All I have is one packet!

[Vadim Goncharov]

06.08.07 @ 23:05 Eduardo Meyer wrote:

> I have tried, for many weeks, ng_tag to tag packets for ipfw
> filtering. I could make it work fine. However, I have one problem. I
> want to make a state that will match any packet, on any protocol,
> between the peers. Why? Because all I have, is one packet. And this
> packet however, wont always be in the same transport protocol.
>
> For example, I can identify session initialization on TCP packets, but
> once initialized, all communication between peers happen via UDP.
>
> I know such a thing dont exist in ipfw. However, I would like to know
> if someone can suggest changes to the code that would do this. Would
> also be great if I could have a sysctl OID to tune state-timing of
> this unusual behavior, differently from the existing sysctl mibs on
> "dyn" stuff on ipfw.
>
> Every suggestion on a feature like that, would be appreciated.

Yes, dynamic rules in ipfw are not intended for supporting state created  
in the middle of the session, wuth the default sysctl settings it will be  
kept for 1 second (which, however, is enough for shaping of fast  
transfers). I think, precise controlling of dynamic rules from both  
userland and kernel should be added to ipfw, to modify existing rules on  
the fly (or even more features, like pfsync). As a hackish dirty  
workaround, may be it should be only one keyword, something like  
"keep-state-middle", to create normal dynamic rule without initial SYNs.

But you've said about even more complex behaviour, like init on TCP,  
continue with UDP. That's difficult to implement in kernel, and may be  
even not suitable for ipfw. Currently (I think), you can try to emulate  
this behaviour by divert'ing tagged by ng_tag packet to userland program,  
like snort_inline (from ports collection) with needed scripting, which  
will trigger adding proper rules to firewall (you should also care about  
expiring that connection on SYNs and RSTs, though).

-- 
WBR, Vadim Goncharov