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I'd like to migrate my old pure iptables firewall configuration to a shorewall setup. I get the basics, but I haven't been able to replicate my existing knockd setup:

  • I have a 'tmpknock' chain that opens some ports, e.g. port 22, for 30 seconds (multiple IPs allowed at the same time in the tmpknock chain, if multiple people try to log in simultaneously!).
  • I have a 'permknock' chain that opens some ports (e.g. 80) forever, but only to one IP at a time (which gets replaced, when the next one tries to knock from a different IP - this allows me to test some services which are not currently open to the public)

The setup in /etc/knockd.conf is simple:

[tmpAndPermKnock]
    sequence      = 10000,11000,12000
    seq_timeout   = 9
    tcpflags      = syn
    start_command = /sbin/iptables -I tmpknock -s %IP% -j ACCEPT; 
                    /sbin/iptables -F permknock;
                    /sbin/iptables -I permknock -s %IP% -j ACCEPT
    cmd_timeout   = 30
    stop_command  = /sbin/iptables -D tmpknock -s %IP% -j ACCEPT

Now I can easily link from my existing chains to these chains, e.g.:

iptables -A open-in -p tcp --dport 22 -j tmpknock
iptables -A open-in -p tcp --dport 80 -j permknock

How can I integrate this with a simple shorewall setup? I'm really just starting out with shorewall, and don't know how to perform the jump to my chains. I imagine, it would be something like this:

/etc/shorewall/rules (does not work):

#ACTION         SOURCE        DEST      PROTO      DEST
JUMP(tmpknock)  net           fw        tcp        22
JUMP(permknock) net           fw        tcp        80

... but there's no JUMP action in http://shorewall.net/manpages/shorewall-rules.html ...

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1 Answer 1

There doesn't seem to be a nice solution to this (boo Shorewall) :-/ There seem to be two options:

  1. Write a custom Shorewall module in Perl. There is some documentation on writing modules to implement knocking, either using the recent match target or using manual chains.
  2. Write a start extension script (which is run after Shorewall has setup all its rules) to insert a jump rule to the knock chains in the INPUT chain.
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Thanks for your answer! Option 1: Problem is, I'd like to keep the flexibility to replace knockd easily with something like e.g. cryptknock - so I don't want to rely on special Shorewall programming. / Option 2: Maybe as a last resort... I still hope to find a nicer solution. –  Chris Lercher Jun 1 '12 at 12:02

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