.\" $OpenBSD: pf.conf.5,v 1.92 2002/10/07 12:39:29 dhartmei Exp $ .\" .\" Copyright (c) 2002, Daniel Hartmeier .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" .\" - Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" - Redistributions in binary form must reproduce the above .\" copyright notice, this list of conditions and the following .\" disclaimer in the documentation and/or other materials provided .\" with the distribution. .\" .\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS .\" "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT .\" LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS .\" FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE .\" COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, .\" BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; .\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER .\" CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN .\" ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE .\" POSSIBILITY OF SUCH DAMAGE. .\" .Dd July 2, 2002 .Dt PF.CONF 5 .Os .Sh NAME .Nm pf.conf .Nd filtering and translation (NAT) rules file for the packet filter .Sh DESCRIPTION The .Xr pf 4 packet filter drops, passes and modifies packets according to the rules defined in this file. Filter rules are used to selectively pass traffic while translation rules specify which addresses are to be mapped and which are to be redirected. For each packet inspected by the filter, the set of rules is evaluated from top to bottom, and the last matching rule decides what action is performed. For each packet inspected by the translator, the set of rules is evaluated from top to bottom, and the first matching rule decides what action is performed. In short: filters are last match, nat is first match. Rules must be in order: options, scrub, nat, filter. .Sh FILTER RULES While filter rules are typically manipulated using .Xr pfctl 8 other utilities may be written using the .Xr ioctl 2 interface described in .Xr pf 4 . .Pp For each packet processed by the packet filter, the filter rules are evaluated in sequential order, from first to last. Each rule either matches the packet or doesn't. The last matching rule decides what action is taken. .Pp If no rule matches the packet, the default action is .Em pass . .Pp To block everything by default and only pass packets that match explicit rules, one uses .Bd -literal .Cm block in all .Cm block out all .Ed .Pp as the first two rules. .Pp For each packet processed by the translator, the translation rules are evaluated in sequential order, from first to last. Each rule either matches the packet or doesn't. The first matching rule decides what action is taken. .Pp If no rule matches the packet, the default action is to pass the packet up to the filter unmodified. It should be noted that all translations of packets occur before the filters are applied. Hence, rules for redirected packets should specify the address and port after translation. Note that all translation rules apply only to packets that pass through the specified interface. For instance, redirecting port 80 on an external interface to an internal web server will only work for connections originating from the outside. Connections to the address of the external interface from local hosts will not be redirected, since such packets do not actually pass through the external interface. Redirections can't reflect packets back through the interface they arrive on, they can only be redirected to hosts connected to different interfaces or to the firewall itself. .Sh OPTIONS .Ss timeout .Bl -tag -width interval -compact .It Em interval Interval between purging expired states and fragments. .It Em frag Seconds before an unassembled fragment is expired. .El .Pp When a packet matches a stateful connection, the seconds to live of the connection will be updated to that of the proto.modifier which corresponds to the connection state. Each packet which matches this state will reset the TTL. Tuning these values may improve the performance of the firewall at the risk of dropping valid idled connections. .Pp .Bl -tag -width "tcp.established " -compact .It Em tcp.first The state after the first packet. .It Em tcp.opening The state before the destination host ever sends a packet. .It Em tcp.established The fully established state. .It Em tcp.closing The state after the first FIN has been sent. .It Em tcp.finwait The state after both FINs have been exchanged and the connection is closed. Some hosts (notably web servers on Solaris) send TCP packets even after closing the connection. Increasing tcp.finwait (and possibly tcp.closing) can prevent blocking of such packets. .It Em tcp.closed The state after one endpoint sends a RST. .El .Pp ICMP and UDP are handled in a similar fashion to TCP but with a much more limited set of states: .Pp .Bl -tag -width "udp.multiple " -compact .It Em udp.first The state after the first packet. .It Em udp.single The state if the source host sends more than one packet but the destination host has never sent one back. .It Em udp.multiple The state if both hosts have sent packets. .It Em icmp.first The state after the first packet. .It Em icmp.error The state after an icmp error came back in response to an icmp packet. .El .Pp Other protocols are handled similarly to UDP: .Pp .Bl -tag -width "other.multiple " -compact .It Em other.first .It Em other.single .It Em other.multiple .El .Pp Example: .Bd -literal set timeout tcp.established 3600 set timeout { tcp.opening 30, tcp.closing 900 } .Ed .Ss loginterface Enable collection of packet and byte count statistics for the given interface. These statistics can be viewed using .Bd -literal # pfctl -s info .Ed .Pp In this example pf is told to collect statistics on the interface named dc0: .Bd -literal set loginterface dc0 .Ed .Pp One can unset the loginterface using .Bd -literal set loginterface none .Ed .Pp .Ss limit Sets hard limits on the memory pools used by the packet filter. See .Xr pool 9 for an explanation of memory pools. .Pp For example, .Bd -literal set limit states 20000 .Ed .Pp sets the maximum number of entries in the memory pool used by state table entries (generated by 'keep state' rules) to 20000. .Bd -literal set limit frags 20000 .Ed .Pp sets the maximum number of entries in the memory pool used for fragment reassembly (generated by 'scrub' rules) to 20000. .Pp These can be combined: .Bd -literal set limit { states 20000, frags 20000 } .Ed .Ss optimization Optimize the engine to one of the following network topographies or environments: .Bl -tag -width "O high-latency " -compact .It Em default A normal network environment. Suitable for almost all networks. .It Em normal Alias for .Em default .It Em high-latency A high-latency environment (such as a satellite connection) .It Em satellite Alias for .Em high-latency .It Em aggressive Aggressively expire connections when they are likely no longer valid. This can greatly reduce the memory usage of the firewall at the cost of dropping idle connections early. .It Em conservative Extremely conservative settings. Pains will be taken to avoid dropping legitimate connections at the expense of greater memory utilization (possibly much greater on a busy network) and slightly increased processor utilization. .El Example: .Bd -literal set optimization aggressive .Ed .Sh ACTIONS .Bl -tag -width Fl .It Em block The packet is blocked. Optionally, the filter can return a TCP RST or ICMP UNREACHABLE packet to the sender, where applicable. Returning ICMP packets can have an ICMP code set by number or name, TCP RST can have a TTL set. .It Em pass The packet is passed. .It Em scrub The packet is run through normalization/defragmentation. Scrub rules are not considered last matching rules. IPv6 packets are not defragmented. .It Em binat A .Em binat rule specifies a bidirectional mapping between an external IP address and an internal IP address. .It Em nat A .Em nat rule specifies that IP addresses are to be changed as the packet traverses the given interface. This technique allows a single IP address on the translating host to support network traffic for a larger range of machines on an "inside" network. Although in theory any IP address can be used on the inside, it is strongly recommended that one of the address ranges defined by RFC 1918 be used. These netblocks are: .Bd -literal 10.0.0.0 - 10.255.255.255 (all of net 10, i.e., 10/8) 172.16.0.0 - 172.31.255.255 (i.e., 172.16/12) 192.168.0.0 - 192.168.255.255 (i.e., 192.168/16) .Ed .It Em rdr The packet is redirected to another destination and possibly a different port. .Em rdr rules can optionally specify port ranges instead of single ports. \'rdr ... port 2000:2999 -> ... port 4000\' redirects ports 2000 to 2999 (including port 2000 and 2999) to the same port 4000. \'rdr ... port 2000:2999 -> ... port 4000:*\' redirects port 2000 to 4000, 2001 to 4001, ..., 2999 to 4999. .El .Sh PARAMETERS The rule parameters specify for what packets a rule applies. A packet always comes in on or goes out through one interface. Most parameters are optional. If a parameter is specified, the rule only applies to packets with matching attributes. Certain parameters can be expressed as lists, in which case .Em pfctl generates all needed rule combinations. .Ss in or out The rule applies to incoming or outgoing packets. Either .Em in or .Em out must be specified. To cover both directions, two rules are needed. .Ss log .Bl -tag -width Fl .It Em log In addition to the action specified, a log message is generated. .It Em log-all Used with .Sq keep state or .Sq modulate state rules. Not only the packet that creates state is logged, but all packets of the connection. .El .Pp The logged packets are sent to the .Em pflog0 interface. This interface is monitored by the .Xr pflogd 8 logging daemon which dumps the logged packets to the file .Em /var/log/pflog in .Xr pcap 3 binary format. .Ss quick If a packet matches a rule which has the .Sq quick option set, this rule is considered the last matching rule, and evaluation of subsequent rules is skipped. .Ss on The rule applies only to packets coming in on or going out through this particular interface. .Ss The rule applies only to packets of this address family. Supported values are inet and inet6. .Ss proto The rule applies only to packets of this protocol. Common protocols used here are tcp, udp, icmp and ipv6-icmp. .Ss from port to port The rule applies only to packets with the specified source and destination addresses/ports. .Pp Addresses can be specified in CIDR notation (matching netblocks), as symbolic host names or interface names, or as any of the following keywords: .Bl -tag -width no-route -compact .It Em any means any address; .It Em no-route means any address which is not currently routable. .El .Pp Host name resolution and interface to address translation are done at rule set load-time. When the address of an interface (or host name) changes (by DHCP or PPP, for instance), the rule set must be reloaded for the change to be reflected in the kernel. Interface names surrounded by parentheses cause an automatic update of the rule whenever the referenced interface changes its address. Reloading the rule set is not required in this case. .Pp Ports can be specified using these operators .Bd -literal = (equal), != (unequal), < (lesser), <= (lesser or equal), > (greater), >= (greater or equal), >< (range) and <> (except range). .Ed .Pp >< and <> are binary operators (they take two arguments), and the range doesn't include the limits, for instance: .Bl -tag -width Fl .It Em port 2000 >< 2004 means .Sq all ports > 2000 and < 2004 , hence ports 2001, 2002 and 2003. .It Em port 2000 <> 2004 means .Sq all ports < 2000 or > 2004 , hence ports 1-1999 and 2005-65535. .El .Pp The host and port specifications are optional, as the following examples show: .Bd -literal pass in all pass in from any to any pass in proto tcp from any port <= 1024 to any pass in proto tcp from any to any port 25 pass in proto tcp from 10.0.0.0/8 port > 1024 to ! 10.1.2.3 port != 22 .Ed .Ss user group The rule only applies to packets of sockets owned by the specified user and group. For outgoing connections initiated from the firewall, this is the user that opened the connection. For incoming connections to the firewall itself, this is the user that listens on the destination port. For forwarded connections, where the firewall isn't a connection endpoint, the user and group are .Em unknown . .Pp All packets, both outgoing and incoming, of one connection are associated with the same user and group. Only TCP and UDP packets can be associated with users, for other protocols these parameters are ignored. .Pp User and group refer to the effective (as opposed to the real) IDs, in case the socket is created by a setuid/setgid process. Note that user and group IDs are stored when a socket is created; when a process creates a listening socket as root (for instance, because it wants to bind to a privileged port) and subsequently sets another user ID (to drop privileges), the socket's uid remains root. .Pp User and group IDs can be specified as either numbers or names, the syntax is similar to the one for ports. The value .Em unknown matches packets of forwarded connections. .Em unknown can only be used with operators = and !=, other constructs like 'user >= unknown' are invalid. Forwarded packets with unknown user and group ID match only rules that explicitely compare against .Em unknown with operator = or !=, for instance 'user >= 0' does not match forwarded packets. The following example allows only selected users to open outgoing connections: .Bd -literal block out proto { tcp, udp } all pass out proto { tcp, udp } all user { < 1000, dhartmei } keep state .Ed .Ss flags | / | / The rule only applies to TCP packets that have the flags set out of set . Flags not specified in are ignored. If is not set, all flags are specified. The flags are: (F)IN, (S)YN, (R)ST, (P)USH, (A)CK, (U)RG, (E)CE, and C(W)R. .Bl -tag -width Fl .It Em flags S/S Flag SYN is set. The other flags are ignored. .It Em flags S/SA Of SYN and ACK, exactly SYN is set. SYN, SYN+PSH, SYN+RST match, but SYN+ACK, ACK and ACK+RST don't. This is more restrictive than the previous example. .It Em flags S If the second set is not specified, it defaults to FSRPAUEW. Hence, only packets with SYN set and all other flags unset match this rule. This is more restrictive than the previous example. .It Em flags /SFRA If the first set is not specified, it defaults to none. All of SYN, FIN, RST and ACK must be unset. .El .Ss icmp-type code and ipv6-icmp-type code The rule only applies to ICMP or ICMPv6 packets with the specified type and code. This parameter is only valid for rules that cover protocols icmp or ipv6-icmp. The protocol and the icmp type indicator (icmp-type or ipv6-icmp-type) must match. .Ss allow-opts By default, packets which contain IP options are blocked. When .Em allow-opts is specified for a .Em pass rule, packets that pass the filter based on that rule (last matching) do so even if they contain IP options. For packets that match state, the rule that initially created the state is used. The implicit .Em pass rule that is used when a packet doesn't match any rules does not allow IP options. .Ss label Adds a label (name) to the rule, which can be used to identify the rule. For instance, .Em pfctl -s labels shows per-rule statistics for rules that have labels. .Pp The following macros can be used in labels: .Pp .Bl -tag -width $srcaddr -compact -offset indent .It Em $srcaddr the source IP address. .It Em $dstaddr the destination IP address. .It Em $srcport the source port specification. .It Em $dstport the destination port specification. .It Em $proto the protocol name. .It Em $nr the rule number. .El .Pp Example: .Bd -literal ips = "{ 1.2.3.4, 1.2.3.5 }" pass in proto tcp from any to $ips port >1023 label "$dstaddr:$dstport" .Ed .Pp expands to .Bd -literal pass in proto tcp from any to 1.2.3.4 port >1023 label "1.2.3.4:>1023" pass in proto tcp from any to 1.2.3.5 port >1023 label "1.2.3.5:>1023" .Ed .Pp Note that evaluation takes place at parse time. .Sh NO The .Sq no option is to a NAT rule what the .Sq quick option is to a filter rule. This option causes matching packets to remain untranslated. .Sh ROUTING If a packet matches a rule with a route option set, the packet filter will route the packet according to the type of route option. When such a rule creates state, the route option is also applied to all packets matching the same connection. .Ss fastroute The .Em fastroute option does a normal route lookup to find the next hop for the packet. .Ss route-to The .Em route-to option routes the packet to the specified interface with an optional address for the next hop. When a .Em route-to rule creates state, only packets that pass in the same direction as the filter rule specifies will be routed in this way. Packets passing in the opposite direction (replies) are not affected and routed normally. .Ss reply-to The .Em reply-to option is similar to .Em route-to but routes packets that pass in the opposite direction (replies) to the specified interface. Opposite direction is only defined in context of a state entry, and .Em route-to is useful only in rules that create state. It can be used on systems with multiple external connections to route all outgoing packets of a connection through the interface the incoming connection arrived through (symmetric routing enforcement). .Ss dup-to The .Em dup-to option creates a duplicate of the packet and routes it like .Em route-to. The original packet gets routed as it normally would. .Sh MACROS .Em pfctl supports macro definition and expansion like: .Bd -literal ext_if = "kue0" pass out on $ext_if from any to any keep state pass in on $ext_if proto tcp from any to any port 25 keep state .Ed .Pp Macro names must start with a letter and may contain letters, digits and underscores. Macros are not expanded recursively. .Sh STATEFUL INSPECTION .Em pf is a stateful packet filter, which means it can track the state of a connection. Instead of passing all traffic to port 25, for instance, one can pass only the initial packet and keep state. .Pp If a packet matches a pass ... keep state rule, the filter creates a state for this connection and automatically lets pass all following packets of that connection. .Pp Before any rules are evaluated, the filter checks whether the packet matches any state. If it does, the packet is passed without evaluation of any rules. .Pp States are removed after the connection is closed or has timed out. .Pp This has several advantages. Comparing a packet to a state involves checking its sequence numbers. If the sequence numbers are outside the narrow windows of expected values, the packet is dropped. This prevents spoofing attacks, where the attacker sends packets with a fake source address/port but doesn't know the connection's sequence numbers. .Pp Also, looking up states is usually faster than evaluating rules. If one has 50 rules, all of them are evaluated sequentially in O(n). Even with 50000 states, only 16 comparisons are needed to match a state, since states are stored in a binary search tree that allows searches in O(log2 n). .Pp For instance: .Bd -literal block out all block in all pass out proto tcp from any to any flags S/SA keep state pass in proto tcp from any to any port 25 flags S/SA keep state .Ed .Pp This rule set blocks everything by default. Only outgoing connections and incoming connection to port 25 are allowed. The inital packet of each connection has the SYN flag set, will be passed and creates state. All further packets of these connections are passed if they match a state. .Pp Specifying flags S/SA restricts state creation to the initial SYN packet of the TCP handshake. One can also be less restrictive, and allow state creation from intermediate .Pq non-SYN packets. This will cause .Em pf to synchronize to existing connections, for instance if one flushes the state table. .Pp For UDP, which is stateless by nature, keep state will create state as well. UDP packets are matched to states using only host addresses and ports. .Pp ICMP messages fall in two categories: ICMP error messages, which always refer to a TCP or UDP packet, are matched against the refered to connection. If one keeps state on a TCP connection, and an ICMP source quench message referring to this TCP connection arrives, it will be matched to the right state and get passed. .Pp For ICMP queries, keep state creates an ICMP state, and .Em pf knows how to match ICMP replies to states. For example .Bd -literal pass out inet proto icmp all icmp-type echoreq keep state .Ed .Pp lets echo requests .Pq pings out, creates state, and matches incoming echo replies correctly to states. .Pp Note: nat/rdr rules implicitly create state for connections. .Sh STATE MODULATION Much of the security derived from TCP is attributable to how well the initial sequence numbers (ISNs) are chosen. Some popular stack implementations choose .Cm very poor ISNs and thus are normally susceptible to ISN prediction exploits. By applying a "modulate state" rule to a TCP connection, .Em pf will create a high quality random sequence number for each connection endpoint. .Pp The "modulate state" directive implicitly keeps state on the rule and is only applicable to TCP connections. .Pp For instance: .Bd -literal block out all block in all pass out proto tcp from any to any modulate state pass in proto tcp from any to any port 25 flags S/SA modulate state .Ed .Pp Caveat: If .Em pf picks up an already established connection .Po the firewall was rebooted, the state table was flushed, ... .Pc it will not be able to safely modulate the state of that connection. .Em pf will fall back and operate as if "keep state" was specified instead. Without this fallback, modulation would cause each host to think that the other end had somehow lost sync. .Pp Caveat: If the state table is flushed or the firewall is rebooted, currently modulated connections can not be continued or picked up again by the firewall. State modulation causes the firewall to phase shift the sequencing of each side of a connection .Po add a random number to each side. .Pc Both sides of the connection will notice, that its peer has suddenly shifted its sequence by a random amount. Neither side will be able to recover and the connection will stall and eventually close. .Sh STATE OPTIONS Both "keep state" and "modulate state" support the following options: .Bl -tag -width timeout_seconds -compact .It Em max number Limits the number of concurrent states the rule may create. When this limit is reached, further packets matching the rule that would create state are dropped, until existing states time out. .It Em timeout seconds Changes the timeout values used for states created by this rule. For a list of all valid timeout names, see .Xr pfctl 8 . .El .Pp Multiple options can be specified, separated by commas: .Bd -literal pass in proto tcp from any to any port www flags S/SA \\ keep state (max 100, tcp.established 60, tcp.closing 5) .Ed .Sh NORMALIZATION Packet normalization is invoked via the .Pa scrub directive. Normalization is used to sanitize packet content in such a way that there are no ambiguities in packet interpretation on the receiving side. .Pp The normalizer does IP fragment reassembly to prevent attacks that confuse intrusion detection systems by sending overlapping IP fragments. .Ss no-df Clears the .Pa dont-fragment bit from a matching ip packet. .Ss min-ttl Enforces a minimum ttl for matching ip packets. .Ss max-mss Enforces a maximum mss for matching tcp packets. .Pp Normalization occurs before filtering, scrub rules and pass/block rules are evaluated independently. Hence, their relative position in the rule set is not relevant, and packets can't be blocked before normalization. .Sh BLOCKING SPOOFED TRAFFIC "Spoofing" is the faking of IP addresses, typically for malicious purposes. The .Pa antispoof directive expands to a set of filter rules which will block all traffic with a source IP from the network(s) directly connected to the specified interface(s) from entering the system through any other interface. .Pp For example, the line .Bd -literal antispoof for lo0 .Ed .Pp expands to .Bd -literal block in on ! lo0 inet from 127.0.0.1/8 to any block in on ! lo0 inet6 from ::1 to any .Ed .Pp For non-loopback interfaces, there are additional rules to block incoming packets with a source IP address identical to the interface's IP(s). For example, assuming the interface wi0 had an IP address of 10.0.0.1 and a netmask of 255.255.255.0, the line .Bd -literal antispoof for wi0 inet .Ed .Pp expands to .Bd -literal block in on ! wi0 inet from 10.0.0.1/24 to any block in inet from 10.0.0.1 to any .Ed .Sh FRAGMENT HANDLING The size of IP datagrams (packets) can be significantly larger than the the maximum transmission unit (MTU) of the network. In cases when it is necessary or more effecient to send such large packets, the large packet will be fragmented into many smaller packets that will each fit onto the wire. Unfortunately for a firewalling device, only the first logical fragment will contain the necessary header information for the subprotocol that allows .Em pf to filter on things such as TCP ports or to perform NAT. .Pp There are four options for handling fragments in the packet filter: .Pp Using scrub rules, fragments can be reassembled by normalization. In this case, fragments are buffered until they form a complete packet, and only the completed packet is passed on to the filter. The advantage is that filter rules have to deal only with complete packets, and can ignore fragments. The drawback of caching fragments is the additional memory cost. But the full reassembly method is the only method that currently works with NAT. Full reassembly is triggered by the .Pa fragment reassemble modifier on a .Pa scrub rule. This is the default behavior of a .Pa scrub rule if no fragmentation modifier is supplied. .Pp Scrub also has two additional methods to track fragments without the high memory cost of full reassembly. The first is enabled via the .Pa fragment crop modifier. .Em pf will track the fragments and cache a small range descriptor. Duplicate fragments are dropped and overlaps are cropped. Thus data will only occur once on the wire with ambiguities resolving to the first occurance. Unlike the .Pa fragment reassemble modifier, fragments are not buffered, they are passed as soon as they are received. This reassembly mechanism does not yet work with NAT. .Pp Scrub's other method is the .Pa fragment drop-ovl modifier. It is almost identical to the .Pa fragment crop modifier except that all overlapping or duplicate fragments will be dropped and will cause the following corresponding fragments to be dropped as well. .Pp The alternative is to filter individual fragments with filter rules. If no scrub rule applies to a fragment, it is passed to the filter. Filter rules with matching IP header parameters decide whether the fragment is passed or blocked, in the same way as complete packets are filtered. Without reassembly, fragments can only be filtered based on IP header fields (source/destination address, protocol), since subprotocol header fields are not available (TCP/UDP port numbers, ICMP code/type). The .Pa fragment option can be used to restrict filter rules to apply only to fragments but not complete packets. Filter rules without the .Pa fragment option still apply to fragments, if they only specify IP header fields. For instance, the rule 'pass in proto tcp from any to any port 80' never applies to a fragment, even if the fragment is part of a TCP packet with destination port 80, because without reassembly, this information is not available for each fragment. This also means that fragments can't create new or match existing state table entries, which makes stateful filtering and address translations (NAT, redirection) for fragments impossible. .Pp It's also possible to reassemble only certain fragments by specifying source or destination addresses or protocols as parameters in scrub rules. .Pp In most cases, the benefits of reassembly outweigh the additional memory cost, and it's recommended to use scrub rules to reassemble all fragments via the .Pa fragment reassemble modifier. .Pp The memory allocated for fragment caching can be limited using .Xr pfctl 8 . Once this limit is reached, fragments that would have to be cached are dropped until other entries time out. The timeout value can also be adjusted. .Pp Currently, only IPv4 fragments are supported and IPv6 fragments are blocked unconditionally. .Sh FILTER EXAMPLES .Bd -literal # The external interface is kue0 # (157.161.48.183, the only routable address) # and the private network is 10.0.0.0/8, for which we are doing NAT. # use a macro for the interface name, so it can be changed easily ext_if = "kue0" # normalize all incoming traffic scrub in on $ext_if all fragment reassemble # block and log everything by default block out log on $ext_if all block in log on $ext_if all block return-rst out log on $ext_if proto tcp all block return-rst in log on $ext_if proto tcp all block return-icmp out log on $ext_if proto udp all block return-icmp in log on $ext_if proto udp all # block anything coming from source we have no back routes for block in from no-route to any # block and log outgoing packets that don't have our address as source, # they are either spoofed or something is misconfigured (NAT disabled, # for instance), we want to be nice and don't send out garbage. block out log quick on $ext_if from ! 157.161.48.183 to any # silently drop broadcasts (cable modem noise) block in quick on $ext_if from any to 255.255.255.255 # block and log incoming packets from reserved address space and invalid # addresses, they are either spoofed or misconfigured, we can't reply to # them anyway (hence, no return-rst). block in log quick on $ext_if from { 10.0.0.0/8, 172.16.0.0/12, \\ 192.168.0.0/16, 255.255.255.255/32 } to any # ICMP # pass out/in certain ICMP queries and keep state (ping) # state matching is done on host addresses and ICMP id (not type/code), # so replies (like 0/0 for 8/0) will match queries # ICMP error messages (which always refer to a TCP/UDP packet) are # handled by the TCP/UDP states pass out on $ext_if inet proto icmp all icmp-type 8 code 0 keep state pass in on $ext_if inet proto icmp all icmp-type 8 code 0 keep state # UDP # pass out all UDP connections and keep state pass out on $ext_if proto udp all keep state # pass in certain UDP connections and keep state (DNS) pass in on $ext_if proto udp from any to any port domain keep state # TCP # pass out all TCP connections and modulate state pass out on $ext_if proto tcp all modulate state # pass in certain TCP connections and keep state (SSH, SMTP, DNS, IDENT) pass in on $ext_if proto tcp from any to any port { ssh, smtp, domain, \\ auth } flags S/SA keep state # pass in data mode connections for ftp-proxy running on this host. # (see ftp-proxy(8) for details) pass in on $ext_if proto tcp from any to 157.161.48.183 port >= 49152 \\ flags S/SA keep state .Ed .Sh NAT EXAMPLES This example maps incoming requests on port 80 to port 8080, on which Apache Tomcat is running (say Tomcat is not run as root, therefore lacks permission to bind to port 80). .Bd -literal # map tomcat on 8080 to appear to be on 80 rdr on ne3 proto tcp from any to any port 80 -> 127.0.0.1 port 8080 .Ed .Pp In the example below, vlan12 is configured for the 192.168.168.1; the machine translates all packets coming from 192.168.168.0/24 to 204.92.77.111 when they are going out any interface except vlan12. This has the net effect of making traffic from the 192.168.168.0/24 network appear as though it is the Internet routeable address 204.92.77.111 to nodes behind any interface on the router except for the nodes on vlan12. (Thus, 192.168.168.1 can talk to the 192.168.168.0/24 nodes.) .Bd -literal nat on ! vlan12 from 192.168.168.0/24 to any -> 204.92.77.111 .Ed .Pp In the example below, fxp1 is the outside interface; the machine sits between a fake internal 144.19.74.* network, and a routable external IP of 204.92.77.100. The "no nat" rule excludes protocol AH from being translated. .Bd -literal #NO NAT no nat on fxp1 proto ah from 144.19.74.0/24 to any nat on fxp1 from 144.19.74.0/24 to any -> 204.92.77.100 .Ed .Pp In the example below, fxp0 is the internal interface. Packets bound for one specific server, as well as those generated by the sysadmins are not proxied, all other connections are. .Bd -literal # NO RDR no rdr on fxp0 from any to $server port 80 no rdr on fxp0 from $sysadmins to any port 80 rdr on fxp0 from any to any port 80 -> 127.0.0.1 port 80 .Ed .Pp This longer example uses both a NAT and a redirection. Interface kue0 is the outside interface, and its external address is 157.161.48.183. Interface fxp0 is the inside interface, and we are running .Xr ftp-proxy 8 listening for outbound ftp sessions captured to port 8081. .Bd -literal # NAT # translate outgoing packets' source addresses (any protocol) # in this case, any address but the gateway's external address is mapped nat on kue0 inet from ! (kue0) to any -> (kue0) # NAT PROXYING # map outgoing packets' source port to an assigned proxy port instead of # an arbitrary port # in this case, proxy outgoing isakmp with port 500 on the gateway nat on kue0 inet proto udp from any port = isakmp to any -> (kue0) \\ port 500 # BINAT # translate outgoing packets' source address (any protocol) # translate incoming packets' destination address to an internal machine # (bidirectional) binat on kue0 from 10.1.2.150 to any -> (kue0) # RDR # translate incoming packets' destination addresses # as an example, redirect a TCP and UDP port to an internal machine rdr on kue0 inet proto tcp from any to (kue0) port 8080 -> 10.1.2.151 \\ port 22 rdr on kue0 inet proto udp from any to (kue0) port 8080 -> 10.1.2.151 \\ port 53 # RDR # translate outgoing ftp control connections to send them to localhost # for proxying with ftp-proxy(8) running on port 8081 rdr on fxp0 proto tcp from any to any port 21 -> 127.0.0.1 port 8081 .Ed .Sh GRAMMAR Syntax for .Em pf.conf in BNF: .Bd -literal line = ( option | pf_rule | nat_rule | binat_rule | rdr_rule | antispoof_rule ) option = set ( [ "timeout" ( timeout | "{" timeout-list "}" ) ] | [ "optimization" [ "default" | "normal" | "high-latency" | "satellite" | "aggressive" | "conservative" ] ] [ "limit" ( limit | "{" limit-list "}" ) ] | [ "loginterface" ( interface-name | "none" ) ] ) . pf_rule = action ( "in" | "out" ) [ "log" | "log-all" ] [ "quick" ] [ "on" ifspec ] [ route ] [ af ] [ protospec ] hosts [ user ] [ group ] [ flags ] [ icmp-type | ipv6-icmp-type ] [ tos ] [ ( "keep" | "modulate" ) "state" [ "(" state-opts ")" ] ] [ "fragment" ] [ "no-df" ] [ "min-ttl" number ] [ "max-mss" number ] [ fragmentation ] [ "allow-opts" ] [ "label" string ] . nat_rule = [ "no" ] "nat" "on" ifspec [ af ] [ protospec ] hosts [ "->" address [ portspec ] ] . binat_rule = [ "no" ] "binat" "on" interface-name [ af ] [ "proto" ( proto-name | proto-number ) ] "from" address "to" ipspec [ "->" address ] . rdr_rule = [ "no" ] "rdr" "on" ifspec [ af ] [ protospec ] "from" ipspec "to" ipspec [ portspec ] [ "->" address [ portspec ] ] . antispoof_rule = "antispoof" [ "log" ] [ "quick" ] "for" ( interface-name | "{" interface-list "}" ) [ af ] . action = "pass" | "block" [ return ] | "scrub" . return = "return-rst" [ "(" "ttl" number ")" ] | "return-icmp" [ "(" ( icmp-code-name | icmp-code-number ) ")" ] | "return-icmp6" [ "(" ( icmp-code-name | icmp-code-number ) ")" ] . ifspec = ( [ "!" ] interface-name ) | "{" interface-list "}" interface-list = [ "!" ] interface-name [ [ "," ] interface-list ] . route = "fastroute" | "route-to" "(" interface-name address ")" | "route-to" interface-name | "reply-to" "(" interface-name address ")" | "reply-to" interface-name | "dup-to" "(" interface-name address ")" | "dup-to" interface-name af = "inet" | "inet6" . protospec = "proto" ( proto-name | proto-number | "{" proto-list "}" ) . proto-list = ( proto-name | proto-number ) [ [ "," ] proto-list ] . hosts = "all" | "from" ( "any" | "no-route" | "self" | host | "{" host-list "}" ) [ port ] "to" ( "any" | "no-route" | "self" | host | "{" host-list "}" ) [ port ] . ipspec = "any" | host | "{" host-list "}" . host = [ "!" ] address [ "/" mask-bits ] . address = ( interface-name | "(" interface-name ")" | host-name | ipv4-dotted-quad | ipv6-coloned-hex ) . host-list = host [ [ "," ] host-list ] . port = "port" ( unary-op | binary-op | "{" op-list "}" ) . portspec = "port" ( number | name ) [ ":" ( "*" | number | name ) ] . user = "user" ( unary-op | binary-op | "{" op-list "}" ) . group = "group" ( unary-op | binary-op | "{" op-list "}" ) . unary-op = [ "=" | "!=" | "<" | "<=" | ">" | ">=" ] ( name | number ) . binary-op = number ( "<>" | "><" ) number . op-list = ( unary-op | binary-op ) [ [ "," ] op-list ] . flags = "flags" ( flag-set | flag-set "/" flag-set | "/" flag-set ) . flag-set = [ "F" ] [ "S" ] [ "R" ] [ "P" ] [ "A" ] [ "U" ] [ "E" ] [ "W" ] . icmp-type = "icmp-type" ( icmp-type-code | "{" icmp-list "}" ) . ipv6-icmp-type = "ipv6-icmp-type" ( icmp-type-code | "{" icmp-list "}" ) . icmp-type-code = ( icmp-type-name | icmp-type-number ) [ "code" ( icmp-code-name | icmp-code-number ) ] . icmp-list = icmp-type-code [ [ "," ] icmp-list ] . tos = "tos" ( "lowdelay" | "throughput" | "reliability" | [ "0x" ] number ) . state-opts = state-opt [ [ "," ] state-opts ] . state-opt = ( "max" seconds ) | ( timeout seconds ) . fragmentation = [ "fragment reassemble" | "fragment crop" | "fragment drop-ovl" ] . timeout-list = timeout [ [ "," ] timeout-list ] . timeout = ( "tcp.first" | "tcp.opening" | "tcp.established" | "tcp.closing" | "tcp.finwait" | "tcp.closed" | "udp.first" | "udp.single" | "udp.multiple" | "icmp.first" | "icmp.error" | "other.first" | "other.multiple" ) seconds . seconds = number . limit-list = limit [ [ "," ] limit-list ] . limit = ( "states" | "frags" ) number . .Ed .Sh FILES .Bl -tag -width "/etc/pf.conf" -compact .It Pa /etc/hosts .It Pa /etc/pf.conf .It Pa /etc/protocols .It Pa /etc/services .El .Sh SEE ALSO .Xr pf 4 , .Xr hosts 5 , .Xr protocols 5 , .Xr services 5 , .Xr ftp-proxy 8 , .Xr pfctl 8 , .Xr pflogd 8 .Sh HISTORY The .Nm file format appeared in .Ox 3.0 .