Date: Thu, 04 Jun 2009 22:33:26 -0700 From: Julian Elischer <julian@elischer.org> To: Freddie Cash <fjwcash@gmail.com> Cc: freebsd-ipfw@freebsd.org Subject: Re: Rules processing in ipfw: processing ends with rule 65535 or first match? Message-ID: <4A28AE26.6010805@elischer.org> In-Reply-To: <b269bc570906041523v2076ec83y90a9b8474199f457@mail.gmail.com> References: <b269bc570906041523v2076ec83y90a9b8474199f457@mail.gmail.com>
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Freddie Cash wrote:
> Over the years, various how-tos and docs that I've read comparing ipfw
> to ipf and pf have categorised them as such:
>
> - ipf/pf compares the packet against every rule in the ruleset, and
> the last matching action is used once the end of the ruleset is
> reached (last-match-wins)
>
> - ipfw compares the packet against the rules, and stops processing
> the rulesset once a rule matches (first-match-wins)
>
> And, if one wants to get the ipfw behaviour in ipf/pf, they can use
> the "quick" keyword, which stops processing of the ruleset as soon as
> one of those rules matches.
>
> IOW, for a ruleset with 1000 rules, ipf/pf will scan every single rule
> for every single packet; and ipfw will only scan the ruleset up to the
> first matching rule. In theory, the ipfw method would be a lot
> faster, and less intensive.
>
> However, reading through the man page for ipfw(8) on FreeBSD 7.2, it
> lists the following (Description section):
> The packet passed to the firewall is compared against each
> of the rules in the firewall ruleset. When a match is found, the action
> corresponding to the matching rule is performed.
the packet is compared against each rule it encounters
however it might not encounter a rule by 3 means:
1/ it matches a rule before the rule in question and stops processing
2/ it bypasses the rule in question due to matching a rule with a
skipto action.
3/ it matches a check-state rule and effectively shortcuts to the
exact rule that is needed for that session, skipping all
intermediate rles.
>
> And, later, in the Packet Flow section:
> Also note that each packet is always checked against the complete rule-
> set, irrespective of the place where the check occurs, or the source of
> the packet.
>
> These make it sound like ifpw processes the entire ruleset for every
> packet, regardless of when a match occurs.
>
> So, which is it? Is ipfw a first-match-wins and rule processing ends
> setup? Or does it check every single rule for every single packet?
>
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