_or_ you may specify "log logamount number" to set logging specifically the rule. In addition, "ipfw resetlog" has been added, which will reset the logging counters on any/all rule(s). ipfw resetlog does not affect the packet/byte counters (as ipfw reset does), and is the only "set" command that can be run at securelevel >= 3. This should address complaints about not being able to set logging amounts, not being able to restart logging at a high securelevel, and not being able to just reset logging without resetting all of the counters in a rule.
771 lines
18 KiB
Groff
771 lines
18 KiB
Groff
.\"
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.\" $Id: ipfw.8,v 1.54 1999/06/19 18:43:18 green Exp $
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.\"
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.Dd July 20, 1996
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.Dt IPFW 8
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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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.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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.Oo
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.Fl q
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.Oc
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resetlog
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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 Op Ar logamount Ar number
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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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specifications 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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Each packet that has been received or is about to be sent goes through
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the
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.Nm
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rules. In the case of a host acting as a gateway, packets that are
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forwarded by the host are processed by
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.Nm
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twice
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.Po
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once when entering, and once when leaving
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.Pc .
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Each packet can be filtered based on the following information that is
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associated with it:
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.Pp
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.Bl -tag -offset indent -compact -width xxxx
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.It Receive Interface Pq Ar recv
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Interface over which the packet was received
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.It Transmit Interface Pq Ar xmit
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Interface over which the packet would be transmitted
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.It Incoming Pq Ar in
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Packet was just received
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.It Outgoing Pq Ar out
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Packet would be transmitted
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.It Source IP Address
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Sender's IP Address
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.It Destination IP Address
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Target's IP Address
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.It Protocol
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IP protocol, including but not limited to IP
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.Pq Ar ip ,
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UDP
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.Pq Ar udp ,
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TCP
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.Pq Ar tcp ,
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or
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ICMP
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.Pq Ar icmp
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.It Source Port
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Sender's UDP or TCP port
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.It Destination Port
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Target's UDP or TCP port
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|
.It Connection Setup Flag Pq Ar setup
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|
This packet is a request to setup a TCP connection
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.It Connection Established Flag Pq Ar established
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|
This packet is part of an established TCP connection
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.It All TCP Flags Pq Ar tcpflags
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|
One or more of the TCP flags: close connection
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.Pq Ar fin ,
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|
open connection
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|
.Pq Ar syn ,
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|
reset connection
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.Pq Ar rst ,
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|
push
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.Pq Ar psh ,
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acknowledgment
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.Pq Ar ack ,
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and
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urgent
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.Pq Ar urg
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.It Fragment Flag Pq Ar frag
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|
This packet is a fragment of an IP packet
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.It IP Options Pq Ar ipoptions
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One or more of the IP options: strict source route
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.Pq Ar ssrr ,
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loose source route
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.Pq Ar lsrr ,
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|
record route
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.Pq Ar rr ,
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|
and timestamp
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.Pq Ar ts
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|
.It ICMP Types Pq Ar icmptypes
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One or more of the ICMP types: echo reply
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.Pq Ar 0 ,
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destination unreachable
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.Pq Ar 3 ,
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source quench
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.Pq Ar 4 ,
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redirect
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|
.Pq Ar 5 ,
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echo request
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.Pq Ar 8 ,
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router advertisement
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.Pq Ar 9 ,
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router solicitation
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|
.Pq Ar 10 ,
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|
time-to-live exceeded
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.Pq Ar 11 ,
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IP header bad
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.Pq Ar 12 ,
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timestamp request
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.Pq Ar 13 ,
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timestamp reply
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.Pq Ar 14 ,
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information request
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.Pq Ar 15 ,
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information reply
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.Pq Ar 16 ,
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address mask request
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.Pq Ar 17 ,
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and address mask reply
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.Pq Ar 18
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.El
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.Pp
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Note that may be dangerous to filter on the source IP address or
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source TCP/UDP port because either or both could easily be spoofed.
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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
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.Dq line-number
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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 than the highest
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defined rule number, unless the highest defined rule number is 65435 or
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greater, in which case new rules are given that same number.
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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
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.Sq 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 resetlog operation resets the logging counters associated with
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|
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
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.Sq # ,
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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 indent
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.It Fl a
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While listing, show counter values. See also
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.Dq show
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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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(i.e. 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, resetlogging or flushing, be quiet about actions (implies
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.Fl f Ns ).
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This is useful for adjusting rules by executing multiple
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.Nm
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commands in a script
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.Po
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e.g.,
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.Sq sh /etc/rc.firewall
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.Pc ,
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|
or by processing a file of many
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.Nm
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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. This causes the
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remote login session to be closed and the remainder of the ruleset is
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not processed. Access to the 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
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.Pq RST
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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
|
|
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 .
|
|
The search continues with the next rule. This feature is not yet implemented.
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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 ,
|
|
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 options IPFIREWALL_FORWARD.
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.It Ar skipto number
|
|
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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|
.It Ar uid user
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|
Match all TCP or UDP packets sent by or received for a
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.Ar user .
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|
A
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.Ar user
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may be matched by name or identification number.
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|
.It Ar gid group
|
|
Match all TCP or UDP packets sent by or received for a
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.Ar group .
|
|
A
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.Ar group
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may be matched by name or identification number.
|
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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.
|
|
.Pp
|
|
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
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.Ar log
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|
keyword a message will be printed on the console.
|
|
If the kernel was compiled with the
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.Dv IPFIREWALL_VERBOSE_LIMIT
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option, then by default logging will cease after the number
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of packets specified by the option are received for that
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particular chain entry. However, if
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.Ar logamount Ar number
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is used, that
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.Ar number
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|
will be the default logging limit rather than
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.Dv IPFIREWALL_VERBOSE_LIMIT .
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Logging may then be re-enabled by clearing the logging counter
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or 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 in the MIB base of
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.Dv net.inet.ip.fw .
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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.
|
|
.It Ar icmp
|
|
Only ICMP packets match.
|
|
.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).
|
|
.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>
|
|
.Op Ar ports
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|
.El
|
|
.Pp
|
|
The
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|
.Em <address/mask>
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|
may be specified as:
|
|
.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.
|
|
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.
|
|
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
|
|
An ipnumber with a mask width of the form 1.2.3.4:255.255.240.0.
|
|
In this case all ip numbers from 1.2.0.0 to 1.2.15.255 will match.
|
|
.El
|
|
.Pp
|
|
The sense of the match can be inverted by preceding an address with the
|
|
.Dq not
|
|
modifier, causing all other addresses to be matched instead. This
|
|
does not affect the selection of port numbers.
|
|
.Pp
|
|
With the TCP and UDP protocols, optional
|
|
.Em ports
|
|
may be specified as:
|
|
.Pp
|
|
.Bl -hang -offset flag
|
|
.It Ns {port|port-port} Ns Op ,port Ns Op ,...
|
|
.El
|
|
.Pp
|
|
Service names (from
|
|
.Pa /etc/services )
|
|
may be used instead of numeric port values.
|
|
A range may only be specified as the first value,
|
|
and the length of the port list is limited to
|
|
.Dv IP_FW_MAX_PORTS
|
|
(as defined in
|
|
.Pa /usr/src/sys/netinet/ip_fw.h )
|
|
ports.
|
|
A
|
|
.Ql \e
|
|
can be used to escape the
|
|
.Ql -
|
|
character in a service name:
|
|
.Pp
|
|
.Dl ipfw add count tcp from any ftp\e\e-data-ftp to any
|
|
.Pp
|
|
Fragmented packets which have a non-zero offset (i.e. not the first
|
|
fragment) will never match a rule which has one or more port
|
|
specifications. See the
|
|
.Ar frag
|
|
option for details on matching fragmented packets.
|
|
.Pp
|
|
Rules can apply to packets when they are incoming, or outgoing, or both.
|
|
The
|
|
.Ar in
|
|
keyword indicates the rule should only match incoming packets.
|
|
The
|
|
.Ar out
|
|
keyword indicates the rule should only match outgoing packets.
|
|
.Pp
|
|
To match packets going through a certain interface, specify
|
|
the interface using
|
|
.Ar via :
|
|
.Bl -hang -offset flag -width 1234567890123456
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|
.It Ar via ifX
|
|
Packet must be going through interface
|
|
.Ar ifX.
|
|
.It Ar via if*
|
|
Packet must be going through interface
|
|
.Ar ifX ,
|
|
where X is any unit number.
|
|
.It Ar via any
|
|
Packet must be going through
|
|
.Em some
|
|
interface.
|
|
.It Ar via ipno
|
|
Packet must be going through the interface having IP address
|
|
.Ar ipno .
|
|
.El
|
|
.Pp
|
|
The
|
|
.Ar via
|
|
keyword causes the interface to always be checked.
|
|
If
|
|
.Ar recv
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|
or
|
|
.Ar xmit
|
|
is used instead of
|
|
.Ar via ,
|
|
then the only receive or transmit interface (respectively) is checked.
|
|
By specifying both, it is possible to match packets based on both receive
|
|
and transmit interface, e.g.:
|
|
.Pp
|
|
.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) whenever
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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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Match 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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Match if this packet was on the way in.
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.It out
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Match if this packet was on the way out.
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.It ipoptions Ar spec
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Match 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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.Dq ! .
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.It established
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Match 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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Match 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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Match 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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.Dq ! .
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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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Match 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 KLD 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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kldload /modules/ipfw.ko && \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
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.Po
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see
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.Xr init 8
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for information on system security levels
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.Pc .
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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 add 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
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.Ar list
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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 ,
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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 init 8 ,
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.Xr kldload 8 ,
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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
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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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.Pp
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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
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Port aliases containing dashes cannot be first in a list.
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.Pp
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The
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.Dq tee
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action is unimplemented.
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.Sh AUTHORS
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.An Ugen J. S. Antsilevich ,
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.An Poul-Henning Kamp ,
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.An Alex Nash ,
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.An Archie Cobbs .
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API based upon code written by
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.An Daniel Boulet
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for BSDI.
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.Sh HISTORY
|
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.Nm Ipfw
|
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first appeared in
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.Fx 2.0 .
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