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f607e2c314
synonym for '-a list'; stop SEGV when specifying 'via' with no interface; change 2 instances of strcpy() to strncpy(). This is a candidate for 2.2
379 lines
9.2 KiB
Groff
379 lines
9.2 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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.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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.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 numbered 100 higher
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than the previous rule. If the highest defined rule number is
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greater than 65434, 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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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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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. This option is the only way to see
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accounting records.
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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, it prints a message. 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.
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.It Ar pass
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Same as allow.
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.It Ar accept
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Same as allow.
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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 deny
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Discard packets that match this rule.
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The search terminates.
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.It Ar reject
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Discard packets that match this rule, and try to send an ICMP notice.
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The search terminates.
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.It Ar divert port
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Divert packets that match this rule to the divert socket bound to port
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.Ar port .
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The search terminates.
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.El
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.Pp
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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 IP_FIREWALL_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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.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.
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.It Ar all
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All packets match.
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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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.Pp
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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
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.Em protocols ,
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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 not be used instead of a numeric port value.
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Also, note that a range may only be specified as the first value,
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and 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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If ``via''
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.Ar name
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is specified, only packets received via or on their way out of an interface
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matching
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.Ar name
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will match this rule.
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.Pp
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If ``via''
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.Ar ipno
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is specified, only packets received via or on their way out of an interface
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having the address
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.Ar ipno
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will match this rule.
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.Pp
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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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.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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.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 good usage of list command to see accounting records:
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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
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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 syslogd 8
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.Sh BUGS
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.Pp
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.Em WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!
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.Pp
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This program can put your computer in rather unusable state. When
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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
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When manipulating/adding chain entries, service and protocol names are
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not accepted.
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.Sh AUTHORS
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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
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.Nm
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first appeared in
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.Fx 2.0 .
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