597 lines
15 KiB
Groff
597 lines
15 KiB
Groff
.Dd July 20, 1996
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.Dt IPFW 8 SMM
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.Os FreeBSD
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.Sh NAME
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.Nm ipfw
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.Nd controlling utility for IP firewall
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.Sh SYNOPSIS
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.Nm ipfw
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.Op Fl q
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.Oo
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.Fl p Ar preproc
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.Op Fl D Ar macro Ns Op Ns =value
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.Op Fl U Ar macro
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.Oc
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file
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.Nm ipfw
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.Oo
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.Fl f
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.Fl q
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.Oc
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flush
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.Nm ipfw
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.Oo
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.Fl q
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.Oc
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zero
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.Op Ar number ...
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.Nm ipfw
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delete
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.Ar number ...
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.Nm ipfw
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.Op Fl aftN
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list
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.Op Ar number ...
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.Nm ipfw
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.Oo
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.Fl ftN
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.Oc
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show
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.Op Ar number ...
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.Nm ipfw
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.Oo
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.Fl q
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.Oc
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add
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.Op Ar number
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.Ar action
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.Op log
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.Ar proto
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from
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.Ar src
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to
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.Ar dst
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.Op via Ar name | ipno
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.Op Ar options
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.Sh DESCRIPTION
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If used as shown in the first synopsis line, the
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.Ar file
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will be read line by line and applied as arguments to the
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.Nm
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command.
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.Pp
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Optionally, a preprocessor can be specified using
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.Fl p Ar preproc
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where
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.Ar file
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is to be piped through. Useful preprocessors include
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.Xr cpp 1
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and
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.Xr m4 1 .
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If
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.Ar preproc
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doesn't start with a slash as its first character, the usual
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.Ev PATH
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name search is performed. Care should be taken with this in environments
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where not all filesystems are mounted (yet) by the time
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.Nm
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is being run (e. g. since they are mounted over NFS). Once
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.Fl p
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has been specified, optional
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.Fl D
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and
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.Fl U
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specifcations can follow and will be passed on to the preprocessor.
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This allows for flexible configuration files (like conditionalizing
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them on the local hostname) and the use of macros to centralize
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frequently required arguments like IP addresses.
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.Pp
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The
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.Nm
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code works by going through the rule-list for each packet,
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until a match is found.
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All rules have two associated counters, a packet count and
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a byte count.
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These counters are updated when a packet matches the rule.
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.Pp
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The rules are ordered by a ``line-number'' from 1 to 65534 that is used
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to order and delete rules. Rules are tried in increasing order, and the
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first rule that matches a packet applies.
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Multiple rules may share the same number and apply in
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the order in which they were added.
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.Pp
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If a rule is added without a number, it is numbered 100 higher
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than the previous rule. If the highest defined rule number is
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greater than 65534, new rules are appended to the last rule.
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.Pp
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The delete operation deletes the first rule with number
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.Ar number ,
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if any.
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.Pp
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The list command prints out the current rule set.
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.Pp
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The show command is equivalent to `ipfw -a list'.
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.Pp
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The zero operation zeroes the counters associated with rule number
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.Ar number .
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.Pp
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The flush operation removes all rules.
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.Pp
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Any command beginning with a '#', or being all blank, is ignored.
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.Pp
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One rule is always present:
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.Bd -literal -offset center
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65535 deny all from any to any
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.Ed
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.Pp
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This rule is the default policy, i.e., don't allow anything at all.
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Your job in setting up rules is to modify this policy to match your
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needs.
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.Pp
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However, if the kernel option
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.Dq IPFIREWALL_DEFAULT_TO_ACCEPT
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is active, the rule is instead:
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.Bd -literal -offset center
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65535 allow all from any to any
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.Ed
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.Pp
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This variation lets everything pass through. This option should only be
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activated in particular circumstances, such as if you use the firewall
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system as an on-demand denial-of-service filter that is normally wide open.
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.Pp
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The following options are available:
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.Bl -tag -width flag
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.It Fl a
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While listing, show counter values. See also ``show'' command.
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.It Fl f
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Don't ask for confirmation for commands that can cause problems if misused
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(ie; flush).
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.Ar Note ,
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if there is no tty associated with the process, this is implied.
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.It Fl q
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While adding, zeroing or flushing, be quiet about actions (implies '-f').
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This is useful for adjusting rules by executing multiple ipfw commands in a
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script (e.g. sh /etc/rc.firewall), or by processing a file of many ipfw rules,
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across a remote login session. If a flush is performed in normal
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(verbose) mode (with the default kernel configuration), it prints a message.
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Because all rules are flushed, the
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message cannot be delivered to the login session, the login session is
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closed and the remainder of the ruleset is not processed. Access to the
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console is required to recover.
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.It Fl t
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While listing, show last match timestamp.
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.It Fl N
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Try to resolve addresses and service names in output.
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.El
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.Pp
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.Ar action :
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.Bl -hang -offset flag -width 1234567890123456
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.It Ar allow
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Allow packets that match rule.
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The search terminates. Aliases are
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.Ar pass ,
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.Ar permit ,
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and
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.Ar accept .
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.It Ar deny
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Discard packets that match this rule.
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The search terminates.
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.Ar Drop
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is an alias for
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.Ar deny .
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.It Ar reject
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(Deprecated.) Discard packets that match this rule, and try to send an ICMP
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host unreachable notice.
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The search terminates.
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.It Ar unreach code
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Discard packets that match this rule, and try to send an ICMP
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unreachable notice with code
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.Ar code ,
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where
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.Ar code
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is a number from zero to 255, or one of these aliases:
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.Ar net ,
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.Ar host ,
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.Ar protocol ,
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.Ar port ,
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.Ar needfrag ,
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.Ar srcfail ,
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.Ar net-unknown ,
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.Ar host-unknown ,
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.Ar isolated ,
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.Ar net-prohib ,
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.Ar host-prohib ,
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.Ar tosnet ,
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.Ar toshost ,
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.Ar filter-prohib ,
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.Ar host-precedence ,
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or
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.Ar precedence-cutoff .
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The search terminates.
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.It Ar reset
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TCP packets only. Discard packets that match this rule,
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and try to send a TCP reset (RST) notice.
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The search terminates.
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.It Ar count
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Update counters for all packets that match rule.
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The search continues with the next rule.
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.It Ar divert port
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Divert packets that match this rule to the
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.Xr divert 4
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socket bound to port
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.Ar port .
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The search terminates.
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.It Ar tee port
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Send a copy of packets matching this rule to the
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.Xr divert 4
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socket bound to port
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.Ar port .
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The search continues with the next rule. This feature is not yet implemeted.
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.It Ar fwd ipaddr Op ,port
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Change the next-hop on matching packets to
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.Ar ipaddr ,
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which can be an IP address in dotted quad or a host name.
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If
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.Ar ipaddr
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is not a directly-reachable address, the route
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as found in the local routing table for that IP is used
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instead.
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If
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.Ar ipaddr
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is a local address, then on a packet entering the system from a remote
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host it will be diverted to
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.Ar port
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on the local machine, keeping the local address of the socket set
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to the original IP address the packet was destined for. This is intended
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for use with transparent proxy servers. If the IP is not
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a local address then the port number (if specified) is ignored and
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the rule only applies to packets leaving the system. This will
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also map addresses to local ports when packets are generated locally.
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The search terminates if this rule matches. If the port number is not
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given then the port number in the packet is used, so that a packet for
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an external machine port Y would be forwarded to local port Y. The kernel
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must have been compiled with optiions IPFIREWALL_FORWARD.
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.It Ar skipto number
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Skip all subsequent rules numbered less than
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.Ar number .
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The search continues with the first rule numbered
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.Ar number
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or higher.
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.El
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.Pp
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If a packet matches more than one
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.Ar divert
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and/or
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.Ar tee
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rule, all but the last are ignored.
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.Pp
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If the kernel was compiled with
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.Dv IPFIREWALL_VERBOSE ,
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then when a packet matches a rule with the ``log''
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keyword a message will be printed on the console.
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If the kernel was compiled with the
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.Dv IPFIREWALL_VERBOSE_LIMIT
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option, then logging will cease after the number of packets
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specified by the option are received for that particular
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chain entry. Logging may then be re-enabled by clearing
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the packet counter for that entry.
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.Pp
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Console logging and the log limit are adjustable dynamically
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through the
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.Xr sysctl 8
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interface.
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.Pp
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.Ar proto :
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.Bl -hang -offset flag -width 1234567890123456
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.It Ar ip
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All packets match. The alias
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.Ar all
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has the same effect.
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.It Ar tcp
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Only TCP packets match.
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.It Ar udp
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Only UDP packets match.
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.It Ar icmp
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Only ICMP packets match.
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.It Ar <number|name>
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Only packets for the specified protocol matches (see
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.Pa /etc/protocols
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for a complete list).
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.El
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.Pp
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.Ar src
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and
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.Ar dst :
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.Bl -hang -offset flag
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.It Ar <address/mask>
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.Op Ar ports
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.El
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.Pp
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The
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.Em <address/mask>
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may be specified as:
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.Bl -hang -offset flag -width 1234567890123456
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.It Ar ipno
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An ipnumber of the form 1.2.3.4.
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Only this exact ip number match the rule.
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.It Ar ipno/bits
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An ipnumber with a mask width of the form 1.2.3.4/24.
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In this case all ip numbers from 1.2.3.0 to 1.2.3.255 will match.
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.It Ar ipno:mask
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An ipnumber with a mask width of the form 1.2.3.4:255.255.240.0.
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In this case all ip numbers from 1.2.0.0 to 1.2.15.255 will match.
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.El
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.Pp
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The sense of the match can be inverted by preceding an address with the
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``not'' modifier, causing all other addresses to be matched instead. This
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does not affect the selection of port numbers.
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.Pp
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With the TCP and UDP protocols, optional
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.Em ports
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may be specified as:
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.Pp
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.Bl -hang -offset flag
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.It Ns {port|port-port} Ns Op ,port Ns Op ,...
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.El
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.Pp
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Service names (from
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.Pa /etc/services )
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may be used instead of numeric port values.
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A range may only be specified as the first value,
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and the length of the port list is limited to
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.Dv IP_FW_MAX_PORTS
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(as defined in
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.Pa /usr/src/sys/netinet/ip_fw.h )
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ports.
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.Pp
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Fragmented packets which have a non-zero offset (i.e. not the first
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fragment) will never match a rule which has one or more port
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specifications. See the
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.Ar frag
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option for details on matching fragmented packets.
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.Pp
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Rules can apply to packets when they are incoming, or outgoing, or both.
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The
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.Ar in
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keyword indicates the rule should only match incoming packets.
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The
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.Ar out
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keyword indicates the rule should only match outgoing packets.
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.Pp
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To match packets going through a certain interface, specify
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the interface using
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.Ar via :
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.Bl -hang -offset flag -width 1234567890123456
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.It Ar via ifX
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Packet must be going through interface
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.Ar ifX.
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.It Ar via if*
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Packet must be going through interface
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.Ar ifX ,
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where X is any unit number.
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.It Ar via any
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Packet must be going through
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.Em some
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interface.
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.It Ar via ipno
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Packet must be going through the interface having IP address
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.Ar ipno .
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.El
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.Pp
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The
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.Ar via
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keyword causes the interface to always be checked.
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If
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.Ar recv
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or
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.Ar xmit
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is used instead of
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.Ar via ,
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then the only receive or transmit interface (respectively) is checked.
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By specifying both, it is possible to match packets based on both receive
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and transmit interface, e.g.:
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.Pp
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.Dl "ipfw add 100 deny ip from any to any out recv ed0 xmit ed1"
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.Pp
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The
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.Ar recv
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interface can be tested on either incoming or outgoing packets, while the
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.Ar xmit
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interface can only be tested on outgoing packets. So
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.Ar out
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is required (and
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.Ar in
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invalid) whenver
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.Ar xmit
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is used. Specifying
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.Ar via
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together with
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.Ar xmit
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or
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.Ar recv
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is invalid.
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.Pp
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A packet may not have a receive or transmit interface: packets originating
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from the local host have no receive interface. while packets destined for
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the local host have no transmit interface.
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.Pp
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Additional
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.Ar options :
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.Bl -hang -offset flag -width 1234567890123456
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.It frag
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Matches if the packet is a fragment and this is not the first fragment
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of the datagram.
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.Ar frag
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may not be used in conjunction with either
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.Ar tcpflags
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or TCP/UDP port specifications.
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.It in
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Matches if this packet was on the way in.
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.It out
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Matches if this packet was on the way out.
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.It ipoptions Ar spec
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Matches if the IP header contains the comma separated list of
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options specified in
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.Ar spec .
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The supported IP options are:
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.Ar ssrr
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(strict source route),
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.Ar lsrr
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(loose source route),
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.Ar rr
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(record packet route), and
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.Ar ts
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(timestamp).
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The absence of a particular option may be denoted
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with a ``!''.
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.It established
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Matches packets that have the RST or ACK bits set.
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TCP packets only.
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.It setup
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Matches packets that have the SYN bit set but no ACK bit.
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TCP packets only.
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.It tcpflags Ar spec
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Matches if the TCP header contains the comma separated list of
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flags specified in
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.Ar spec .
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The supported TCP flags are:
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.Ar fin ,
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.Ar syn ,
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.Ar rst ,
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.Ar psh ,
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.Ar ack ,
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and
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.Ar urg .
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The absence of a particular flag may be denoted
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with a ``!''.
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A rule which contains a
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.Ar tcpflags
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specification can never match a fragmented packet which has
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a non-zero offset. See the
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.Ar frag
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option for details on matching fragmented packets.
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.It icmptypes Ar types
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Matches if the ICMP type is in the list
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.Ar types .
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The list may be specified as any combination of ranges
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or individual types separated by commas.
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.El
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.Sh CHECKLIST
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Here are some important points to consider when designing your
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rules:
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.Bl -bullet -hang -offset flag
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.It
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Remember that you filter both packets going in and out.
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Most connections need packets going in both directions.
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.It
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Remember to test very carefully.
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It is a good idea to be near the console when doing this.
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.It
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Don't forget the loopback interface.
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.El
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.Sh FINE POINTS
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There is one kind of packet that the firewall will always discard,
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that is an IP fragment with a fragment offset of one.
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This is a valid packet, but it only has one use, to try to circumvent
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firewalls.
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.Pp
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If you are logged in over a network, loading the LKM version of
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.Nm
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is probably not as straightforward as you would think.
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I recommend this command line:
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.Bd -literal -offset center
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modload /lkm/ipfw_mod.o && \e
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ipfw add 32000 allow all from any to any
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.Ed
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.Pp
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Along the same lines, doing an
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.Bd -literal -offset center
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ipfw flush
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.Ed
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.Pp
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in similar surroundings is also a bad idea.
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.Pp
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The IP filter list may not be modified if the system security level
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is set to 3 or higher (see
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.Xr init 8
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for information on system security levels).
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.Sh PACKET DIVERSION
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A divert socket bound to the specified port will receive all packets diverted
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to that port; see
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.Xr divert 4 .
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If no socket is bound to the destination port, or if the kernel
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wasn't compiled with divert socket support, diverted packets are dropped.
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.Sh EXAMPLES
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This command adds an entry which denies all tcp packets from
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.Em cracker.evil.org
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to the telnet port of
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.Em wolf.tambov.su
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from being forwarded by the host:
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.Pp
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.Dl ipfw add deny tcp from cracker.evil.org to wolf.tambov.su 23
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.Pp
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This one disallows any connection from the entire crackers network to
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my host:
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.Pp
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.Dl ipfw addf deny all from 123.45.67.0/24 to my.host.org
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.Pp
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Here is a good usage of the list command to see accounting records
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and timestamp information:
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.Pp
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.Dl ipfw -at l
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.Pp
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or in short form without timestamps:
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.Pp
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.Dl ipfw -a l
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.Pp
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This rule diverts all incoming packets from 192.168.2.0/24 to divert port 5000:
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.Pp
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.Dl ipfw divert 5000 all from 192.168.2.0/24 to any in
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.Sh SEE ALSO
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.Xr cpp 1 ,
|
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.Xr m4 1 ,
|
|
.Xr divert 4 ,
|
|
.Xr ip 4 ,
|
|
.Xr ipfirewall 4 ,
|
|
.Xr protocols 5 ,
|
|
.Xr services 5 ,
|
|
.Xr init 8 ,
|
|
.Xr reboot 8 ,
|
|
.Xr sysctl 8 ,
|
|
.Xr syslogd 8
|
|
.Sh BUGS
|
|
.Pp
|
|
.Em WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!
|
|
.Pp
|
|
This program can put your computer in rather unusable state. When
|
|
using it for the first time, work on the console of the computer, and
|
|
do
|
|
.Em NOT
|
|
do anything you don't understand.
|
|
.Pp
|
|
When manipulating/adding chain entries, service and protocol names are
|
|
not accepted.
|
|
.Pp
|
|
Incoming packet fragments diverted by
|
|
.Ar divert
|
|
are reassembled before delivery to the socket, whereas fragments diverted via
|
|
.Ar tee
|
|
are not.
|
|
.Pp
|
|
Port aliases containing dashes cannot be first in a list.
|
|
.Pp
|
|
The ``tee'' action is unimplemented.
|
|
.Sh AUTHORS
|
|
.An Ugen J. S. Antsilevich ,
|
|
.An Poul-Henning Kamp ,
|
|
.An Alex Nash ,
|
|
.An Archie Cobbs .
|
|
API based upon code written by
|
|
.An Daniel Boulet
|
|
for BSDI.
|
|
.Sh HISTORY
|
|
.Nm
|
|
first appeared in
|
|
.Fx 2.0 .
|