ipfw fwd layer2/ftp proxy

Ganbold ganbold at micom.mng.net
Fri May 23 03:05:39 UTC 2008

Julian Elischer wrote:
> Ganbold wrote:
>> Hi there,
>> I'm having trouble allowing ftp connections through ipfw (default 
>> deny) enabled bridge firewall.
>> I'm wondering whether it is possible to have some kind of transparent 
>> ftp proxy in such case.
>> Is there anyway I can allow ftp proxying without layer2 forwarding on 
>> ipfw bridge?
>> I thought of forwarding packets in layer2, however it seems like ipfw 
>> still doesn't support that.
>> I saw old patches of luigi@ and if somebody already has adapted that 
>> patch for RELENG_6/7 please let me know.
> I have such patches for the old 'bridge' code that allow bridges to
> intercept IP sessions but not for the new 'if_bridge' code.
> The trick is to make a 'fwd localhost' on the Layer2 ipfw pass
> to result in the packet being passed to the IP stack regardless
> of where the header says it should go.
> In the IP stack a similar 'fwd localhost' rule (maybe the same one)
> will also trigger on the Layer 3 pass, and actually cause teh session 
> to connect.
> For fully transparent (in both directions) you need to alter the IP 
> code to allow you to bind the outgoing socket to a non-local address,
> and to capture the return packets you leed the L2 pirewall pass to
> do a test for 'uid' which has the side affect of noticing whether or
> not there is a local socket that matches a packet, even if it has
> a non  local address on it.

Can you share your patch for old bride code?

Yesterday I tried to look at ip_fw2.c and ip_input.c codes, but it is still
new to me.



>> I know my last try is to deny everything I don't want and then allow 
>> the rest. However I would
>> like to make it work in current configuration.
>> Please let me know your ideas.
>> thanks in advance,
>> Ganbold
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Your fault - core dumped

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