/y/m/?] (NEW)
- NO: This option does not have anything to do with packet firewall
logging
* Network packet filtering (replaces ipchains) (CONFIG_NETFILTER) [N/y/?] y
- YES: Enable this option to let IPTABLES configure the TCP/IP subsection
of the kernel. By enabling this, then you can turn on advanced
routing mechanisms like IP Masq, packet filtering, etc.
* Network packet filtering debugging (CONFIG_NETFILTER_DEBUG) [N/y/?] (NEW) n
- NO: Not required for Masquerading functionality though it may help
for troubleshooting. There might be a performance penalty when
enabling this.
* Socket Filtering (CONFIG_FILTER) [Y/n/?]
- OPTIONAL: Recommended : Though this doesn't have anything do with IPMASQ,
if you plan on implimenting a DHCP server on the internal network, you WILL
need to enable this option.
* Unix domain sockets (CONFIG_UNIX) [Y/m/n/?]
- YES: This enables the UNIX TCP/IP sockets mechanisms
* TCP/IP networking (CONFIG_INET) [Y/n/?]
- YES: Enables the TCP/IP protocol
* IP: multicasting (CONFIG_IP_MULTICAST) [N/y/?]
- OPTIONAL: You can enable this if you want to be able to receive
Multicast traffic. Please note that your ISP must
support Multicast as well for this all to work at all
* IP: advanced router (CONFIG_IP_ADVANCED_ROUTER) [Y/n/?]
- OPTIONAL: Though there is nothing in this section mandatory for
Masquerade, some specific options might be useful
== Non-MASQ options skipped
== ( autoconf, tunneling )
* IP: multicast routing (CONFIG_IP_MROUTE) [N/y/?] n
- OPTIONAL: Though not needed for IPMASQ, enabling this feature will
let you route multicast traffic through your Linux box.
Please note that this requires that your ISP be multicast
enabled as well.
== Non-MASQ options skipped
== (ARPd)
* IP: TCP Explicit Congestion Notification support (CONFIG_INET_ECN) [N/y/?] n
- NO: Though enabling this option would be great, there are many Internet
sites out there that will block this. Hit the "?" when configuring
the kernel to learn more about it but it is recommended to say NO for
now.
* IP: TCP syncookie support (disabled per default) (CONFIG_SYN_COOKIES) [Y/n/?]
- YES: Recommended : for basic TCP/IP network security
[ Networking options --> IP: Netfilter Configuration ]
* Connection tracking (required for masq/NAT) (CONFIG_IP_NF_CONNTRACK) [N/y/m/?] (NEW) m
- YES: (Module) This enables the kernel to track various network connections.
This option is required for Masquerading support as well as to enable
Stateful tracking for various filewall mechanisms. Please note that
if you compile this directly into the kernel, you cannot enable
the legacy IPCHAINS or IPFWADM compatibility modules.
* FTP protocol support (CONFIG_IP_NF_FTP) [M/n/?] (NEW) m
- YES: (Module) This enables the proper Masquerading of FTP connections if
CONFIG_IP_NF_CONNTRACK was enabled above
* IRC protocol support (CONFIG_IP_NF_IRC) [M/n/?] (NEW) m
- YES: (Module) This enables the proper Masquerading of IRC connections if
CONFIG_IP_NF_CONNTRACK was enabled above
* Userspace queueing via NETLINK (EXPERIMENTAL) (CONFIG_IP_NF_QUEUE) [N/y/m/?] (NEW) m
- OPTIONAL: Though this is OPTIONAL, this feature will allow IPTABLES to
copy specific packets to UserSpace tools for additional checks
* IP tables support (required for filtering/masq/NAT) (CONFIG_IP_NF_IPTABLES) [N/y/m/?] (NEW) m
- YES: (Module) Enables IPTABLES support
* limit match support (CONFIG_IP_NF_MATCH_LIMIT) [N/y/m/?] (NEW) y
- OPTIONAL: (Module) Recommended : Though not required, this option can used to
enable rate limiting of both traffic and loggin messages help slow down denial
of service (DoS) attacks.
* MAC address match support (CONFIG_IP_NF_MATCH_MAC) [N/y/m/?] (NEW) m
- OPTIONAL: Though not required, the option can allow you to
filter traffic based upon the SOURCE Ethernet MAC address.
* netfilter MARK match support (CONFIG_IP_NF_MATCH_MARK) [N/y/m/?] (NEW) y
- YES: (Module) Recommended : This enables IPTABLES to take action upon marked packets.
This mechanism can allow for PORTFW functionality, TOS marking, etc.
* Multiple port match support (CONFIG_IP_NF_MATCH_MULTIPORT) [N/y/m/?] (NEW) y
- YES: (Module) Recommended : This enables IPTABLES to accept mutliple SRC/DST port
ranges (non-contiguous) instead of one port range per IPTABLES
statement.
* TOS match support (CONFIG_IP_NF_MATCH_TOS) [Y/m/n/?] n
- OPTIONAL: This allows IPTABLES to match packets based upon their
DIFFSERV settings.
* LENGTH match support (CONFIG_IP_NF_MATCH_LENGTH) [N/m/?] (NEW) n
- OPTIONAL: This allows IPTABLES to match packets based upon their
packet length.
* TTL match support (CONFIG_IP_NF_MATCH_TTL) [N/m/?] (NEW) ? n
- OPTIONAL: This allows IPTABLES to match packets based upon their
TTL settings.
* tcpmss match support (CONFIG_IP_NF_MATCH_TCPMSS) [N/y/m/?] m
- OPTIONAL: (Module) Recommended : This option allows users to examine the MSS value in
TCP SYN packets. This is an advanced knob but can be very valuable in
troubleshooting MTU problems.
* Connection state match support (CONFIG_IP_NF_MATCH_STATE) [M/n/?] m
- YES: (Module) Recommended : This option allows for Stateful tracking of network
connections.
* Unclean match support (EXPERIMENTAL) (CONFIG_IP_NF_MATCH_UNCLEAN) [N/y/m/?] y
- YES: (Module) Recommended : This option allows for connection tracking on odd packets.
It cal also help in the detection of possibly malicious packets.
This can be a valuable tool in tracking hostile people on the network.
* Owner match support (EXPERIMENTAL) (CONFIG_IP_NF_MATCH_OWNER) [N/y/m/?] n
- OPTIONAL: This option allows IPTABLES to match traffic based upon the
user login, group, etc. who created the traffic.
* Packet filtering (CONFIG_IP_NF_FILTER) [N/y/m/?] ? y
- YES: (Module) This option allows for the kernel to be able filter traffic at
the INPUT, FORWARDING, and OUTPUT traffic points.
* REJECT target support (CONFIG_IP_NF_TARGET_REJECT) [N/y/m/?] (NEW) y
- YES: (Module) With this option, a packet firewall can send an ICMP Reject packet
back to the originator when a packet is blocked.
* MIRROR target support (EXPERIMENTAL) (CONFIG_IP_NF_TARGET_MIRROR) [N/y/m/?] (NEW) n
- OPTIONAL: This option allows the packet firewall to mirror the exact same
network packet back to the originator when it is supposed to be
blocked. This is similar to the REJECT option above but it actually
sends the original packet back to the originator. i.e. a
hostile user could actually portscan themselves.
* Full NAT (CONFIG_IP_NF_NAT) [M/n/?] m
- YES: (Module) This option enables the future menus to enable Masquerading,
PORTFWing, Full (1:1) NAT, etc.
* MASQUERADE target support (CONFIG_IP_NF_TARGET_MASQUERADE) [M/n/?] (NEW) m
- YES: (Module) This option specifically enables Masquerade into the
kernel
* REDIRECT target support (CONFIG_IP_NF_TARGET_REDIRECT) [N/y/m/?] n
- OPTIONAL: Not needed for normal MASQ functionality though people who
want to do transparent proxy via Squid will want this.
* Basic SNMP-ALG support (EXPERIMENTAL) (CONFIG_IP_NF_NAT_SNMP_BASIC) [N/m/?] n
- OPTIONAL: This enables IPTABLES to properly NAT internal SNMP packets so
that machines with duplicate addressing ranges can be properly
managed.
* Packet mangling (CONFIG_IP_NF_MANGLE) [N/y/m/?] y
- YES: (Module) This option allows for advanced IPTABLES packet manipulation
options.
* TOS target support (CONFIG_IP_NF_TARGET_TOS) [N/y/m/?] (NEW) n
- OPTIONAL: Enables the kernel to modify the TOS field in a packet
before routing it on
* MARK target support (CONFIG_IP_NF_TARGET_MARK) [N/y/m/?] (NEW) m
- OPTIONAL: (Module) Recommended : This enables the kernel to manipulate
packets based upon the MARK field. This can be used for PORTFW
as well as many other things.
* LOG target support (CONFIG_IP_NF_TARGET_LOG) [N/y/m/?] m
- YES: (Module) This allows for the logging of packets before they are accepted,
denied, rejected, etc.
* TCPMSS target support (CONFIG_IP_NF_TARGET_TCPMSS) [N/y/m/?] ? m
- YES: (Module) This option help some people with MTU problems. Typically,
most users have to set their Internet connection's MTU to
1500 as well as ALL internal machines to 1500. With this
option, this whole MTU issue might be finally solved.
* ipchains (2.2-style) support (CONFIG_IP_NF_COMPAT_IPCHAINS) [N/y/m/?] m
- OPTIONAL: (Module) Recommended : If you have an existing IPCHAINS ruleset
(2.2.x kernels) and enable this option, you can continue to use the
IPCHAINS program and the majority of your old ruleset except for the
use of any 2.2.x kernel-specific modules. Please note that if this
IPCHAINS module is loaded, ALL IPTABLES modules will be non-
operational. This is an either/or deal only intended for legacy
rulesets.
* ipfwadm (2.0-style) support (CONFIG_IP_NF_COMPAT_IPFWADM) [N/y/m/?] n
- OPTIONAL: If you have an existing IPFWADM ruleset (2.0.x kernels) and
enable this option, you can continue to use the IPFWADM program and
the majority of your old ruleset except for the use of any 2.0.x
kernel-specific modules. Please note that if this IPFWADM module
is loaded, ALL IPTABLES modules will be non operational. This is
an either/or deal only intended to support legacy rulesets.
== Non-MASQ options skipped
== (IPv6, khttpd, ATM, IPX, AppleTalk, etc.) --
* Fast switching (read help!) (CONFIG_NET_FASTROUTE) [N/y/?] n
- NO: This performance optimization is NOT compatible with IP MASQ and/or
packet filtering
== Non-MASQ options skipped
== (QoS, Telephony, IDE, SCSI, 1394FW, I2O, etc)
== Don't forget to compile in support for hardware that you might need:
== IDE: HDs, CDROMs, etc.
== SCSI: HDs, CDROMs, etc.
[ Network device support ]
* Network device support (CONFIG_NETDEVICES) [Y/n/?]
- YES: Enables the Linux Network device sublayer
== Non-MASQ options skipped
== (Arcnet)
* Dummy net driver support (CONFIG_DUMMY) [M/n/y/?]
- YES: Though OPTIONAL, this option can help when debugging problems
== Non-MASQ options skipped
== (EQL, etc..)
== Don't forget to compile in support for hardware that you might need:
== NICs: eth, tr, etc.
== MODEMs: ppp (ppp async) and/or slip
== WANs: T1, T3, ISDN, etc.
== ISDN: for internal ISDN modems
== Non-MASQ options skipped
== (Amateur Radio, IrDA, ISDN, USB, etc.)
[ Character devices ]
== Don't forget to compile in serial port support if you are a modem user
== Don't forget to compile in mouse support
== Non-MASQ options skipped
== (I2C, Watchdog cards, Ftape, Video for Linux, etc. )
[ File systems ]
== Non-MASQ options skipped
== (Quota, ISO9660, NTFS, etc )
* /proc filesystem support (CONFIG_PROC_FS) [Y/n/?]
- YES: Required to dynamically configure the Linux forwarding
and NATing systems
== Non-MASQ options skipped
== (Console drivers, Sound, USB, Kernel Hacking)
|
NOTE: These are just the kernel components you need for IP Masquerade networking support. You will need to select whatever other options needed for your specific setup. If you want more information on what each one of these kernel modules does, please see the FAQ section of this HOWTO for details.
Now compile the kernel (make dep; make clean; make bzImage; make modules; make modules_install) , etc. Again, it is beyond the scope of this HOWTO if you have problems compiling your kernel. Please see Section 2.6 for URLs to the KERNEL howto, etc.
You will then have move over the kernel binary, update your bootloader (LILO, Grub, etc.), and reboot. If you have questions about kernel compiling, I highly recommend to consult some of the URLs mentioned above in this section.
Please see Section 2.7 for any required software, patches, etc.
First of all, you need the kernel source for 2.2.x (preferably the latest kernel version)
NOTE #1: --- UPDATE YOUR KERNEL --- Linux 2.2.x kernels less than version 2.2.20 contain several different security vulnerabilities (some were MASQ specific). Kernels less than 2.2.20 have a few local vulnerabilities. Kernel versions less than 2.2.16 have a TCP root exploit vulnerability and versions less than 2.2.11 have a IPCHAINS fragmentation bug. Because of these issues, users running a firewall with strong IPCHAINS rulesets are open to possible instrusion. Please upgrade your kernel to a fixed version.
NOTE #2: As the 2.2.x train progressed, the compile-time options keep on changing. As of this version, this section reflects the settings for a 2.2.20 kernel.
If you are running either a newer or older kernel version, the dialogs will look different. It is recommended that you update to the newest kernel for added capability and stability of the system.
If this is your first time compiling the kernel, don't be scared. In fact, it's rather easy and it's covered in several URLs found in Section 2.7. Please note that the instructions included here is just one way to do build a kernel. Please see the Kernel HOWTO for full details.
NOTE: Please notice that it isn't recommended to put the new kernel sources into /usr/src/linux. You should leave the original kernel sources that came with your Linux distribution in /usr/src/linux. For more details on this topic, please read the "README" file in the top level directory of your kernel sources.
For this HOWTO example, create a directory called /usr/src/kernel. Next, "cd" into this directory and download the newest 2.2.x kernel sources into it. Once downloaded, issue the following command (if the file ends in a .tar.gz): tar xvzf linux-2.2.x.tar.gz or (if the file ends in a .tar.bzip2): tar xyvf linux-2.2.x.tar.bz2. Please substitute the "x" in the 2.2.x filename with the Linux 2.2 kernel version you downloaded.
NOTE: Some Linux distributions use the "I" option instead of the "y" option to decompress bzip2 archives.
Once uncompressed, I recommend that you rename the directory from "linux" to "linux-2.2.x" for clarity. To do this, run the command mv linux linux-2.2.x. Next, make sure there is a directory or symbolic link pointing to /usr/src/kernel/linux ie. run the command: ln -s /usr/src/kernel/linux-2.2.x /usr/src/kernel/linuxo again subsituting the "x" for your proper kernel version.
Apply any appropriate or optional patches to the kernel source code. By default, stock Linux kernels do not require any specific patching in order for the system to work. Features like PPTP/IPSEC masqurading are already built-in in the newest kernels but other tools like Xwindows forwarders are optional. Please refer to Section 2.7 for URLs and the IP Masquerade Resources for up-to-date information and patch URLs.
Now that the kernel is patched up (if required), here are the MINIMUM kernel configuration options required to enable IP Masquerade functionality. Please understand that this HOWTO illustrates just ONE way to compile a kernel. The main difference from this method vs. a different one is some people wish to compile things either as modules OR monolithically right into the kernel. Basically, compiling things as modules gives you added flexibility to what is or isn't installed into the kernel (reduces unneeded memory use and allow for drop-in upgrades [no need to reboot]) BUT they add more complexity to your configuration. On the flip side, compiling things directly into the kernel makes things simpler BUT you loose a level of flexibility. The following example is a mixture of both built-in AND modules.
Side Note: It is assumed that you will also configure the kernel to use your other installed hardware such as network interfaces, optional SCSI controllers, etc. as well. Please refer to the Linux Kernel HOWTO and the kernel source's README file and Documentation/ directory for detailed help on compiling a kernel.
Please note the YES or NO ANSWERS to the following. Not all options will be available without the proper kernel patches described later in this HOWTO.
Run the following commands to configure your kernel:
cd /usr/src/kernel/linux
make menuconfig
The following kernel prompts reflect a 2.2.20 kernel:
[ Code maturity level options ]
* Prompt for development and/or incomplete code/drivers (CONFIG_EXPERIMENTAL) [Y/n/?]
- YES: though not entirely required for IP MASQ, this option allows the kernel
to create possible additional MASQ modules such as PORTFW, etc.
== Non-MASQ options skipped
== (CPU, memory, MTRR, SMP, etc.)
[ Loadable module support ]
* Enable loadable module support (CONFIG_MODULES) [Y/n/?] y
- YES: allows you to load kernel IP MASQ modules
* Set version information on all symbols for modules (CONFIG_MODVERSIONS) [N/y/?] y
- YES: allows newer kernels to load older modules if possible
* Kernel module loader (CONFIG_KMOD) [Y/n/?] y
- OPTIONAL: Recommended : allows the kernel to load various kernel modules as
it needs them
[ General setup ]
* Networking support (CONFIG_NET) [Y/n/?]
- YES: This enables the network subsystem
== Non-MASQ options skipped
== (PCI, kernel binaries, specific hardware options, etc.)
* Sysctl support (CONFIG_SYSCTL) [Y/n/?]
- YES: Enables the ability to enable disable options such as forwarding,
dynamic IPs, etc. via the /proc interface
[ Block devices ]
== Non-MASQ options skipped
== (kernel binaries, power management, PnP, IDE, SCSI, etc.)
== Don't forget to compile in support for hardware that you might need:
== IDE controllers, HDs, CDROMs, etc.
[ Networking options ]
* Packet socket (CONFIG_PACKET) [Y/m/n/?] y
- YES: Though this is OPTIONAL, this recommended feature will allow you
to use TCPDUMP to debug any problems with IP MASQ
* Kernel/User netlink socket (CONFIG_NETLINK) [Y/n/?] y
- OPTIONAL: Recommended : This feature will allow the logging of
advanced firewall issues such as routing messages, etc
* Routing messages (CONFIG_RTNETLINK) [Y/n/?] y
- OPTIONAL: If you enabled the CONFIG_NETLINK option above, this option
will send routing messages and other information to SYSLOG.
* Netlink device emulation (CONFIG_NETLINK_DEV) [N/y/m/?] (NEW) n
- NO: This option does not have anything to do with packet firewall
logging
* Network firewalls (CONFIG_FIREWALL) [Y/n/?] y
- YES: Enables the kernel to be comfigured by the IPCHAINS firewall tool
* Socket Filtering (CONFIG_FILTER) [Y/n/?] y
- OPTIONAL: Though this doesn't have anything do with IPMASQ, if you
plan on implimenting a DHCP server on the internal network, you
WILL need this option.
* Unix domain sockets (CONFIG_UNIX) [Y/m/n/?] y
- YES: This enables the UNIX TCP/IP sockets mechanisms
* TCP/IP networking (CONFIG_INET) [Y/n/?] y
- YES: Enables the TCP/IP protocol
* IP: multicasting (CONFIG_IP_MULTICAST) [N/y/?] y
- OPTIONAL: You can enable this if you want to be able to receive
Multicast traffic. Please note that your ISP must
support Multicast as well for this all to work
* IP: advanced router (CONFIG_IP_ADVANCED_ROUTER) [Y/n/?] n
- OPTIONAL: Though there is nothing in this section mandatory for
Masquerade, some specific options might be useful
* IP: kernel level autoconfiguration (CONFIG_IP_PNP) [N/y/?] ?
- NO: Not needed for normal MASQ functionality
* IP: firewalling (CONFIG_IP_FIREWALL) [Y/n/?] y
- YES: This enables the kernel to support packet filtering, NAT, etc.
* IP: firewall packet netlink device (CONFIG_IP_FIREWALL_NETLINK) [Y/n/?] n
- OPTIONAL: Though this is OPTIONAL, this feature will allow IPCHAINS to
copy some packets to UserSpace tools for additional checks
* IP: transparent proxy support (CONFIG_IP_TRANSPARENT_PROXY) [N/y/?] n
- OPTIONAL: Not needed for normal MASQ functionality though people who
want to do transparent proxy via Squid will want this. Please note
that there is a PERFORMANCE PENALTY enabling this feature.
* IP: masquerading (CONFIG_IP_MASQUERADE) [Y/n/?] y
- YES: Enable IP Masquerade to re-address specific internal to external
TCP/IP packets
* IP: ICMP masquerading (CONFIG_IP_MASQUERADE_ICMP) [Y/n/?] y
- YES: Enable support for masquerading ICMP ping packets (ICMP error
codes will be MASQed regardless). This is an important feature
for troubleshooting connections.
* IP: masquerading special modules support (CONFIG_IP_MASQUERADE_MOD) [Y/n/?] y
- YES: Though OPTIONAL, this enables the option to later enable other
modules like the PORTFW to give external computers a directly
connection to specified internal MASQed machines.
* IP: ipautofw masq support (EXPERIMENTAL) (CONFIG_IP_MASQUERADE_IPAUTOFW) [N/y/m/?] n
- NO: NOT recommended : IPautofw is a legacy method of port forwarding. It
is mainly old code and has been found to have some issues.
* IP: ipportfw masq support (EXPERIMENTAL) (CONFIG_IP_MASQUERADE_IPPORTFW) [Y/m/n/?] y
- OPTIONAL: Recommended : This enables PORTFW which allows external computers
on the Internet to directly communicate to specified internal MASQed
machines. This feature is typically used to allow access to internal
SMTP, TELNET, and WWW servers. Please note that FTP port forwarding
needs an additional patch, as described in the FAQ section of the MASQ
HOWTO. Please see the this FAQ section in the HOWTO for additional
information.
* IP: ip fwmark masq-forwarding support (EXPERIMENTAL) (CONFIG_IP_MASQUERADE_MFW) [Y/m/n/?] y
- OPTIONAL: This is a NEW method of performing PORTFW-like functionality which is
similar to how the new 2.4.x kernels do things. With this option, IPCHAINS
can mark packets that should have additional work done upon it. Using a
UserSpace tool, much like IPMASQADM or IPPORFW, IPCHAINS would then
do things like re-address the packets, change their TOS value, etc.
Currently, this code is less tested than PORTFW but it looks promising.
For now, this HOWTO recommends to use IPMASQADM and IPPORTFW. If you
have specific thoughts or comments on MFW, please email dranch.
* IP: optimize as a router not host (CONFIG_IP_ROUTER) [Y/n/?] y
- YES: This optimizes the kernel for the network subsystem, though it
isn't well known if this makes a siginificant performance difference
or not.
== Non-MASQ options skipped
== ( autoconf, tunneling, GRE )
* IP: multicast routing (CONFIG_IP_MROUTE) [N/y/?] n
- OPTIONAL: Though not needed for IPMASQ, enabling this feature will
let you route multicast traffic through your Linux box.
Please note that this requires that your ISP be multicast
enabled as well.
== Non-MASQ options skipped
== (Aliasing, ARPd)
* IP: TCP syncookie support (disabled per default) (CONFIG_SYN_COOKIES) [Y/n/?]
- YES: Recommended : for basic TCP/IP network security
* IP: GRE tunnels over IP (CONFIG_NET_IPGRE) [N/y/m/?]
- NO: This OPTIONAL selection is to enable PPTP and GRE tunnels through
the IP MASQ box
== Non-MASQ options skipped
== (aliasing, ARPd)
* IP: TCP syncookie support (not enabled per default) (CONFIG_SYN_COOKIES) [Y/n/?]
- YES: HIGHLY recommended for basic TCP/IP network security
== Non-MASQ options skipped
== (RARP)
* IP: Allow large windows (not recommended if <16Mb of memory) * (CONFIG_SKB_LARGE) [Y/n/?]
- YES: This is recommended to optimize Linux's TCP window
== Non-MASQ options skipped
== (IPv6, IPX, WAN router, etc.)
* Fast switching (read help!) (CONFIG_NET_FASTROUTE) [N/y/?] n
- NO: This performance optimization is NOT compatible with IP MASQ and/or
packet filtering
== Non-MASQ options skipped
== (Slow CPU, Telephony, SCSI, I2O, etc. )
== Don't forget to compile in support for hardware that you might need:
== SCSI: HDs, CDROMs, etc.
[ Network device support ]
* Network device support (CONFIG_NETDEVICES) [Y/n/?]
- YES: Enables the Linux Network device sublayer
== Non-MASQ options skipped
== (Arcnet)
* Dummy net driver support (CONFIG_DUMMY) [M/n/y/?]
- YES: Though OPTIONAL, this option can help when debugging problems
== Non-MASQ options skipped
== (EQL, NICs, Wireless, IrDA, ISDN, etc..)
== Don't forget to compile in support for hardware that you might need:
== NICs: eth, tr, etc.
== MODEMs: ppp and/or slip
== WANs: T1, T3, ISDN, etc.
== ISDN: for internal ISDN modems
[ Character devices ]
== Don't forget to compile in serial port support for modem users
== Don't forget to compile in mouse support
== Non-MASQ options skipped
== (I2C, Watchdog cards, Ftape, Video for Linux, USB, etc. )
[ File systems ]
== Non-MASQ options skipped
== (Quota, ISO9660, NTFS, etc )
* /proc filesystem support (CONFIG_PROC_FS) [Y/n/?]
- YES: Required to dynamically configure the Linux forwarding
and NATing systems
== Non-MASQ options skipped
== (network fs, NLS, video section, sound, kernel hacking) |
NOTE: These are just the components you need for IP Masquerade. You will need to select whatever other options needed for your specific setup.
Now compile the kernel (make dep; make clean; make bzImage; make modules; make modules_install) , etc. Again, it is beyond the scope of this HOWTO if you have problems compiling your kernel. Please see Section 2.7 for URLs to the KERNEL howto, etc.
You will then have move over the kernel binary, update your bootloader (LILO, Grub, etc.), and reboot. If you have questions about kernel compiling, I highly recommend to consult some of the URLs above in this section.
Please see Section 2.8 for any required software, patches, etc.
First of all, you need the kernel source for 2.0.x (preferably the latest kernel version)
As the 2.0.x train progress, the compile-time options keep on changing. As of this version, this section reflects the settings for a 2.0.39 kernel.
If this is your first time compiling the kernel, don't be scared. In fact, it's rather easy and it's covered in several URLs found in Section 2.8. Please note that the instructions included here is just one way to do build a kernel. Please see the Kernel HOWTO for full details.
NOTE: Please notice that it isn't recommended to put the new kernel sources into /usr/src/linux. You should leave the original kernel sources that came with your Linux distribution in /usr/src/linux. For more details on this topic, please read the "README" file in the top level directory of your kernel sources.
For this HOWTO example, create a directory called /usr/src/kernel. Next, "cd" into this directory and download the newest 2.0.x kernel sources into it. Once downloaded, issue the following command: tar xvzf linux-2.0.x.tar.gz . Please substitute the "x" in the 2.0.x filename with the Linux 2.0 kernel version you downloaded.
Once uncompressed, I recommend that you rename the directory from "linux" to "linux-2.0.x" for clarity. To do this, run the command mv linux linux-2.0.x. Next, make sure there is a directory or symbolic link pointing to /usr/src/kernel/linux ie. run the command: ln -s /usr/src/kernel/linux-2.0.x /usr/src/kernel/linuxo again subsituting the "x" for your proper kernel version.
Apply any appropriate or optional patches to the kernel source code. By default, stock Linux kernels do not require any specific patching in order for the system to work. Features like IPPORTFW, PPTP, and Xwindows forwarders are optional but very useful. Please refer to Section 2.8 for URLs and the IP Masquerade Resources for up-to-date information and patch URLs.
Now that the kernel is patched up (if required), here are the MINIMUM kernel configuration options required to enable IP Masquerade functionality. Please understand that this HOWTO illustrates just ONE way to compile a kernel. The main difference from this method vs. a different one is some people wish to compile things either as modules OR monolithically right into the kernel. Basically, compiling things as modules gives you added flexibility to what is or isn't installed into the kernel (reduces unneeded memory use and allow for drop-in upgrades [no need to reboot]) BUT they add more complexity to your configuration. On the flip side, compiling things directly into the kernel makes things simpler BUT you loose a level of flexibility. The following example is a mixture of both built-in AND modules.
Side Note: It is assumed that you will also configure the kernel to use your other installed hardware such as network interfaces, optional SCSI controllers, etc. as well. Please refer to the Linux Kernel HOWTO and the kernel source's "README" file and "Documentation/" directory for detailed help on compiling a kernel.
Please note the YES or NO ANSWERS to the following options. Not all options will be available without the proper kernel patches described later in this HOWTO:
Run the following commands to configure your kernel:
cd /usr/src/kernel/linux
make menuconfig
The following kernel prompts reflect a 2.0.39 kernel:
[ Code maturity level options ]
* Prompt for development and/or incomplete code/drivers (CONFIG_EXPERIMENTAL) [Y/n/?]
- YES: this will allow you to later select the IP Masquerade feature code
[ Loadable module support ]
* Enable loadable module support (CONFIG_MODULES) [Y/n/?] y
- YES: allows you to load kernel IP MASQ modules
* Set version information on all module symbols (CONFIG_MODVERSIONS) [N/y/?] y
- YES: allows newer kernels to load older modules if possible
* Kernel daemon support (e.g. autoload of modules) (CONFIG_KERNELD) [N/y/?] y
- OPTIONAL: Recommended : allows the kernel to load various kernel modules as
it needs them
[ General setup ]
== Non-MASQ options skipped
== (FPU, memory)
* Networking support (CONFIG_NET) [Y/n/?] y
- YES: Enables the network subsystem
== Non-MASQ options skipped
== (memory, PCI, binary format, APM, etc.)
== Don't forget to compile in support for hardware that you might need:
== IDE controllers, HDs, CDROMs, etc.
[ Networking options ]
* Network firewalls (CONFIG_FIREWALL) [Y/n/?] y
- YES: Enables the IPFWADM firewall tool
== Non-MASQ options skipped
== (Aliasing)
* TCP/IP networking (CONFIG_INET) [Y/n/?] y
- YES: Enables the TCP/IP protocol
* IP: forwarding/gatewaying (CONFIG_IP_FORWARD) [N/y/?] y
- YES: Enables Linux network packet forwarding and routing
- Controlled by IPFWADM
* IP: multicasting (CONFIG_IP_MULTICAST) [N/y/?] y
- OPTIONAL: You can enable this if you want to be able to receive
Multicast traffic. Please note that your ISP must
support Multicast as well for this all to work
* IP: syn cookies (CONFIG_SYN_COOKIES) [Y/n/?] y
- YES: HIGHLY recommended for basic network security
* IP: firewalling (CONFIG_IP_FIREWALL) [Y/n/?] y
- YES: Enable the packet firewall features
* IP: firewall packet logging (CONFIG_IP_FIREWALL_VERBOSE) [Y/n/?] y
- YES: Allows the kernel to report back on various packets traversing
the firewall.
* IP: masquerading (CONFIG_IP_MASQUERADE [Y/n/?] y
- YES: Enable the kernel to perform IP MASQ NAT functionality
* IP: ipautofw masquerade support (EXPERIMENTAL) (CONFIG_IP_MASQUERADE_IPAUTOFW) [Y/n/?] n
- NO: NOT Recommended : IPautofw is a legacy method of TCP/IP port forwarding.
Though IPautofw works, IPPORTFW is a better choice.
* IP: ipportfw masq support (EXPERIMENTAL) (CONFIG_IP_MASQUERADE_IPPORTFW) [Y/n/?] y
- YES: This option is ONLY AVAILABLE VIA A PATCH for the 2.0.x kernels.
With this option, external computers on the Internet can directly
communicate to specified internal MASQed machines. This feature is
typically used to access internal SMTP, TELNET, and WWW servers.
FTP port forwarding sometimes might require an additional patch as
described in the FAQ section. Additional information on port
forwarding is available in the Forwards section of this HOWTO.
* IP: MS PPTP masq support (EXPERIMENTAL) (CONFIG_IP_MASQUERADE_PPTP) [N/y/?] (NEW) n
- OPTIONAL: Enabling this feature will allow internal MASQ clients to
properly connect to PPTP servers on the Internet.
* IP: MS PPTP Call ID masq support (CONFIG_IP_MASQUERADE_PPTP_MULTICLIENT) [N/y/?] (NEW) n
- OPTIONAL: If you enabled the CONFIG_IP_MASQUERADE_PPTP above, this
option will allow for multiple internal PPTP clients behind the MASQ
server to communicate to the same PPTP server.
* IP: MS PPTP masq debugging (DEBUG_IP_MASQUERADE_PPTP) [N/y/?] n
- OPTIONAL: NOT recommended : This is not required for IP MASQ or MASQing PPTP
connections unless you need additional troubleshooting help. If enabled,
this can fill up your logs quickly.
* IP: MS PPTP masq verbose debugging (DEBUG_IP_MASQUERADE_PPTP_VERBOSE) [N/y/?] (NEW) n
- OPTIONAL: NOT Recommended : If you enabled the DEBUG_IP_MASQUERADE_PPTP
option above, this will make the logging even more verbose.
* IP: IPSEC ESP & ISAKMP masq support (EXPERIMENTAL) * (CONFIG_IP_MASQUERADE_IPSEC) [N/y/?] m
- OPTIONAL: This option allows for some forms of IPSEC tunnels to be
masquraded
* IP: IPSEC masq table lifetime (minutes) (CONFIG_IP_MASQUERADE_IPSEC_EXPIRE) * [30] (NEW)
- OPTIONAL: This feature allows to change the MASQ table timeouts so that
idle IPSEC tunnels won't be prematurely disconnected.
* IP: Disable inbound ESP destination guessing * (CONFIG_IP_MASQUERADE_IPSEC_NOGUESS) [N/y/?] n
- OPTIONAL: This feature allows the kernel to guess where the fully encrypted IPSEC VPN
might be going and add it to the MASQ table.
* IP: IPSEC masq debugging (DEBUG_IP_MASQUERADE_IPSEC) [N/y/?] ? n
- OPTIONAL: NOT recommended : This is not required for IP MASQ or MASQing IPSEC
connections unless you need additional troubleshooting help. If enabled,
this can fill up your logs quickly.
* IP: IPSEC masq verbose debugging (DEBUG_IP_MASQUERADE_IPSEC_VERBOSE) [N/y/?] (NEW) n
- OPTIONAL: NOT Recommended : If you enabled the DEBUG_IP_MASQUERADE_IPSEC
option above, this will make the logging even more verbose.
* IP: ICMP masquerading (CONFIG_IP_MASQUERADE_ICMP) [Y/n/?]
- YES: Enable support for masquerading ICMP packets. Though thought of as
optional, many programs will NOT function properly with out ICMP
support.
* IP: transparent proxy support (EXPERIMENTAL) (CONFIG_IP_TRANSPARENT_PROXY) [N/y/?] n
- OPTIONAL: Not needed for normal MASQ functionality though people who
want to do transparent proxy via Squid will want this. Please note
that there is a PERFORMANCE PENALTY enabling this feature.
* IP: loose UDP port managing (EXPERIMENTAL) (CONFIG_IP_MASQ_LOOSE_UDP) [Y/n/?]
- YES: This option is ONLY AVAILABLE VIA A PATCH for the 2.0.x kernels.
With this option, internally masqueraded computers can play
NAT-friendly games over the Internet. Explicit details are given
in the FAQ section of this HOWTO.
* IP: always defragment (CONFIG_IP_ALWAYS_DEFRAG) [Y/n/?]
- YES: This feature optimizes IP MASQ connections
== Non-MASQ options skipped
== (Accounting)
* IP: optimize as router not host (CONFIG_IP_ROUTER) [Y/n/?]
- YES: This optimizes the kernel for the network subsystem
== Non-MASQ options skipped
== (Tunneling, Mcast routing, RARP, PMTU, etc.)
* IP: Drop source routed frames (CONFIG_IP_NOSR) [Y/n/?]
- YES: HIGHLY recommended for basic network security
== Non-MASQ options skipped
== (IPX, Bridging, SCSI, etc.)
== Don't forget to compile in support for hardware that you might need:
== SCSI controllers, HDs, CDROMs, etc.
[ Network device support ]
* Network device support (CONFIG_NETDEVICES) [Y/n/?]
- YES: Enables the Linux Network device sublayer
== Non-MASQ options skipped
== (Dummy, EQL, PPP, SLIP, NICs, Wireless, etc.)
== Don't forget to compile in support for hardware that you migh |