IPF(5) | File Formats and Configurations | IPF(5) |
ipf, ipf.conf, ipf6.conf - IP packet filter rule syntax
A rule file for ipf may have any name or even be stdin. As ipfstat produces parsable rules as output when displaying the internal kernel filter lists, it is quite plausible to use its output to feed back into ipf. Thus, to remove all filters on input packets, the following could be done:
# ipfstat -i | ipf -rf -
The format used by ipf for construction of filtering rules can be described using the following grammar in BNF:
filter-rule = [ insert ] action in-out [ options ] [ tos ] [ ttl ] [ proto ] ip [ group ]. insert = "@" decnumber . action = block | "pass" | log | "count" | skip | auth | call . in-out = "in" | "out" . options = [ log ] [ tag ] [ "quick" ] [ "on" interface-name [ dup ]
[ froute ] [ replyto ] ] . tos = "tos" decnumber | "tos" hexnumber . ttl = "ttl" decnumber . proto = "proto" protocol . ip = srcdst [ flags ] [ with withopt ] [ icmp ] [ keep ] . group = [ "head" decnumber ] [ "group" decnumber ] . block = "block" [ return-icmp[return-code] | "return-rst" ] . log = "log" [ "body" ] [ "first" ] [ "or-block" ] [ "level" loglevel ] . tag = "tag" tagid . skip = "skip" decnumber . auth = "auth" | "preauth" . call = "call" [ "now" ] function-name . dup = "dup-to" interface-name [ ":" ipaddr ] . froute = "fastroute" | "to" interface-name [ ":" ipaddr ] . replyto = "reply-to" interface-name [ ":" ipaddr ] . protocol = "tcp/udp" | "udp" | "tcp" | "icmp" | decnumber . srcdst = "all" | fromto . fromto = "from" [ "!" ] object "to" [ "!" ] object . return-icmp = "return-icmp" | "return-icmp-as-dest" . return-code = "(" icmp-code ")" . object = addr [ port-comp | port-range ] . addr = "any" | nummask | host-name [ "mask" ipaddr | "mask" hexnumber ] . addr = "any" | "<thishost>" | nummask | host-name [ "mask" ipaddr | "mask" hexnumber ] . port-comp = "port" compare port-num . port-range = "port" port-num range port-num . flags = "flags" flag { flag } [ "/" flag { flag } ] . with = "with" | "and" . icmp = "icmp-type" icmp-type [ "code" decnumber ] . return-code = "(" icmp-code ")" . keep = "keep" "state" [ "(" state-options ")" ] | "keep" "frags" . loglevel = facility"."priority | priority . nummask = host-name [ "/" decnumber ] . host-name = ipaddr | hostname | "any" . ipaddr = host-num "." host-num "." host-num "." host-num . host-num = digit [ digit [ digit ] ] . port-num = service-name | decnumber . state-options = state-opts [ "," state-options ] . state-opts = "age" decnumber [ "/" decnumber ] | "strict" |
"no-icmp-err" | "limit" decnumber | "newisn" | "sync" . withopt = [ "not" | "no" ] opttype [ withopt ] . opttype = "ipopts" | "short" | "frag" | "opt" optname . optname = ipopts [ "," optname ] . ipopts = optlist | "sec-class" [ secname ] . secname = seclvl [ "," secname ] . seclvl = "unclass" | "confid" | "reserv-1" | "reserv-2" | "reserv-3" | "reserv-4" | "secret" | "topsecret" . icmp-type = "unreach" | "echo" | "echorep" | "squench" | "redir" | "timex" | "paramprob" | "timest" | "timestrep" | "inforeq" | "inforep" | "maskreq" | "maskrep" | decnumber . icmp-code = decumber | "net-unr" | "host-unr" | "proto-unr" | "port-unr" | "needfrag" | "srcfail" | "net-unk" | "host-unk" | "isolate" | "net-prohib" | "host-prohib" | "net-tos" | "host-tos" | "filter-prohib" | "host-preced" | "cutoff-preced" . optlist = "nop" | "rr" | "zsu" | "mtup" | "mtur" | "encode" | "ts" | "tr" | "sec" | "lsrr" | "e-sec" | "cipso" | "satid" | "ssrr" | "addext" | "visa" | "imitd" | "eip" | "finn" . facility = "kern" | "user" | "mail" | "daemon" | "auth" | "syslog" | "lpr" | "news" | "uucp" | "cron" | "ftp" | "authpriv" | "audit" | "logalert" | "local0" | "local1" | "local2" | "local3" | "local4" | "local5" | "local6" | "local7" . priority = "emerg" | "alert" | "crit" | "err" | "warn" | "notice" | "info" | "debug" . hexnumber = "0" "x" hexstring . hexstring = hexdigit [ hexstring ] . decnumber = digit [ decnumber ] . compare = "=" | "!=" | "<" | ">" | "<=" | ">=" | "eq" | "ne" | "lt" | "gt" | "le" | "ge" . range = "<>" | "><" . hexdigit = digit | "a" | "b" | "c" | "d" | "e" | "f" . digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" . flag = "F" | "S" | "R" | "P" | "A" | "U" .
This syntax is somewhat simplified for readability, some combinations that match this grammar are disallowed by the software because they do not make sense (such as tcp flags for non-TCP packets).
The "briefest" valid rules are (currently) no-ops and are of the form:
block in all
pass in all
log out all
count in all
Filter rules are checked in order, with the last matching rule determining the fate of the packet (but see the quick option, below).
Filters are installed by default at the end of the kernel's filter lists, prepending the rule with @n will cause it to be inserted as the n'th entry in the current list. This is especially useful when modifying and testing active filter rulesets. See ipf(8) for more information.
The action indicates what to do with the packet if it matches the rest of the filter rule. Each rule MUST have an action. The following actions are recognised:
block return-icmp(11) ...
Would return a Type-Of-Service (TOS) ICMP unreachable error.
The next word must be either in or out. Each packet moving through the kernel is either inbound (just been received on an interface, and moving towards the kernel's protocol processing) or outbound (transmitted or forwarded by the stack, and on its way to an interface). There is a requirement that each filter rule explicitly state which side of the I/O it is to be used on.
The list of options is brief, and all are indeed optional. Where options are used, they must be present in the order shown here. These are the currently supported options:
The keywords described in this section are used to describe attributes of the packet to be used when determining whether rules match or don't match. The following general-purpose attributes are provided for matching, and must be used in this order:
The from and to keywords are used to match against IP addresses (and optionally port numbers). Rules must specify BOTH source and destination parameters.
IP addresses may be specified in one of two ways: as a numerical address/mask, or as a hostname mask netmask. The hostname may either be a valid hostname, from either the hosts file or DNS (depending on your configuration and library) or of the dotted numeric form. There is no special designation for networks but network names are recognised. Note that having your filter rules depend on DNS results can introduce an avenue of attack, and is discouraged.
There is a special case for the hostname any which is taken to be 0.0.0.0/0 (see below for mask syntax) and matches all IP addresses. Only the presence of "any" has an implied mask, in all other situations, a hostname MUST be accompanied by a mask. It is possible to give "any" a hostmask, but in the context of this language, it is non-sensical.
The numerical format "x/y" indicates that a mask of y consecutive 1 bits set is generated, starting with the MSB, so a y value of 16 would give 0xffff0000. The symbolic "x mask y" indicates that the mask y is in dotted IP notation or a hexadecimal number of the form 0x12345678. Note that all the bits of the IP address indicated by the bitmask must match the address on the packet exactly; there isn't currently a way to invert the sense of the match, or to match ranges of IP addresses which do not express themselves easily as bitmasks (anthropomorphization; it's not just for breakfast anymore).
If a port match is included, for either or both of source and destination, then it is only applied to TCP and UDP packets. If there is no proto match parameter, packets from both protocols are compared. This is equivalent to "proto tcp/udp". When composing port comparisons, either the service name or an integer port number may be used. Port comparisons may be done in a number of forms, with a number of comparison operators, or port ranges may be specified. When the port appears as part of the from object, it matches the source port number, when it appears as part of the to object, it matches the destination port number. See the examples for more information.
The all keyword is essentially a synonym for "from any to any" with no other match parameters.
Following the source and destination matching parameters, the following additional parameters may be used:
F - FIN
S - SYN
R - RST
P - PUSH
A - ACK
U - URG
... flags S # becomes "flags S/AUPRFS" and will match # packets with ONLY the SYN flag set. ... flags SA # becomes "flags SA/AUPRFS" and will match any # packet with only the SYN and ACK flags set. ... flags S/SA # will match any packet with just the SYN flag set # out of the SYN-ACK pair; the common "establish" # keyword action. "S/SA" will NOT match a packet # with BOTH SYN and ACK set, but WILL match "SFP".
The second last parameter which can be set for a filter rule is whether or not to record historical information for that packet, and what sort to keep. The following information can be kept:
allowing packets which match these to flow straight through, rather than going through the access control list.
The last pair of parameters control filter rule "grouping". By default, all filter rules are placed in group 0 if no other group is specified. To add a rule to a non-default group, the group must first be started by creating a group head. If a packet matches a rule which is the head of a group, the filter processing then switches to the group, using that rule as the default for the group. If quick is used with a head rule, rule processing isn't stopped until it has returned from processing the group.
A rule may be both the head for a new group and a member of a non-default group (head and group may be used together in a rule).
When a packet is logged, with either the log action or option, the headers of the packet are written to the ipl packet logging pseudo-device. Immediately following the log keyword, the following qualifiers may be used (in order):
See ipl(5) for the format of records written to this device. The ipmon(8) program can be used to read and format this log.
The quick option is good for rules such as:
block in quick from any to any with ipopts
which will match any packet with a non-standard header length (IP options present) and abort further processing of later rules, recording a match and also that the packet should be blocked.
The "fall-through" rule parsing allows for effects such as this:
block in from any to any port < 6000
pass in from any to any port >= 6000
block in from any to any port > 6003
which sets up the range 6000-6003 as being permitted and all others being denied. Note that the effect of the first rule is overridden by subsequent rules. Another (easier) way to do the same is:
block in from any to any port 6000 <> 6003
pass in from any to any port 5999 >< 6004
Note that both the "block" and "pass" are needed here to effect a result as a failed match on the "block" action does not imply a pass, only that the rule hasn't taken effect. To then allow ports < 1024, a rule such as:
pass in quick from any to any port < 1024
would be needed before the first block. To create a new group for processing all inbound packets on le0/le1/lo0, with the default being to block all inbound packets, we would do something like:
block in all
block in quick on le0 all head 100
block in quick on le1 all head 200
block in quick on lo0 all head 300
and to then allow ICMP packets in on le0, only, we would do:
pass in proto icmp all group 100
Note that because only inbound packets on le0 are used processed by group 100, there is no need to respecify the interface name. Likewise, we could further breakup processing of TCP, etc, as follows:
block in proto tcp all head 110 group 100
pass in from any to any port = 23 group 110
and so on. The last line, if written without the groups would be:
pass in on le0 proto tcp from any to any port = telnet
Note, that if we wanted to say "port = telnet", "proto tcp" would need to be specified as the parser interprets each rule on its own and qualifies all service/port names with the protocol specified.
/dev/ipauth
/dev/ipl
/dev/ipstate
/etc/hosts
/etc/services
March 18, 2015 | OmniOS |