Request: Submission of Rulesets

Thomas Jones admin at
Thu Aug 25 16:35:47 CEST 2005

Hash: SHA1

On Thursday 25 August 2005 06:56, Derick Anderson wrote:
> Out of curiosity (and the lack of fully understanding your intent), how
> would this DTD validate a ruleset? I imagine you'd be trying to go
> beyond syntax since netfilter will tell you when you do something silly
> like a --dport without a -p tcp|udp anyway. If that's so, what is your
> standard for failure of a ruleset? Or success of a ruleset?

The DTD is simply the document model by which the rule and/or rulesets can be 
applied against. 

This project can in no way perform logical evaluation of the rules. By this I 
mean the following: say you want to rate-limit incoming type 8 ping messages. 
To do so you would construct the following rules:

iptables -A INPUT -i eth0 -p icmp --icmp-type echo-request \
              -m limit --limit 1/second -j ACCEPT

iptables -A INPUT -i eth0 -p icmp --icmp-type echo-request -j DROP

Using logical evaluation of these rules, we can determine the following with 
respect to the pair:

- - Utilization of one rule without the other results in a completely different 
- - They must be introduced to netfilter in the order they are given -- 
otherwise the same is true again.
- - Both rules should be introduced adjacently. Otherwise there is chance for 
another rule to intervene.

None of this can be performed by a DTD or an XML markup language. These 
however can be evaluated as you say by use of an XSL stylesheet.

The DTD simply validates against a known and programmed structure. The 
advantages of using XML and this approach are such:

- - Easy to develop according to the structured document model.
- - Anybody can construct new rules with a minimal effort of syntactical 
- - The netfiler rules can be processed with a custom stylesheet to produce 
equivalent rules and/or rulesets in other forms for perimeter devices not 
consistent with the netfilter syntax(other firewalls, routers, etc...).
- - The netfiler rules can be processed with a custom stylesheet to evaluate the 
logical structure/intent of a given ruleset.
- - The rules can be digitally signed and encrypted by the administrative entity 
to secure the content. This ensures that confidentiality and integrity of the 
resources are intact.
- - The XML Security function(s) are standards-based. So inclusion into 
regulatory requirements can be easily introduced without complications. i.e. 

> I can submit
> a working ruleset that isn't optimal (accepting RELATED,ESTABLISHED
> connections as the last rule, for example) or that checks src/dst IPs
> but not which interface...

I am not here to judge yourself or the logical purpose of your rules. I simply 
want to contribute to the community. None of my projects are for profit. 
However, I do think that it could be a good starting point for new users to 
the netfilter framework to be able to construct valid rules and/or rulesets.

> Admittedly I don't know that much about XML and DTDs. I don't know how
> powerful DTDs can be, but it seems to me like you'd need a high-level
> programming language in order to test for more than syntactical
> correctness. 

That is a totally different beast. This is where the XSL stylesheets come into 

> A simulation environment for Netfilter rules is something
> I'd really like to see.

Agreed. Construction of pseudo datagrams and testing for resultant outcomes 
would be a very interesting project. 

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