203 lines
8.6 KiB
Groff
203 lines
8.6 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. 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. 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. This rule
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normally causes all packets to be dropped. 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). In some cases
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(such as IP_FW_DEL), only the rule number is significant.
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.Sh COMMANDS
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The following socket options are used to manage the rule list:
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.Pp
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IP_FW_ADD inserts the rule into the rule list.
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.Pp
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IP_FW_DEL deletes all rules having the matching rule number.
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.Pp
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IP_FW_GET returns the (first) rule having the matching rule number.
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.Pp
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IP_FW_ZERO zeros the statistics associated with all rules having the
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matching rule number. If the rule number is zero, all rules are zeroed.
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.Pp
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IP_FW_FLUSH removes all rules (except 65535).
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.Pp
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When the kernel security level is greater than 2, only IP_FW_GET
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is allowed.
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.Sh RULE STRUCTURE
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Rules are described by the following structure:
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.Bd -literal
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/* Specify an interface */
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union ip_fw_if {
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struct in_addr fu_via_ip; /* Specified by IP address */
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struct { /* Specified by interface name */
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#define FW_IFNLEN 6 /* To keep structure on 2^x boundary */
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char name[FW_IFNLEN];
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short unit; /* -1 means match any unit */
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} fu_via_if;
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};
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/* One ipfw rule */
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struct ip_fw {
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u_long fw_pcnt,fw_bcnt; /* Packet and byte counters */
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struct in_addr fw_src, fw_dst; /* Source and destination IP addr */
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struct in_addr fw_smsk, fw_dmsk;/* Mask for src and dest IP addr */
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u_short fw_number; /* Rule number */
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u_short fw_flg; /* Flags word */
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#define IP_FW_MAX_PORTS 10 /* A reasonable maximum */
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u_short fw_pts[IP_FW_MAX_PORTS];/* Array of port numbers to match */
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u_char fw_ipopt,fw_ipnopt; /* IP options set/unset */
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u_char fw_tcpf,fw_tcpnf; /* TCP flags set/unset */
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#define IP_FW_ICMPTYPES_DIM (256 / (sizeof(unsigned) * 8))
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unsigned fw_icmptypes[IP_FW_ICMPTYPES_DIM]; /* ICMP types bitmap */
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long timestamp; /* timestamp (tv_sec) of last match */
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union ip_fw_if fw_in_if, fw_out_if;/* Incoming / outgoing interfaces */
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union {
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u_short fu_divert_port; /* Divert/tee port */
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u_short fu_skipto_rule; /* SKIPTO command rule number */
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u_short fu_reject_code; /* REJECT response code */
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} fw_un;
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u_char fw_prot; /* IP protocol */
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u_char fw_nports; /* N'of src ports and # of dst ports */
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/* in ports array (dst ports follow */
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/* src ports; max of 10 ports in all */
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/* count of 0 means match all ports) */
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};
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/* Encoding of number of source/dest ports from "fw_nports" */
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#define IP_FW_GETNSRCP(rule) ((rule)->fw_nports & 0x0f)
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#define IP_FW_SETNSRCP(rule, n) do { \\
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(rule)->fw_nports &= ~0x0f; \\
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(rule)->fw_nports |= (n); \\
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} while (0)
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#define IP_FW_GETNDSTP(rule) ((rule)->fw_nports >> 4)
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#define IP_FW_SETNDSTP(rule, n) do { \\
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(rule)->fw_nports &= ~0xf0; \\
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(rule)->fw_nports |= (n) << 4;\\
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} while (0)
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/* Flags values for "flags" field */
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#define IP_FW_F_IN 0x0001 /* Check inbound packets */
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#define IP_FW_F_OUT 0x0002 /* Check outbound packets */
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#define IP_FW_F_IIFACE 0x0004 /* Apply inbound interface test */
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#define IP_FW_F_OIFACE 0x0008 /* Apply outbound interface test */
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#define IP_FW_F_COMMAND 0x0070 /* Mask for type of chain entry: */
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#define IP_FW_F_DENY 0x0000 /* This is a deny rule */
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#define IP_FW_F_REJECT 0x0010 /* Deny and send a response packet */
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#define IP_FW_F_ACCEPT 0x0020 /* This is an accept rule */
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#define IP_FW_F_COUNT 0x0030 /* This is a count rule */
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#define IP_FW_F_DIVERT 0x0040 /* This is a divert rule */
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#define IP_FW_F_TEE 0x0050 /* This is a tee rule */
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#define IP_FW_F_SKIPTO 0x0060 /* This is a skipto rule */
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#define IP_FW_F_PRN 0x0080 /* Print if this rule matches */
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#define IP_FW_F_SRNG 0x0100 /* The first two src ports are a min *
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* and max range (stored in host byte *
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* order). */
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#define IP_FW_F_DRNG 0x0200 /* The first two dst ports are a min *
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* and max range (stored in host byte *
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* order). */
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#define IP_FW_F_IIFNAME 0x0400 /* In interface by name/unit (not IP) */
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#define IP_FW_F_OIFNAME 0x0800 /* Out interface by name/unit (not IP) */
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#define IP_FW_F_INVSRC 0x1000 /* Invert sense of src check */
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#define IP_FW_F_INVDST 0x2000 /* Invert sense of dst check */
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#define IP_FW_F_FRAG 0x4000 /* Fragment */
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#define IP_FW_F_ICMPBIT 0x8000 /* ICMP type bitmap is valid */
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#define IP_FW_F_MASK 0xFFFF /* All possible flag bits mask */
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.Ed
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.Sh 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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IP_FW_F_DENY - drop packet
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IP_FW_F_REJECT - drop packet; send rejection via ICMP or TCP
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IP_FW_F_ACCEPT - accept packet
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IP_FW_F_COUNT - increment counters; continue matching
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IP_FW_F_DIVERT - divert packet to a divert(4) socket
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IP_FW_F_TEE - copy packet to a divert(4) socket; continue
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IP_FW_F_SKIPTO - skip to rule number fu_skipto_rule
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.Pp
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In the case of IP_FW_F_REJECT, if the fu_reject_code 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 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 IP_FW_F_SKIPTO, all succeeding rules having rule number less
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than fu_skipto_rule are skipped.
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.Sh KERNEL OPTIONS
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Options in the kernel configuration file:
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IPFIREWALL - enable ipfirewall.
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IPFIREWALL_VERBOSE - enable firewall output
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IPFIREWALL_VERBOSE_LIMIT - limit firewall output
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IPDIVERT - enable divert(4) sockets.
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.Pp
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When packets match a rule with the IP_FW_F_PRN bit set, a message
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is logged to the console if IPFIREWALL_VERBOSE has been enabled;
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IPFIREWALL_VERBOSE_LIMIT limits the maximum number of times each
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rule can cause a log message. 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 DIAGNOSTICS
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[EINVAL] The IP option field was improperly formed; an option
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field was shorter than the minimum value or longer than
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the option buffer provided. A structural error in
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ip_fw structure occurred (n_src_p+n_dst_p too big,
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ports set for ALL/ICMP protocols etc.). An invalid
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rule number was used.
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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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The ``tee'' rule is not yet implemented (currently it has no effect).
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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 Daniel Boulet <danny@BouletFermat.ab.ca>.
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It has been heavily modified and ported to FreeBSD
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by Ugen J.S.Antsilevich <ugen@NetVision.net.il>.
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.Pp
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Several enhancements added by Archie Cobbs <archie@whistle.com>.
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