0fbf800481
offset is non-zero:
- Do not match fragmented packets if the rule specifies a port or
TCP flags
- Match fragmented packets if the rule does not specify a port and
TCP flags
Since ipfw cannot examine port numbers or TCP flags for such packets,
it is now illegal to specify the 'frag' option with either ports or
tcpflags. Both kernel and ipfw userland utility will reject rules
containing a combination of these options.
BEWARE: packets that were previously passed may now be rejected, and
vice versa.
Reviewed by: Archie Cobbs <archie@whistle.com>
529 lines
13 KiB
Groff
529 lines
13 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
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.Ar 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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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 your 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 or flushing, be quiet about actions (implies '-f'). This is
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useful for adjusting rules by executing multiple ipfw commands in a script
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(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.
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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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.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 hacker.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 hacker.evil.org to wolf.tambov.su 23
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.Pp
|
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This one disallows any connection from the entire hackers 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 divert 4 ,
|
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.Xr ip 4 ,
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.Xr ipfirewall 4 ,
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.Xr protocols 5 ,
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.Xr services 5 ,
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.Xr reboot 8 ,
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.Xr sysctl 8 ,
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.Xr syslogd 8
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.Sh BUGS
|
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.Pp
|
|
.Em WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!
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.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
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|
do
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.Em NOT
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|
do anything you don't understand.
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|
.Pp
|
|
When manipulating/adding chain entries, service and protocol names are
|
|
not accepted.
|
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.Pp
|
|
Incoming packet fragments diverted by
|
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.Ar divert
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are reassembled before delivery to the socket, whereas fragments diverted via
|
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.Ar tee
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are not.
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.Pp
|
|
Port aliases containing dashes cannot be first in a list.
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.Sh AUTHORS
|
|
Ugen J. S. Antsilevich,
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Poul-Henning Kamp,
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Alex Nash,
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Archie Cobbs.
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|
API based upon code written by Daniel Boulet for BSDI.
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.Sh HISTORY
|
|
.Nm
|
|
first appeared in
|
|
.Fx 2.0 .
|