Date: Sat, 12 Sep 2009 16:10:21 +0200 From: Luigi Rizzo <rizzo@iet.unipi.it> To: Cypher Wu <cypher.w@gmail.com> Cc: freebsd-ipfw@freebsd.org Subject: Re: Transparent firewall & Dynamic rules Message-ID: <20090912141021.GA46670@onelab2.iet.unipi.it> In-Reply-To: <f9f38a550909120651t49362b93m83f08e862adc63cb@mail.gmail.com> References: <f9f38a550909120032k2572fd3y30a1a5e5d0b457cd@mail.gmail.com> <20090912130913.GA46135@onelab2.iet.unipi.it> <f9f38a550909120651t49362b93m83f08e862adc63cb@mail.gmail.com>
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On Sat, Sep 12, 2009 at 09:51:04PM +0800, Cypher Wu wrote: > It's seems fine, but I still have some questions: > 1. The endpoint will response to the keepalive TCP segment and the > destination will be the other endpoint, will IPFW just let it though > like the usual IP packet, or try to figure it out and drop it? it will let the packet through. > 2. If I have two computer I can make sure both end are not using > keepalive, then I can still figure out there is a firewall between > these two computers? you can disable the keepalives on the firewall (if there is no sysctl for it, it's a trivial code change anyways), and you can set a large timeout. but by definition the presence of a firewall _is_ detectable, unless it blocks nothing so it is just a logger and not a firewall. 'transparent' referred to a middlebox means "it does not require endpoint reconfiguration", not that it is undetectable.
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