questions about netfilter/iptables api

[Abraham vd Merwe <abraham@2d3d.co.za>]

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Hi!

I'm trying to figure out how to prepend rules into the INPUT/OUTPUT chains.
The way I see it, you do

1. getsockopt IPT_SO_GET_INFO and IPT_SO_GET_ENTRIES to get current entries
in chain.

2. construct a ``struct ipt_entry'' with the new rule.

3. construct a ``struct ipt_replace'' entry with new entry + old entries.

4. do setsockopt IPT_SO_SET_REPLACE to insert new entry in the chain.

Now, what I can't figure out is what those hook_entry and underflow arrays
in ``struct ipt_replace'' are used for and what offsets I need to put in them.

Also, I see that iptables goes and appends elems entries for some of the
struct ipt_entry entries. When do I need to do that and is it necessary for
simple rules like these:

-I INPUT -d net/mask -i eth0
-I OUTPUT -s net/mask -o eth1
-I INPUT -d net/mask -p tcp --source-port 23 -i eth0
etc.

I don't see why any additional info would be necessary since you can fit all
that info in the the ``struct ipt_ip'' field.

-- 

Regards
 Abraham

Well, O.K.  I'll compromise with my principles because of EXISTENTIAL DESPAIR!

__________________________________________________________
 Abraham vd Merwe - 2d3D, Inc.

 Device Driver Development, Outsourcing, Embedded Systems

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