IPFW 'keep state' & 'limit'

[Dan Pelleg]

"fbsd_user" <fbsd_user at a1poweruser.com> writes:

> The FBSD 5.2 man IPFW does not say anything different that the 4.9
> man IPFW.
> Are you saying the man doc in 5.2 is wrong?
>
> 5.2 is using the ipfw2 code for IPFIREWALL I believe.
>
> Documenting the fact that 'limit' performs the same function as
> 'keep state' in additional to 'limit' stated purpose is very
> important information. Also that 'limit' and 'keep state' can not be
> coded together is another very important piece information that need
> to be documented in the man IPFW data.
>
> Should this be submitted as an problem report?
>
>
>
> -----Original Message-----
> From: Dan Pelleg [mailto:daniel+bsd at pelleg.org]
> Sent: Wednesday, January 14, 2004 9:47 AM
> To: fbsd_user at a1poweruser.com
> Cc: freebsd-questions at FreeBSD. ORG
> Subject: Re: IPFW 'keep state' & 'limit'
>
> "fbsd_user" <fbsd_user at a1poweruser.com> writes:
>
>> Reading the man page on IPFW rule syntax, I get the impression
> that
>> the 'limit' option uses the stateful dynamic rules table. But it's
>> unclear whether 'keep state' and limit can be used on the same
> rule,
>> or if the limit option performs the 'keep state' function in
>> addition to the limit function.
>>
>> So as an example
>>
>> $cmd 00390 allow tcp from any to any 22 in via dc0 setup
> keep-state
>> limit src-addr 3
>>
>> will this work?
>>
>
> limit implies keep-state, and you should really specify one or the
> other. If you specify both, ipfw won't complain, but ipfw2 will. So
> it's
> best to not do that.
>
> --
>
>   Dan Pelleg
>
>
>

Your rule, given to IPFW2 (on a 4.X system), yields:

ipfw: only one of keep-state and limit is allowed

I wouldn't say the man page hides the first fact; it is reasonably careful
to say "keep-state or limit" in most places. 

It does, however, not mention that specifying both in the same rule is not
accepted. In fact it says that "Zero or more" rule options are accepted,
with both limit and keep-state listed as options (in the RULE OPTIONS
section - this is on a man page from around 5.1). Given this might surprise
people who move to 5.X and even lock them out, it might also be worth
mentioning in one of migration guides. I suggest you bring this up to the
doc@ list.

-- 

  Dan Pelleg