INTERVIEW QUESTIONS OPERATING SYSTEMS IP MASQUERADING DETAILS

Question: Requirements for IP Masquerade on Linux 2.4.x

Answer: ** 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 [http://www.netfilter.org/documentation/
pomlist/pom-summary.html] 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] 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] http://www.netfilter.org/
documentation/index.html#HOWTO and more specifically [http://
www.netfilter.org/documentation/HOWTO//NAT-HOWTO.html] 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/] 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/] 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 [http://
www.netfilter.org/] Unreliable IPTABLES HOWTOs page.


* Loadable kernel modules, preferably 2.1.121 or higher, are available from
[http://home.pi.se/blox/modutils/index.html] http://home.pi.se/blox/
modutils/index.html or [ftp://ftp.kernel.org/pub/linux/utils/kernel/
modutils ] 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 [http://www.tldp.org/HOWTO/Net-HOWTO/index.html]
Linux NET HOWTO and the [http://www.tldp.org/LDP/nag2/index.html] Network
Administrator's Guide . Also check out the [http://www.ecst.csuchico.edu/
~dranch/LINUX/index-linux.html#TrinityOS] 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, [http://www.tldp.org/HOWTO/PPP-HOWTO/index.html] Linux PPP
HOWTO, and [http://www.ecst.csuchico.edu/~dranch/LINUX/index-linux.html#
TrinityOS] TrinityOS. Other helpful HOWTOs could include: Linux DHCP
mini-HOWTO, [http://www.tldp.org/HOWTO/Cable-Modem/index.html] Linux
Cable Modem mini-HOWTO and [http://www.tldp.org/HOWTO/DSL-HOWTO/
index.html] 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. ** "

* 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 [http://www.netfilter.org/documentation/
pomlist/pom-summary.html] 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] 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] http://www.netfilter.org/
documentation/index.html#HOWTO and more specifically [http://
www.netfilter.org/documentation/HOWTO//NAT-HOWTO.html] 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/] 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/] 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 [http://
www.netfilter.org/] Unreliable IPTABLES HOWTOs page.


* Loadable kernel modules, preferably 2.1.121 or higher, are available from
[http://home.pi.se/blox/modutils/index.html] http://home.pi.se/blox/
modutils/index.html or [ftp://ftp.kernel.org/pub/linux/utils/kernel/
modutils ] 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 [http://www.tldp.org/HOWTO/Net-HOWTO/index.html]
Linux NET HOWTO and the [http://www.tldp.org/LDP/nag2/index.html] Network
Administrator's Guide . Also check out the [http://www.ecst.csuchico.edu/
~dranch/LINUX/index-linux.html#TrinityOS] 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, [http://www.tldp.org/HOWTO/PPP-HOWTO/index.html] Linux PPP
HOWTO, and [http://www.ecst.csuchico.edu/~dranch/LINUX/index-linux.html#
TrinityOS] TrinityOS. Other helpful HOWTOs could include: Linux DHCP
mini-HOWTO, [http://www.tldp.org/HOWTO/Cable-Modem/index.html] Linux
Cable Modem mini-HOWTO and [http://www.tldp.org/HOWTO/DSL-HOWTO/
index.html] 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.

Source: CoolInterview.com

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