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Thursday January 18, 2007

IPFilter 5.0.0 - feedback requested

So i've been implementing some new features in ipfilter, whether or not they make it a 5.0, I'm not sure...maybe a few people can let me know what they think about that..

So what are these new features?

There are 3 new commands for ipnat.conf:

• rewrite - change both source and address fields for incoming or outgoing packets
• encap - encapsulated the packet in a new IP header (this will be compatible, I hope, with IPENCAP tunnels elsewhere0
• divert - encapsulate the packet into an IP+UDP packet

To help people use these, I've rewritten the ipnat.conf man page.

divert

A divert rule looks like this:

divert in on le0 proto udp from any to any port = 53 -> src 127.0.0.1,54 dst 127.0.0.1,5300;

note the ";" on the end of the line. To the left of the "->" is the original packet to be matched, on the right, the IP/UDP header to create and put in front of the packet. Reply packets from that socket will have the IP+UDP headers removed when they get back to IPFilter. I'm hoping this will provide cross-platform "divert" functionality but it needs more widespread testing than what I've been able to achieve.

encap

encap is pretty much the same as divert, minus the port numbers to the right of "->".

rewrite

Rewrites have a subset of the combined functionality of rdr/map rules. As an example of how the man page has been rewritten, I've included the contents of it for this new command below.

ipmon

You can now use ipmon.conf to as the place to specify how log records are sent to syslog (facility & priority) rather than needing to do it in filter rules.

ipf

As part of the "keep state" options, you can now specify a rule group to which ICMP replies can be filtered by - "... keep state(icmp-head icmprules)"

It is also now possible to position stateful filtering checks, inbound and outbound nat lookups. If this is done, the traditional checks are no longer performed. This is done as follows:

call now fr_checkstate in on le0 from any to any
call now fr_ipfnatin in on ppp0 all
call now fr_ipfnatout out on bge0 from bge0/32 to any

Oh, being 5.0.0, it is a development version, there's nothing release quality about it (well, you might argue that for others too .. >:->), this is just to get some feedback from people on features and enable some people to try/test a few things out beyond my limited scope. Perhaps most importantly, most of my work to date has been limited to using NetBSD.

It can be downloaded from ip_fil5.0.0.tar.gz. MD5 (/home/darrenr/ip_fil5.0.0.tar.gz) = 7798797c1929cb55c182d3088f40b0b5

REWRITING SOURCE AND DESTINATION
       Whilst the above two commands provide a lot of flexibility in changing
       addressing  fields  in packets, often it can be of benefit to translate
       both source and destination at the same time or to  change  the source
       address  on  input  or the destination address on output.  Doing all of
       these things can be accomplished using rewrite NAT rules.

       A rewrite rule requires the same level of packet  matching  as before,
       protocol  and  source/destination  information  but  in addition allows
       either in or out to be specified like this:

       rewrite in on ppp0 proto tcp from any to any port = 80 ->
            src 0/0 dst 127.0.0.1,3128;
       rewrite out on ppp0 from any to any ->
            src 0/32 dst 10.1.1.0/24;

       On the RHS we can specify both new source and  destination information
       to  place  into the packet being sent out.  As with other rules used in
       ipnat.conf, there are shortcuts syntaxes available to use the original
       address  information  (0/0) and the address associated with the network
       interface (0/32.)  For TCP and UDP, both address and  port information
       can  be  changed.   At  present it is only possible to specify either a
       range of port numbers to be used (X-Y) or a single port number (=X) as
       follows:

       rewrite in on le0 proto tcp from any to any port = 80 ->
            src 0/0,2000-20000 dst 127.0.0.1,port = 3128;

       There  are four fields that are stepped through in enumerating  the num-
       ber space available for creating a new destination:

       source address

       source port

       destination address

       destination port

       If one of these happens to be a static then it will be skipped 
       and  the  next one incremented.  As an example:

       rewrite out on le0 proto tcp from any to any port = 80 ->
            src 1.0.0.0/8,5000-5999 dst 2.0.0.0/24,6000-6999;

       The translated packets would be:
       1st src=1.0.0.1,5000 dst=2.0.0.1,6000

       2nd src=1.0.0.2,5000 dst=2.0.0.1,6000

       3rd src=1.0.0.2,5001 dst=2.0.0.1,6000

       4th src=1.0.0.2,5001 dst=2.0.0.2,6000

       5th src=1.0.0.2,5001 dst=2.0.0.2,6001

       6th src=1.0.0.3,5001 dst=2.0.0.2,6001

       and so on.

       As  with  map  rules, it is possible to specify a range of addresses by
       including the word range before the addresses:

       rewrite from any to any port = 80 ->
            src 1.1.2.3 - 1.1.2.6 dst 2.2.3.4 - 2.2.3.6;