193 lines
4.9 KiB
Groff
193 lines
4.9 KiB
Groff
.\"
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.\" $FreeBSD$
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.\"
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.Dd June 22, 1997
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.Dt IPFIREWALL 4
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.Os
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.Sh NAME
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.Nm ipfirewall
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.Nd IP packet filter and traffic accounting
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.Sh SYNOPSIS
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.Fd #include <sys/types.h>
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.Fd #include <sys/queue.h>
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.Fd #include <netinet/in.h>
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.Fd #include <netinet/ip_fw.h>
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.Ft int
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.Fn setsockopt raw_socket IPPROTO_IP "ipfw option" "struct ipfw" size
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.Sh DESCRIPTION
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Ipfirewall (alias ipfw) is a system facility which allows filtering,
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redirecting, and other operations on IP packets travelling through
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system interfaces.
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Packets are matched by applying an ordered list
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of pattern rules against each packet until a match is found, at
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which point the corresponding action is taken.
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Rules are numbered
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from 1 to 65534; multiple rules may share the same number.
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.Pp
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There is one rule that always exists, rule number 65535.
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This rule
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normally causes all packets to be dropped.
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Hence, any packet which does not
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match a lower numbered rule will be dropped. However, a kernel compile
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time option
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.Dq IPFIREWALL_DEFAULT_TO_ACCEPT
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allows the administrator to change this fixed rule to permit everything.
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.Pp
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The value passed to
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.Fn setsockopt
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is a struct ip_fw describing the rule (see below).
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In some cases
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(such as
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.Dv IP_FW_DEL ) ,
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only the rule number is significant.
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.Ss Commands
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The following socket options are used to manage the rule list:
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.Bl -tag -width "IP_FW_FLUSH"
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.It Dv IP_FW_ADD
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inserts the rule into the rule list
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.It Dv IP_FW_DEL
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deletes all rules having the matching rule number
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.It Dv IP_FW_GET
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returns the (first) rule having the matching rule number
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.It Dv IP_FW_ZERO
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zeros the statistics associated with all rules having the
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matching rule number.
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If the rule number is zero, all rules are zeroed.
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.It Dv IP_FW_FLUSH
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removes all rules (except 65535).
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.El
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.Pp
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When the kernel security level is greater than 2, only
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.Dv IP_FW_GET
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is allowed.
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.Ss Rule Structure
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Rules are described by the structures in ip_fw.h.
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.Ss Rule Actions
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Each rule has an action described by the IP_FW_F_COMMAND bits in the
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flags word:
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.Bl -tag -width "IP_FW_F_DIVERT"
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.It Dv IP_FW_F_DENY
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Drop packet and stop processing.
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.It Dv IP_FW_F_REJECT
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drop packet; send rejection via ICMP or TCP and stop processing.
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.It Dv IP_FW_F_ACCEPT
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accept packet and stop processing.
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.It Dv IP_FW_F_COUNT
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increment counters; continue matching
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.It Dv IP_FW_F_DIVERT
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divert packet to a
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.Xr divert 4
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socket and stop processing.
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.It Dv IP_FW_F_TEE
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Send a copy of this packet to a
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.Xr divert 4
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socket and continue processing the original packet at the next rule.
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.It Dv IP_FW_F_SKIPTO
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skip to rule number
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.Va fu_skipto_rule
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At this time the target rule number must be greater than the active rule number.
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.It Dv IP_FW_F_PIPE
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The packet is marked for the use of
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.Xr dummynet 4 ,
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and processing stopped.
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.It Dv IP_FW_F_QUEUE
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The packet is marked for the use of
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.Xr dummynet 4 ,
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and processing stopped.
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.It Dv IP_FW_F_FWD
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The packet is accepted but the destination is hijacked. (see
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.Xr ipfw 8 )
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.El
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.Pp
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In the case of
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.Dv IP_FW_F_REJECT ,
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if the
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.Va fu_reject_code
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is a number
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from 0 to 255, then an ICMP unreachable packet is sent back to the
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original packet's source IP address, with the corresponding code.
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Otherwise, the value must be 256 and the protocol
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.Dv IPPROTO_TCP ,
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in which case a TCP reset packet is sent instead.
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.Pp
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With
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.Dv IP_FW_F_SKIPTO ,
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all succeeding rules having rule number less
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than
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.Va fu_skipto_rule
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are skipped.
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.Ss Kernel Options
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Options in the kernel configuration file:
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.Bl -tag -width "optionsXIPFIREWALL_VERBOSE_LIMIT"
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.It Cd options IPFIREWALL
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enable
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.Nm
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.It Cd options IPFIREWALL_VERBOSE
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enable firewall output
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.It Cd options IPFIREWALL_VERBOSE_LIMIT
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limit firewall output
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.It Cd options IPDIVERT
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enable
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.Xr divert 4
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sockets
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.El
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.Pp
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When packets match a rule with the
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.Dv IP_FW_F_PRN
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bit set, a message
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is logged to the console if
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.Dv IPFIREWALL_VERBOSE
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has been enabled;
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Dq IPFIREWALL_VERBOSE_LIMIT
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limits the maximum number of times each
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rule can cause a log message.
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These variables are also
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available via the
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.Xr sysctl 3
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interface.
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.Sh RETURN VALUES
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The
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.Fn setsockopt
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function returns 0 on success.
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Otherwise, -1 is returned and the global variable
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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The
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.Fn setsockopt
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function will fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The IP option field was improperly formed;
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an option field was shorter than the minimum value
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or longer than the option buffer provided.
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.It Bq Er EINVAL
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A structural error in ip_fw structure occurred
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(n_src_p+n_dst_p too big, ports set for ALL/ICMP protocols etc.).
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.It Bq Er EINVAL
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An invalid rule number was used.
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.El
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.Sh SEE ALSO
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.Xr setsockopt 2 ,
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.Xr divert 4 ,
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.Xr ip 4 ,
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.Xr ipfw 8 ,
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.Xr sysctl 8 .
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.Sh BUGS
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.Pp
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This man page still needs work.
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.Sh HISTORY
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The ipfw facility was initially written as package to BSDI
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by
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.An Daniel Boulet
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.Aq danny@BouletFermat.ab.ca .
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It has been heavily modified and ported to
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.Fx
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by
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.Ar Ugen J.S.Antsilevich
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.Aq ugen@NetVision.net.il .
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.Pp
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Several enhancements added by
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.An Archie Cobbs
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.Aq archie@FreeBSD.org .
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