Tom Eastep 2004-01-22 2001-2004 Thomas M. Eastep Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover, and with no Back-Cover Texts. A copy of the license is included in the section entitled GNU Free Documentation License. This documentation is intended primarily for reference. Step-by-step instructions for configuring Shorewall in common setups may be found in the QuickStart Guides.

Shorewall consists of the following components: params a parameter file installed in /etc/shorewall that can be used to establish the values of shell variables for use in other files. shorewall.conf a parameter file installed in /etc/shorewall that is used to set several firewall parameters. zones a parameter file installed in /etc/shorewall that defines a network partitioning into zones policy a parameter file installed in /etc/shorewall/ that establishes overall firewall policy. rules a parameter file installed in /etc/shorewall and used to express firewall rules that are exceptions to the high-level policies established in /etc/shorewall/policy. blacklist a parameter file installed in /etc/shorewall and used to list blacklisted IP/subnet/MAC addresses. ecn a parameter file installed in /etc/shorewall and used to selectively disable Explicit Congestion Notification (ECN - RFC 3168). functions a set of shell functions used by both the firewall and shorewall shell programs. Installed in /etc/shorewall prior to version 1.3.2, in /var/lib/shorewall in version s 1.3.2-1.3.8 and in /usr/lib/shorewall in later versions. modules a parameter file installed in /etc/shorewall and that specifies kernel modules and their parameters. Shorewall will automatically load the modules specified in this file. tos a parameter file installed in /etc/shorewall that is used to specify how the Type of Service (TOS) field in packets is to be set. common.def a parameter file installed in in /etc/shorewall that defines firewall-wide rules that are applied before a DROP or REJECT policy is applied. init.sh a shell script installed in /etc/init.d to automatically start Shorewall during boot. interfaces a parameter file installed in /etc/shorewall/ and used to describe the interfaces on the firewall system. hosts a parameter file installed in /etc/shorewall/ and used to describe individual hosts or subnetworks in zones. maclist a parameter file installed in /etc/shorewall and used to verify the MAC address (and possibly also the IP address(es)) of devices. masq This file also describes IP masquerading under Shorewall and is installed in /etc/shorewall. firewall a shell program that reads the configuration files in /etc/shorewall and configures your firewall. This file is installed in /usr/share/shorewall. nat a parameter file in /etc/shorewall used to define one-to-one NAT. proxyarp a parameter file in /etc/shorewall used to define Proxy Arp. rfc1918 a parameter file in /etc/shorewall used to define the treatment of packets under the norfc1918 interface option. routestopped a parameter file in /etc/shorewall used to define those hosts that can access the firewall when Shorewall is stopped. tcrules a parameter file in /etc/shorewall used to define rules for classifying packets for Traffic Shaping/Control. tunnels a parameter file in /etc/shorewall used to define IPSec tunnels. shorewall a shell program (requiring a Bourne shell or derivative) used to control and monitor the firewall. This should be placed in /sbin or in /usr/sbin (the install.sh script and the rpm install this file in /sbin). accounting a parameter file in /etc/shorewall used to define traffic accounting rules. This file was added in version 1.4.7. version a file created in /etc/shorewall/ (/var/lib/shorewall in version 1.3.2-1.3.8 and /usr/lib/shorewall beginning in version 1.3.9) that describes the version of Shorewall installed on your system. users and usersets files in /etc/shorewall allowing connections originating on the firewall to be policed by the user id and/or group id of the user. actions and action.template files in /etc/shorewall that allow you to define your own actions for rules in /etc/shorewall/rules.

You may use the file /etc/shorewall/params file to set shell variables that you can then use in some of the other configuration files. It is suggested that variable names begin with an upper case letter to distinguish them from variables used internally within the Shorewall programs NET_IF=eth0 NET_BCAST=130.252.100.255 NET_OPTIONS=blacklist,norfc1918 net $NET_IF $NET_BCAST $NET_OPTIONS The result will be the same as if the record had been written net eth0 130.252.100.255 blacklist,norfc1918 Variables may be used anywhere in the other configuration files.

This file is used to define the network zones. There is one entry in /etc/shorewall/zones for each zone; Columns in an entry are: ZONE short name for the zone. The name should be 5 characters or less in length (4 characters or less if you are running Shorewall 1.4.4 or later) and consist of lower-case letters or numbers. Short names must begin with a letter and the name assigned to the firewall is reserved for use by Shorewall itself. Note that the output produced by iptables is much easier to read if you select short names that are three characters or less in length. The name all may not be used as a zone name nor may the zone name assigned to the firewall itself via the FW variable in . DISPLAY The name of the zone as displayed during Shorewall startup. COMMENTS Any comments that you want to make about the zone. Shorewall ignores these comments. #ZONE DISPLAY COMMENTS net Net Internet loc Local Local networks dmz DMZ Demilitarized zone You may add, delete and modify entries in the /etc/shorewall/zones file as desired so long as you have at least one zone defined. If you rename or delete a zone, you should perform shorewall stop; shorewall start to install the change rather than shorewall restart. The order of entries in the /etc/shorewall/zones file is significant in some cases.

This file is used to tell the firewall which of your firewall's network interfaces are connected to which zone. There will be one entry in /etc/shorewall/interfaces for each of your interfaces. Columns in an entry are: ZONE A zone defined in the file or -. If you specify -, you must use the file to define the zones accessed via this interface. INTERFACE the name of the interface (examples: eth0, ppp0, ipsec+). Each interface can be listed on only one record in this file. DO NOT INCLUDE THE LOOPBACK INTERFACE (lo) IN THIS FILE!!! BROADCAST the broadcast address(es) for the sub-network(s) attached to the interface. This should be left empty for P-T-P interfaces (ppp*, ippp*); if you need to specify options for such an interface, enter - in this column. If you supply the special value detect in this column, the firewall will automatically determine the broadcast address. In order to use detect: the interface must be up before you start your firewall the interface must only be attached to a single sub-network (i.e., there must have a single broadcast address). OPTIONS a comma-separated list of options. Possible options include: arp_filter (Added in version 1.4.7) - This option causes /proc/sys/net/ipv4/conf/<interface>/arp_filter to be set with the result that this interface will only answer ARP who-has requests from hosts that are routed out of that interface. Setting this option facilitates testing of your firewall where multiple firewall interfaces are connected to the same HUB/Switch (all interface connected to the single HUB/Switch should have this option specified). Note that using such a configuration in a production environment is strongly recommended against. newnotsyn (Added in version 1.4.6) - This option overrides NEWNOTSYN=No for packets arriving on this interface. In other words, packets coming in on this interface are processed as if NEWNOTSYN=Yes had been specified in . routeback (Added in version 1.4.2) - This option causes Shorewall to set up handling for routing packets that arrive on this interface back out the same interface. If this option is specified, the ZONE column may not contain -. tcpflags (added in version 1.3.11) - This option causes Shorewall to make sanity checks on the header flags in TCP packets arriving on this interface. Checks include Null flags, SYN+FIN, SYN+RST and FIN+URG+PSH; these flag combinations are typically used for silent port scans. Packets failing these checks are logged according to the TCP_FLAGS_LOG_LEVEL option in and are disposed of according to the TCP_FLAGS_DISPOSITION option. blacklist This option causes incoming packets on this interface to be checked against the blacklist. dhcp The interface is assigned an IP address via DHCP or is used by a DHCP server running on the firewall. The firewall will be configured to allow DHCP traffic to and from the interface even when the firewall is stopped. You may also wish to use this option if you have a static IP but you are on a LAN segment that has a lot of Laptops that use DHCP and you select the norfc1918 option (see below). norfc1918 Packets arriving on this interface and that have a source address that is reserved in RFC 1918 or in other RFCs will be dropped after being optionally logged. If packet mangling is enabled in /etc/shorewall/shorewall.conf , then packets arriving on this interface that have a destination address that is reserved by one of these RFCs will also be logged and dropped. Addresses blocked by the standard rfc1918 file include those addresses reserved by RFC1918 plus other ranges reserved by the IANA or by other RFCs. Beware that as IPv4 addresses become in increasingly short supply, ISPs are beginning to use RFC 1918 addresses within their own infrastructure. Also, many cable and DSL modems have an RFC 1918 address that can be used through a web browser for management and monitoring functions. If you want to specify norfc1918 on your external interface but need to allow access to certain addresses from the above list, see FAQ 14. routefilter Invoke the Kernel's route filtering (anti-spoofing) facility on this interface. The kernel will reject any packets incoming on this interface that have a source address that would be routed outbound through another interface on the firewall. If you specify this option for an interface then the interface must be up prior to starting the firewall. dropunclean Packets from this interface that are selected by the unclean match target in iptables will be optionally logged and then dropped. This feature requires that UNCLEAN match support be configured in your kernel, either in the kernel itself or as a module. UNCLEAN support is broken in some versions of the kernel but appears to work ok in 2.4.17-rc1. Update 12/17/2001: The unclean match patch from 2.4.17-rc1 is available for download. I am currently running this patch applied to kernel 2.4.16. Update 12/20/2001: I've seen a number of tcp connection requests with OPT (020405B40000080A...) being dropped in the badpkt chain. This appears to be a bug in the remote TCP stack whereby it is 8-byte aligning a timestamp (TCP option 8) but rather than padding with 0x01 it is padding with 0x00. It's a tough call whether to deny people access to your servers because of this rather minor bug in their networking software. If you wish to disable the check that causes these connections to be dropped, here's a kernel patch against 2.4.17-rc2. logunclean This option works like dropunclean with the exception that packets selected by the unclean match target in iptables are logged but not dropped. The level at which the packets are logged is determined by the setting of LOGUNCLEAN and if LOGUNCLEAN has not been set, info is assumed. proxyarp (Added in version 1.3.5) - This option causes Shorewall to set /proc/sys/net/ipv4/conf/<interface>/proxy_arp and is used when implementing Proxy ARP Sub-netting as described at http://www.tldp.org/HOWTO/mini/Proxy-ARP-Subnet/. Do not set this option if you are implementing Proxy ARP through entries in . maclist (Added in version 1.3.10) - If this option is specified, all connection requests from this interface are subject to MAC Verification. May only be specified for ethernet interfaces. detectnets (Added in version 1.4.10) - If this option is specified, the zone named in the ZONE column will contain only the hosts routed through the interface named in the INTERFACE column. Do not set this option on your external (Internet) interface! The interface must be in the UP state when Shorewall is [re]started. My recommendations concerning options: External Interface -- tcpflags,blacklist,norfc1918,routefilter Wireless Interface -- maclist,routefilter,tcpflags,detectnets Don't use dropunclean -- It's broken in my opinion Use logunclean only when you are trying to debug a problem Use dhcp and proxyarp when needed. #ZONE INTERFACE BROADCAST OPTIONS net eth0 detect dhcp,norfc1918,blacklist #ZONE INTERFACE BROADCAST OPTIONS net ppp0 #ZONE INTERFACE BROADCAST OPTIONS loc eth1 192.168.1.255,192.168.12.255

For most applications, specifying zones entirely in terms of network interfaces is sufficient. There may be times though where you need to define a zone to be a more general collection of hosts. This is the purpose of the /etc/shorewall/hosts file. The only times that you need entries in /etc/shorewall/hosts are: You have more than one zone connecting through a single interface; or You have a zone that has multiple subnetworks that connect through a single interface and you want the Shorewall box to route traffic between those subnetworks. IF YOU DON'T HAVE EITHER OF THOSE SITUATIONS THEN DON'T TOUCH THIS FILE!! Columns in this file are: ZONE A zone defined in the file. HOST(S) The name of a network interface followed by a colon (:) followed by a comma-separated list either: An IP address (example - eth1:192.168.1.3) A subnet in CIDR notation (example - eth2:192.168.2.0/24) The interface name much match an entry in /etc/shorewall/interfaces. If you are running a version of Shorewall earlier than 1.4.6, only a single host/subnet address may be specified in an entry in /etc/shorewall/hosts. OPTIONS A comma-separated list of option routeback (Added in version 1.4.2) - This option causes Shorewall to set up handling for routing packets sent by this host group back back to the same group. maclist Added in version 1.3.10. If specified, connection requests from the hosts specified in this entry are subject to MAC Verification. This option is only valid for ethernet interfaces. If you don't define any hosts for a zone, the hosts in the zone default to i0:0.0.0.0/0 , i1:0.0.0.0/0, ... where i0, i1, ... are the interfaces to the zone. You probably DON'T want to specify any hosts for your internet zone since the hosts that you specify will be the only ones that you will be able to access without adding additional rules. 192.168.1.0/25 192.168.1.128/25 Your /etc/shorewall/interfaces file might look like: #ZONE INTERFACE BROADCAST OPTIONS net eth0 detect dhcp,norfc1918 - eth1 192.168.1.127,192.168.1.255 The - in the ZONE column for eth1 tells Shorewall that eth1 interfaces to multiple zones. #ZONE HOST(S) OPTIONS loc1 eth1:192.168.1.0/25 loc2 eth1:192.168.1.128/25 Your /etc/shorewall/interfaces file might look like: #ZONE INTERFACE BROADCAST OPTIONS net eth0 detect dhcp,norfc1918 - eth1 192.168.1.255,192.168.12.255 Your /etc/shorewall/hosts file might look like: #ZONE HOST(S) OPTIONS loc eth1:192.168.1.0/24 loc eth1:192.168.12.0/24 If you are running Shorewall 1.4.6 or later, your hosts file may look like: #ZONE HOST(S) OPTIONS loc eth1:192.168.1.0/24,192.168.12.0/24

The /etc/shorewall/interfaces and /etc/shorewall/hosts file allow you to define nested or overlapping zones. Such overlapping/nested zones are allowed and Shorewall processes zones in the order that they appear in the /etc/shorewall/zones file. So if you have nested zones, you want the sub-zone to appear before the super-zone and in the case of overlapping zones, the rules that will apply to hosts that belong to both zones is determined by which zone appears first in /etc/shorewall/zones. Hosts that belong to more than one zone may be managed by the rules of all of those zones. This is done through use of the special CONTINUE policy described below.

This file is used to describe the firewall policy regarding establishment of connections. Connection establishment is described in terms of clients who initiate connections and servers who receive those connection requests. Policies defined in /etc/shorewall/policy describe which zones are allowed to establish connections with other zones. Policies established in /etc/shorewall/policy can be viewed as default policies. If no rule in /etc/shorewall/rules applies to a particular connection request then the policy from /etc/shorewall/policy is applied. Five policies are defined: ACCEPT The connection is allowed. DROP The connection request is ignored. REJECT The connection request is rejected with an RST (TCP) or an ICMP destination-unreachable packet being returned to the client. CONTINUE The connection is neither ACCEPTed, DROPped nor REJECTed. CONTINUE may be used when one or both of the zones named in the entry are sub-zones of or intersect with another zone. For more information, see below. NONE (Added in version 1.4.1) - Shorewall should not set up any infrastructure for handling traffic from the SOURCE zone to the DEST zone. When this policy is specified, the LOG LEVEL and BURST:LIMIT columns must be left blank. For each policy specified in /etc/shorewall/policy, you can indicate that you want a message sent to your system log each time that the policy is applied. Entries in /etc/shorewall/policy have four columns as follows: SOURCE The name of a client zone (a zone defined in the file , the name of the firewall zone or all). DEST The name of a destination zone (a zone defined in the file , the name of the firewall zone or all). Shorewall automatically allows all traffic from the firewall to itself so the name of the firewall zone cannot appear in both the SOURCE and DEST columns. POLICY The default policy for connection requests from the SOURCE zone to the DESTINATION zone. LOG LEVEL Optional. If left empty, no log message is generated when the policy is applied. Otherwise, this column should contain an integer or name indicating a syslog level. LIMIT:BURST - optional If left empty, TCP connection requests from the SOURCE zone to the DEST zone will not be rate-limited. Otherwise, this column specifies the maximum rate at which TCP connection requests will be accepted followed by a colon (:) followed by the maximum burst size that will be tolerated. Example: 10/sec:40 specifies that the maximum rate of TCP connection requests allowed will be 10 per second and a burst of 40 connections will be tolerated. Connection requests in excess of these limits will be dropped. See the rules file documentation for an explaination of how rate limiting works. In the SOURCE and DEST columns, you can enter all to indicate all zones. The default /etc/shorewall/policy file is as follows. #SOURCE DEST POLICY LOG LEVEL LIMIT:BURST loc net ACCEPT net all DROP info all all REJECT info This table may be interpreted as follows: All connection requests from the local network to hosts on the internet are accepted. All connection requests originating from the internet are ignored and logged at level KERNEL.INFO. All other connection requests are rejected and logged. The firewall script processes the /etc/shorewall/policy file from top to bottom and uses the first applicable policy that it finds. For example, in the following policy file, the policy for (loc, loc) connections would be ACCEPT as specified in the first entry even though the third entry in the file specifies REJECT. #SOURCE DEST POLICY LOG LEVEL LIMIT:BURST loc all ACCEPT net all DROP info loc loc REJECT info

Shorewall allows a zone to be associated with more than one interface or with multiple networks that interface through a single interface. Beginning with Shorewall 1.4.1, Shorewall will ACCEPT all traffic from a zone to itself provided that there is no explicit policy governing traffic from that zone to itself (an explicit policy does not specify all in either the SOURCE or DEST column) and that there are no rules concerning connections from that zone to itself. If there is an explicit policy or if there are one or more rules, then traffic within the zone is handled just like traffic between zones is. Any time that you have multiple interfaces associated with a single zone, you should ask yourself if you really want traffic routed between those interfaces. Cases where you might not want that behavior are: Multiple net interfaces to different ISPs. You don't want to route traffic from one ISP to the other through your firewall. Multiple VPN clients. You don't necessarily want them to all be able to communicate between themselves using your gateway/router.

Where zones are nested or overlapping, the CONTINUE policy allows hosts that are within multiple zones to be managed under the rules of all of these zones. Let's look at an example: /etc/shorewall/zones: #ZONE DISPLAY COMMENTS sam Sam Sam's system at home net Internet The Internet loc Local Local Network /etc/shorewall/interfaces: #ZONE INTERFACE BROADCAST OPTIONS - eth0 detect dhcp,norfc1918 loc eth1 detect /etc/shorewall/hosts: #ZONE HOST(S) OPTIONS net eth0:0.0.0.0/0 sam eth0:206.191.149.197 Sam's home system is a member of both the sam zone and the net zone and as described above , that means that sam must be listed before net in /etc/shorewall/zones. /etc/shorewall/policy: #SOURCE DEST POLICY LOG LEVEL loc net ACCEPT sam all CONTINUE net all DROP info all all REJECT info The second entry above says that when Sam is the client, connection requests should first be process under rules where the source zone is sam and if there is no match then the connection request should be treated under rules where the source zone is net. It is important that this policy be listed BEFORE the next policy (net to all). Partial /etc/shorewall/rules: #ACTION SOURCE DEST PROTO DEST PORT(S) ... DNAT sam loc:192.168.1.3 tcp ssh DNAT net loc:192.168.1.5 tcp www ... Given these two rules, Sam can connect to the firewall's internet interface with ssh and the connection request will be forwarded to 192.168.1.3. Like all hosts in the net zone, Sam can connect to the firewall's internet interface on TCP port 80 and the connection request will be forwarded to 192.168.1.5. The order of the rules is not significant. Sometimes it is necessary to suppress port forwarding for a sub-zone. For example, suppose that all hosts can SSH to the firewall and be forwarded to 192.168.1.5 EXCEPT Sam. When Sam connects to the firewall's external IP, he should be connected to the firewall itself. Because of the way that Netfilter is constructed, this requires two rules as follows: #ACTION SOURCE DEST PROTO DEST PORT(S) ... DNAT sam fw tcp ssh DNAT net loc:192.168.1.3 tcp ssh ... The first rule allows Sam SSH access to the firewall. The second rule says that any clients from the net zone with the exception of those in the sam zone should have their connection port forwarded to 192.168.1.3. If you need to exclude more than one zone in this way, you can list the zones separated by commas (e.g., net!sam,joe,fred). This technique also may be used when the ACTION is REDIRECT.

The /etc/shorewall/rules file defines exceptions to the policies established in the /etc/shorewall/policy file. There is one entry in /etc/shorewall/rules for each of these rules. Shorewall automatically enables firewall->firewall traffic over the loopback interface (lo) -- that traffic cannot be regulated using rules and any rule that tries to regulate such traffic will generate a warning and will be ignored. Entries in the file have the following columns: ACTION ACCEPT, DROP, REJECT, CONTINUE These have the same meaning here as in the policy file above. DNAT Causes the connection request to be forwarded to the system specified in the DEST column (port forwarding). DNAT stands for Destination Network Address Translation DNAT- The above ACTION (DNAT) generates two iptables rules: a header-rewriting rule in the Netfilter nat table an ACCEPT rule in the Netfilter filter table. DNAT- works like DNAT but only generates the header-rewriting rule. REDIRECT Causes the connection request to be redirected to a port on the local (firewall) system. REDIRECT- The above ACTION (REDIRECT) generates two iptables rules: a header-rewriting rule in the Netfilter nat table an ACCEPT rule in the Netfilter filter table. REDIRECT- works like REDIRECT but only generates the header-rewriting rule. LOG Log the packet -- requires a syslog level (see below). QUEUE Forward the packet to a user-space application. This facility is provided to allow interfacing to ftwall for Kazaa filtering. When the protocol specified in the PROTO column is TCP (tcp, TCP or 6), Shorewall will only pass connection requests (SYN packets) to user space. This is for compatibility with ftwall. <user-defined action> (Shorewall 1.4.9 and later) Beginning with Shorewall version 1.4.7, you may rate-limit the rule by optionally following ACCEPT, DNAT[-], REDIRECT[-] or LOG with < <rate>/<interval>[:<burst>] > where <rate> is the number of connections per <interval> (sec or min) and <burst> is the largest burst permitted. If no burst value is given, a value of 5 is assumed. There may be no whitespace embedded in the specification. ACCEPT<2/sec:4> net dmz tcp 80 The first time this rule is reached, the packet will be accepted; in fact, since the burst is 4, the first four packets will be accepted. After this, it will be 500ms (1 second divided by the rate of 2) before a packet will be accepted from this rule, regardless of how many packets reach it. Also, every 500ms which passes without matching a packet, one of the bursts will be regained; if no packets hit the rule for 2 second, the burst will be fully recharged; back where we started. When rate limiting is specified on a rule with all in the SOURCE or DEST fields below, the limit will apply to each pair of zones individually rather than as a single limit for all pairs of zones covered by the rule. Rate limiting may also be specified in the RATE LIMIT column below; in that case, it must not be specified as part of the ACTION column. The ACTION (and rate limit) may optionally be followed by : and a syslog level (example: REJECT:info or ACCEPT<2/sec:4>:debugging). This causes the packet to be logged at the specified level prior to being processed according to the specified ACTION. Note: if the ACTION is LOG then you MUST specify a syslog level. The use of DNAT or REDIRECT requires that you have NAT enabled. SOURCE Describes the source hosts to which the rule applies.. The contents of this field must begin with the name of a zone defined in /etc/shorewall/zones, $FW or all. If the ACTION is DNAT or REDIRECT, sub-zones may be excluded from the rule by following the initial zone name with ! and a comma-separated list of those sub-zones to be excluded. There is an example above. If the source is not all then the source may be further restricted by adding a colon (:) followed by a comma-separated list of qualifiers. Qualifiers are may include: interface name refers to any connection requests arriving on the specified interface (example loc:eth4). Beginning with Shorwall 1.3.9, the interface name may optionally be followed by a colon (:) and an IP address or subnet (examples: loc:eth4:192.168.4.22, net:eth0:192.0.2.0/24). IP address refers to a connection request from the host with the specified address (example net:155.186.235.151). If the ACTION is DNAT, this must not be a DNS name. MAC Address in Shorewall format. subnet refers to a connection request from any host in the specified subnet (example net:155.186.235.0/24). DEST Describes the destination host(s) to which the rule applies. May take most of the forms described above for SOURCE plus the following two additional forms: An IP address followed by a colon and the port number that the server is listening on (service names from /etc/services are not allowed - example loc:192.168.1.3:80). A single port number (again, service names are not allowed) -- this form is only allowed if the ACTION is REDIRECT and refers to a server running on the firewall itself and listening on the specified port. Restrictions: MAC addresses may not be specified. In DNAT rules, only IP addresses may be given -- DNS names are not permitted. You may not specify both an IP address and an interface name in the DEST column. Unlike in the SOURCE column, a range of IP addresses may be specified in the DEST column as <first address>-<last address>. When the ACTION is DNAT or DNAT-, connections will be assigned to the addresses in the range in a round-robin fashion (load-balancing). This feature is available with DNAT rules only with Shorewall 1.4.6 and later versions; it is available with DNAT- rules in all versions that support DNAT-. PROTO Protocol. Must be a protocol name from /etc/protocols, a number or all. Specifies the protocol of the connection request. DEST PORT(S) Port or port range (<low port>:<high port>) being connected to. May only be specified if the protocol is tcp, udp or icmp. For icmp, this column's contents are interpreted as an icmp type. If you don't want to specify DEST PORT(S) but need to include information in one of the columns to the right, enter - in this column. You may give a list of ports and/or port ranges separated by commas. Port numbers may be either integers or service names from /etc/services. SOURCE PORTS(S) May be used to restrict the rule to a particular client port or port range (a port range is specified as <low port number>:<high port number>). If you don't want to restrict client ports but want to specify something in the next column, enter - in this column. If you wish to specify a list of port number or ranges, separate the list elements with commas (with no embedded white space). Port numbers may be either integers or service names from /etc/services. ORIGINAL DEST This column may only be non-empty if the ACTION is DNAT or REDIRECT. If DNAT or REDIRECT is the ACTION and the ORIGINAL DEST column is left empty, any connection request arriving at the firewall from the SOURCE that matches the rule will be forwarded or redirected. This works fine for connection requests arriving from the internet where the firewall has only a single external IP address. When the firewall has multiple external IP addresses or when the SOURCE is other than the internet, there will usually be a desire for the rule to only apply to those connection requests directed to particular IP addresses (see Example 2 below for another usage). Those IP addresses are specified in the ORIGINAL DEST column as a comma-separated list. The IP address(es) may be optionally followed by : and a second IP address. This latter address, if present, is used as the source address for packets forwarded to the server (This is called Source NAT or SNAT. If this list begins with ! then the rule will only apply if the original destination address matches none of the addresses listed. When using SNAT, it is a good idea to qualify the source with an IP address or subnet. Otherwise, it is likely that SNAT will occur on connections other than those described in the rule. The reason for this is that SNAT occurs in the Netfilter POSTROUTING hook where it is not possible to restrict the scope of a rule by incoming interface. #ACTION SOURCE DEST PROTO DEST SOURCE ORIGINAL # PORT(S) PORT(S) DEST DNAT loc:192.168.1.0/24 loc:192.168.1.3 tcp www - 206.124.146.179:192.168.1.3 If SNAT is not used (no : and second IP address), the original source address is used. If you want any destination address to match the rule but want to specify SNAT, simply use a colon followed by the SNAT address. RATE LIMIT Beginning with Shorewall version 1.4.7, you may rate-limit ACCEPT, DNAT[-], REDIRECT[-] or LOG rules with an entry in this column. Entries have the form <rate>/<interval>[:<burst>] where <rate> is the number of connections per <interval> (sec or min) and <burst> is the largest burst permitted. If no burst value is given, a value of 5 is assumed. There may be no whitespace embedded in the specification. ACCEPT<2/sec:4> net dmz tcp 80 The first time this rule is reached, the packet will be accepted; in fact, since the burst is 4, the first four packets will be accepted. After this, it will be 500ms (1 second divided by the rate of 2) before a packet will be accepted from this rule, regardless of how many packets reach it. Also, every 500ms which passes without matching a packet, one of the bursts will be regained; if no packets hit the rule for 2 second, the burst will be fully recharged; back where we started. When rate limiting is specified on a rule with all in the SOURCE or DEST fields below, the limit will apply to each pair of zones individually rather than as a single limit for all pairs of zones covered by the rule. Rate limiting may also be specified in the ACTION column above; in that case, it must not be specified as part of the RATE LIMIT column. If you want to specify any following columns but no rate limit, place - in this column. USER SET Beginning with Shorewall release 1.4.7, output rules from the firewall itself may be restricted to a particular set of users and/or user groups. See the User Set Documentation for details. #ACTION SOURCE DEST PROTO DEST PORT(S) DNAT<4/min:8> net loc:192.168.1.3 tcp ssh #ACTION SOURCE DEST PROTO DEST PORT(S) SOURCE ORIGINAL # PORT(S) DEST REDIRECT loc 3128 tcp www - !206.124.146.177 ACCEPT fw net tcp www #ACTION SOURCE DEST PROTO DEST PORT(S) ACCEPT net dmz:155.186.235.222 tcp www ACCEPT loc dmz:155.186.235.222 tcp www since the server is in the 192.168.2.0/24 subnetwork, we can assume that access to the server from that subnet will not involve the firewall (but see FAQ 2)unless you have more than one external IP address, you can leave the ORIGINAL DEST column blank in the first rule. You cannot leave it blank in the second rule though because then all ftp connections originating in the local subnet 192.168.1.0/24 would be sent to 192.168.2.2 regardless of the site that the user was trying to connect to. That is clearly not what you want. #ACTION SOURCE DEST PROTO DEST PORT(S) SOURCE ORIGINAL # PORT(S) DEST DNAT net dmz:192.168.2.2 tcp ftp DNAT loc:192.168.1.0/24 dmz:192.168.2.2 tcp ftp - 155.186.235.151 If you are running wu-ftpd, you should restrict the range of passive in your /etc/ftpaccess file. I only need a few simultaneous FTP sessions so I use port range 65500-65535. In /etc/ftpaccess, this entry is appropriate: passive ports 0.0.0.0/0 65500 65534 If you are running pure-ftpd, you would include -p 65500:65534 on the pure-ftpd runline. The important point here is to ensure that the port range used for FTP passive connections is unique and will not overlap with any usage on the firewall system. #ACTION SOURCE DEST PROTO DEST PORT(S) ACCEPT loc:~02-00-08-E3-FA-55 dmz all #ACTION SOURCE DEST PROTO DEST PORT(S) ACCEPT all dmz tcp 25 When all is used as a source or destination, intra-zone traffic is not affected. In this example, if there were two DMZ interfaces then the above rule would NOT enable SMTP traffic between hosts on these interfaces. #ACTION SOURCE DEST PROTO DEST PORT(S) ACCEPT net fw:206.124.146.176 tcp 22 #ACTION SOURCE DEST PROTO DEST PORT(S) SOURCE ORIGINAL # PORT(S) DEST DNAT- net dmz:192.0.2.177 tcp 25 - 192.0.2.178 DNAT- net dmz:192.0.2.177 tcp 25 - 192.0.2.179 ACCEPT net dmz:192.0.2.177 tcp 25 Using DNAT- rather than DNAT avoids two extra copies of the third rule from being generated. #ACTION SOURCE DEST PROTO DEST PORT(S) DNAT net loc:192.168.1.101-192.168.1.109 tcp 80 Look here for information on other services.

Shorewall allows definition of rules that apply between all zones. By default, these rules are defined in the file /etc/shorewall/common.def but may be modified to suit individual requirements. Rather than modify /etc/shorewall/common.def, you should copy that file to /etc/shorewall/common and modify that file. The /etc/shorewall/common file is expected to contain iptables commands; rather than running iptables directly, you should run it indirectly using the Shorewall function run_iptables. That way, if iptables encounters an error, the firewall will be safely stopped.

The /etc/shorewall/masq file is used to define classical IP Masquerading and Source Network Address Translation (SNAT). There is one entry in the file for each subnet that you want to masquerade. In order to make use of this feature, you must have NAT enabled. Columns are: INTERFACE The interface that will masquerade the subnet; this is normally your internet interface. This interface name can be optionally qualified by adding : and a subnet or host IP. When this qualification is added, only packets addressed to that host or subnet will be masqueraded. Beginning with Shorewall version 1.4.10, the interface name can be qualified with ":" followed by a comma separated list of hosts and/or subnets. If this list begins with ! (e.g., eth0:!192.0.2.8/29,192.0.2.32/29) then only packets addressed to destinations not listed will be masqueraded; otherwise (e.g., eth0:192.0.2.8/29,192.0.2.32/29), traffic will be masqueraded if it does match one of the listed addresses. Beginning with Shorewall version 1.3.14, if you have set ADD_SNAT_ALIASES=Yes in , you can cause Shorewall to create an alias label of the form interfacename:digit (e.g., eth0:0) by placing that label in this column. See example 5 below. Alias labels created in this way allow the alias to be visible to the ipconfig utility. THAT IS THE ONLY THING THAT THIS LABEL IS GOOD FOR AND IT MAY NOT APPEAR ANYWHERE ELSE IN YOUR SHOREWALL CONFIGURATION. SUBNET The subnet that you want to have masqueraded through the INTERFACE. This may be expressed as a single IP address, a subnet or an interface name. In the latter instance, the interface must be configured and started before Shorewall is started as Shorewall will determine the subnet based on information obtained from the ip utility. When using Shorewall 1.3.13 or earlier, when an interface name is specified, Shorewall will only masquerade traffic from the first subnetwork on the named interface; if the interface interfaces to more that one subnetwork, you will need to add additional entries to this file for each of those other subnetworks. Beginning with Shorewall 1.3.14, shorewall will masquerade/SNAT traffic from any host that is routed through the named interface. The subnet may be optionally followed by ! and a comma-separated list of addresses and/or subnets that are to be excluded from masquerading. ADDRESS The source address to be used for outgoing packets. This column is optional and if left blank, the current primary IP address of the interface in the first column is used. If you have a static IP on that interface, listing it here makes processing of output packets a little less expensive for the firewall. If you specify an address in this column, it must be an IP address configured on the INTERFACE or you must have ADD_SNAT_ALIASES enabled in . Beginning with Shorewall version 1.4.6, you may include a range of IP addresses in this column to indicate that Netfilter should use the addresses in the range in round-robin fashion. Beginning with Shorewall version 1.4.7, you may include a list of ranges and/or addresses in this column; again, Netfilter will use all listed ranges/addresses in rounde-robin fashion. #INTERFACE SUBNET ADDRESS eth0 192.168.9.0/24 #INTERFACE SUBNET ADDRESS ipsec0:10.1.0.0/16 192.168.9.0/24 #INTERFACE SUBNET ADDRESS eth0 192.168.10.0/24 206.124.146.176 #INTERFACE SUBNET ADDRESS eth0 192.168.10.0/24!192.168.10.44,192.168.10.45 206.124.146.176 #INTERFACE SUBNET ADDRESS eth0:0 192.168.12.0/24 206.124.146.177 #INTERFACE SUBNET ADDRESS eth0 192.168.12.0/24 206.124.146.177,206.124.146.179

If you want to use proxy ARP on an entire sub-network, I suggest that you look at the Proxy ARP Subnet Mini HOWTO. If you decide to use the technique described in that HOWTO, you can set the proxy_arp flag for an interface (/proc/sys/net/ipv4/conf/<interface>/proxy_arp) by including the proxyarp option in the interface's record in . When using Proxy ARP sub-netting, you do NOT include any entries in /etc/shorewall/proxyarp. The /etc/shorewall/proxyarp file is used to define Proxy ARP. The file is typically used for enabling Proxy ARP on a small set of systems since you need one entry in this file for each system using proxy ARP. Columns are: ADDRESS address of the system. INTERFACE the interface that connects to the system. If the interface is obvious from the subnetting, you may enter - in this column. EXTERNAL the external interface that you want to honor ARP requests for the ADDRESS specified in the first column. HAVEROUTE If you already have a route through INTERFACE to ADDRESS, this column should contain Yes or yes. If you want Shorewall to add the route, the column should contain No or no. After you have made a change to the /etc/shorewall/proxyarp file, you may need to flush the ARP cache of all routers on the LAN segment connected to the interface specified in the EXTERNAL column of the change/added entry(s). If you are having problems communicating between an individual host (A) on that segment and a system whose entry has changed, you may need to flush the ARP cache on host A as well. ISPs typically have ARP configured with long TTL (hours!) so if your ISPs router has a stale cache entry (as seen using tcpdump -nei <external interface> host <IP addr>), it may take a long while to time out. I personally have had to contact my ISP and ask them to delete a stale entry in order to restore a system to working order after changing my proxy ARP settings. eth0 - 155.186.235.1 (internet connection) eth1 - 192.168.9.0/24 (masqueraded local systems) eth2 - 192.168.10.1 (interface to your DMZ) In your DMZ, you want to install a Web/FTP server with public address 155.186.235.4. On the Web server, you subnet just like the firewall's eth0 and you configure 155.186.235.1 as the default gateway. In your /etc/shorewall/proxyarp file, you will have: #ADDRESS INTERFACE EXTERNAL HAVEROUTE 155.186.235.4 eth2 eth0 NO You may want to configure the servers in your DMZ with a subnet that is smaller than the subnet of your internet interface. See the Proxy ARP Subnet Mini HOWTO for details. In this case you will want to place Yes in the HAVEROUTE column. Do not use Proxy ARP and FreeS/Wan on the same system unless you are prepared to suffer the consequences. If you start or restart Shorewall with an IPSEC tunnel active, the proxied IP addresses are mistakenly assigned to the IPSEC tunnel device (ipsecX) rather than to the interface that you specify in the INTERFACE column of /etc/shorewall/proxyarp. I haven't had the time to debug this problem so I can't say if it is a bug in the Kernel or in FreeS/Wan. You might be able to work around this problem using the following (I haven't tried it): In /etc/shorewall/init, include: qt /etc/init.d/ipsec stop In /etc/shorewall/start, include: qt /etc/init.d/ipsec start

The /etc/shorewall/nat file is used to define one-to-one NAT. There is one entry in the file for each one-to-one NAT relationship that you wish to define. In order to make use of this feature, you must have NAT enabled. If all you want to do is forward ports to servers behind your firewall, you do NOT want to use one-to-one NAT. Port forwarding can be accomplished with simple entries in the rules file. Also, in most cases Proxy ARP provides a superior solution to one-to-one NAT because the internal systems are accessed using the same IP address internally and externally. Columns in an entry are: EXTERNAL External IP address This should NOT be the primary IP address of the interface named in the next column. INTERFACE Interface that you want the EXTERNAL IP address to appear on. Beginning with Shorewall version 1.3.14, if you have set ADD_IP_ALIASES=Yes in , you can specify an alias label of the form interfacename:digit (e.g., eth0:0) and Shorewall will create the alias with that label. Alias labels created in this way allow the alias to be visible to the ipconfig utility. THAT IS THE ONLY THING THAT THIS LABEL IS GOOD FOR AND IT MAY NOT APPEAR ANYWHERE ELSE IN YOUR SHOREWALL CONFIGURATION. INTERNAL Internal IP address. ALL INTERFACES If Yes or yes (or left empty), NAT will be effective from all hosts. If No or no then NAT will be effective only through the interface named in the INTERFACE column. LOCAL If Yes or yes and the ALL INTERFACES column contains Yes or yes, NAT will be effective from the firewall system. For this to work, you must be running kernel 2.4.19 or later and iptables 1.2.6a or later and you must have enabled CONFIG_IP_NF_NAT_LOCAL in your kernel. Look here for additional information and an example.

The /etc/shorewall/tunnels file allows you to define IPSec, GRE, IPIP, OpenVPN, PPTP and 6to4.tunnels with end-points on your firewall. To use ipsec, you must install version 1.9, 1.91 or the current FreeS/WAN development snapshot. For kernels 2.4.4 and above, you will need to use version 1.91 or a development snapshot as patching with version 1.9 results in kernel compilation errors. Instructions for setting up IPSEC tunnels may be found here, instructions for IPIP and GRE tunnels are here, instructions for OpenVPN tunnels are here, instructions for PPTP tunnels are here, instructions for 6to4 tunnels are here, and instructions for integrating Shorewall with other types of tunnels are here.

This file is used to set the following firewall parameters: MODULE_SUFFIX (Added at version 1.4.9) - The value of this variable determines the possible file extensions of kernel modules. The default value is "o gz ko and o.gz". See for more details. ADMINISABSENTMINDED (Added at version 1.4.7) - The value of this variable affects Shorewall's stopped state. When ADMINISABSENTMINDES=No, only traffic to/from those addresses listed in /etc/shorewall/routestopped is accepted when Shorewall is stopped.When ADMINISABSENTMINDED=Yes, in addition to traffic to/from addresses in /etc/shorewall/routestopped, connections that were active when Shorewall stopped continue to work and all new connections from the firewall system itself are allowed. If this variable is not set or is given the empty value then ADMINISABSENTMINDED=No is assumed. SHOREWALL_SHELL (Added at version 1.4.6) - This parameter is used to specify the shell program to be used to interpret the firewall script (/usr/share/shorewall/firewall). If not specified or specified as a null value, /bin/sh is assumed. LOGFORMAT (Added at version 1.4.4) - The value of this variable generate the --log-prefix setting for Shorewall logging rules. It contains a printf formatting template which accepts three arguments (the chain name, logging rule number (optional) and the disposition). To use LOGFORMAT with fireparse, set it as: LOGFORMAT="fp=%s:%d a=%s " If the LOGFORMAT value contains the substring %d then the logging rule number is calculated and formatted in that position; if that substring is not included then the rule number is not included. If not supplied or supplied as empty (LOGFORMAT="") then Shorewall:%s:%s: is assumed. /sbin/shorewall uses the leading part of the LOGFORMAT string (up to but not including the first %) to find log messages in the show log, status and hits commands. This part should not be omitted (the LOGFORMAT should not begin with %) and the leading part should be sufficiently unique for /sbin/shorewall to identify Shorewall messages. CLEAR_TC (Added at version 1.3.13) - If this option is set to No then Shorewall won't clear the current traffic control rules during [re]start. This setting is intended for use by people that prefer to configure traffic shaping when the network interfaces come up rather than when the firewall is started. If that is what you want to do, set TC_ENABLED=Yes and CLEAR_TC=No and do not supply an /etc/shorewall/tcstart file. That way, your traffic shaping rules can still use the fwmark classifier based on packet marking defined in /etc/shorewall/tcrules. If not specified, CLEAR_TC=Yes is assumed. MARK_IN_FORWARD_CHAIN (Added at version 1.3.12) - If your kernel has a FORWARD chain in the mangle table, you may set MARK_IN_FORWARD_CHAIN=Yes to cause the marking specified in the tcrules file to occur in that chain rather than in the PREROUTING chain. This permits you to mark inbound traffic based on its destination address when SNAT or Masquerading are in use. To determine if your kernel has a FORWARD chain in the mangle table, use the /sbin/shorewall show mangle command; if a FORWARD chain is displayed then your kernel will support this option. If this option is not specified or if it is given the empty value (e.g., MARK_IN_FORWARD_CHAIN="") then MARK_IN_FORWARD_CHAIN=No is assumed. RFC1918_LOG_LEVEL (Added at version 1.3.12) - This parameter determines the level at which packets logged under the norfc1918 mechanism are logged. The value must be a valid syslog level and if no level is given, then info is assumed. Prior to Shorewall version 1.3.12, these packets are always logged at the info level. TCP_FLAGS_DISPOSITION (Added in Version 1.3.11) - Determines the disposition of TCP packets that fail the checks enabled by the tcpflags interface option and must have a value of ACCEPT (accept the packet), REJECT (send an RST response) or DROP (ignore the packet). If not set or if set to the empty value (e.g., TCP_FLAGS_DISPOSITION="") then TCP_FLAGS_DISPOSITION=DROP is assumed. TCP_FLAGS_LOG_LEVEL (Added in Version 1.3.11) - Determines the syslog level for logging packets that fail the checks enabled by the tcpflags interface option.The value must be a valid syslogd log level. If you don't want to log these packets, set to the empty value (e.g., TCP_FLAGS_LOG_LEVEL=""). MACLIST_DISPOSITION (Added in Version 1.3.10) - Determines the disposition of connections requests that fail MAC Verification and must have the value ACCEPT (accept the connection request anyway), REJECT (reject the connection request) or DROP (ignore the connection request). If not set or if set to the empty value (e.g., MACLIST_DISPOSITION="") then MACLIST_DISPOSITION=REJECT is assumed. MACLIST_LOG_LEVEL (Added in Version 1.3.10) - Determines the syslog level for logging connection requests that fail MAC Verification. The value must be a valid syslogd log level. If you don't want to log these connection requests, set to the empty value (e.g., MACLIST_LOG_LEVEL=""). NEWNOTSYN (Added in Version 1.3.8) - When set to Yes or yes, Shorewall will filter TCP packets that are not part of an established connention and that are not SYN packets (SYN flag on - ACK flag off). If set to No, Shorewall will silently drop such packets. If not set or set to the empty value (e.g., NEWNOTSYN=), NEWNOTSYN=No is assumed. If you have a HA setup with failover to another firewall, you should have NEWNOTSYN=Yes on both firewalls. You should also select NEWNOTSYN=Yes if you have asymmetric routing. LOGNEWNOTSYN (Added in Version 1.3.6) - Beginning with version 1.3.6, Shorewall drops non-SYN TCP packets that are not part of an existing connection. If you would like to log these packets, set LOGNEWNOTSYN to the syslog level at which you want the packets logged. Example: LOGNEWNOTSYN=ULOG| Packets logged under this option are usually the result of broken remote IP stacks rather than the result of any sort of attempt to breach your firewall. DETECT_DNAT_ADDRS (Added in Version 1.3.4) - If set to Yes or yes, Shorewall will detect the first IP address of the interface to the source zone and will include this address in DNAT rules as the original destination IP address. If set to No or no, Shorewall will not detect this address and any destination IP address will match the DNAT rule. If not specified or empty, DETECT_DNAT_ADDRS=Yes is assumed. MULTIPORT Removed in version 1.4.6 -- the value of this parameter is now automatically detected by Shorewall If set to Yes or yes, Shorewall will use the Netfilter multiport facility. In order to use this facility, your kernel must have multiport support (CONFIG_IP_NF_MATCH_MULTIPORT). When this support is used, Shorewall will generate a single rule from each record in the /etc/shorewall/rules file that meets these criteria: No port range(s) specified Specifies 15 or fewer ports Rules not meeting those criteria will continue to generate an individual rule for each listed port or port range. NAT_BEFORE_RULES If set to No or no, port forwarding rules can override the contents of the file. If set to Yes or yes, port forwarding rules cannot override one-to-one NAT. If not set or set to an empty value, Yes is assumed. FW This parameter specifies the name of the firewall zone. If not set or if set to an empty string, the value fw is assumed. SUBSYSLOCK This parameter should be set to the name of a file that the firewall should create if it starts successfully and remove when it stops. Creating and removing this file allows Shorewall to work with your distribution's initscripts. For RedHat, this should be set to /var/lock/subsys/shorewall. For Debian, the value is /var/state/shorewall and in LEAF it is /var/run/shorwall. Example: SUBSYSLOCK=/var/lock/subsys/shorewall. STATEDIR This parameter specifies the name of a directory where Shorewall stores state information. If the directory doesn't exist when Shorewall starts, it will create the directory. Example: STATEDIR=/tmp/shorewall. If you change the STATEDIR variable while the firewall is running, create the new directory if necessary then copy the contents of the old directory to the new directory. MODULESDIR This parameter specifies the directory where your kernel netfilter modules may be found. If you leave the variable empty, Shorewall will supply the value "/lib/modules/`uname -r`/kernel/net/ipv4/netfilter. LOGRATE and LOGBURST These parameters set the match rate and initial burst size for logged packets. Please see the iptables man page for a description of the behavior of these parameters (the iptables option --limit is set by LOGRATE and --limit-burst is set by LOGBURST). If both parameters are set empty, no rate-limiting will occur. LOGRATE=10/minute LOGBURST=5 LOGFILE This parameter tells the /sbin/shorewall program where to look for Shorewall messages when processing the show log, monitor, status and hits commands. If not assigned or if assigned an empty value, /var/log/messages is assumed. NAT_ENABLED Removed in Shorewall 1.4.6 -- the value of this parameter is now automatically detected by Shorewall This parameter determines whether Shorewall supports NAT operations. NAT operations include: One-to-one NAT Port Forwarding Port Redirection Masquerading If the parameter has no value or has a value of Yes or yes then NAT is enabled. If the parameter has a value of no or No then NAT is disabled. MANGLE_ENABLED Removed in Shorewall 1.4.6 -- the value of this parameter is now automatically detected by Shorewall This parameter determines if packet mangling is enabled. If the parameter has no value or has a value of Yes or yes than packet mangling is enabled. If the parameter has a value of no or No then packet mangling is disabled. If packet mangling is disabled, the /etc/shorewall/tos file is ignored. IP_FORWARDING This parameter determines whether Shorewall enables or disables IPV4 Packet Forwarding (/proc/sys/net/ipv4/ip_forward). Possible values are: On or on packet forwarding will be enabled. Off or off packet forwarding will be disabled. Keep or keep Shorewall will neither enable nor disable packet forwarding. If this variable is not set or is given an empty value (IP_FORWARD="") then IP_FORWARD=On is assumed. ADD_IP_ALIASES This parameter determines whether Shorewall automatically adds the external address(es) in . If the variable is set to Yes or yes then Shorewall automatically adds these aliases. If it is set to No or no, you must add these aliases yourself using your distribution's network configuration tools. Shorewall versions before 1.4.6 can only add addresses to the first subnetwork configured on an interface. If this variable is not set or is given an empty value (ADD_IP_ALIASES="") then ADD_IP_ALIASES=Yes is assumed. ADD_SNAT_ALIASES This parameter determines whether Shorewall automatically adds the SNAT ADDRESS in . If the variable is set to Yes or yes then Shorewall automatically adds these addresses. If it is set to No or no, you must add these addresses yourself using your distribution's network configuration tools. Shorewall versions before 1.4.6 can only add addresses to the first subnetwork configured on an interface. If this variable is not set or is given an empty value (ADD_SNAT_ALIASES="") then ADD_SNAT_ALIASES=No is assumed. LOGUNCLEAN This parameter determines the logging level of mangled/invalid packets controlled by the dropunclean and logunclean interface options. If LOGUNCLEAN is empty (LOGUNCLEAN=) then packets selected by dropclean are dropped silently (logunclean packets are logged under the info log level). Otherwise, these packets are logged at the specified level (Example: LOGUNCLEAN=debug). BLACKLIST_DISPOSITION This parameter determines the disposition of packets from blacklisted hosts. It may have the value DROP if the packets are to be dropped or REJECT if the packets are to be replied with an ICMP port unreachable reply or a TCP RST (tcp only). If you do not assign a value or if you assign an empty value then DROP is assumed. BLACKLIST_LOGLEVEL This paremter determines if packets from blacklisted hosts are logged and it determines the syslog level that they are to be logged at. Its value is a syslog level (Example: BLACKLIST_LOGLEVEL=debug). If you do not assign a value or if you assign an empty value then packets from blacklisted hosts are not logged. CLAMPMSS This parameter enables the TCP Clamp MSS to PMTU feature of Netfilter and is usually required when your internet connection is through PPPoE or PPTP. If set to Yes or yes, the feature is enabled. If left blank or set to No or no, the feature is not enabled. This option requires CONFIG_IP_NF_TARGET_TCPMSS in your kernel. ROUTE_FILTER If this parameter is given the value Yes or yes then route filtering (anti-spoofing) is enabled on all network interfaces. The default value is no.

The file /etc/shorewall/modules contains commands for loading the kernel modules required by Shorewall-defined firewall rules. Shorewall will source this file during start/restart provided that it exists and that the directory specified by the MODULESDIR parameter exists (see above). The file that is released with Shorewall calls the Shorewall function loadmodule for the set of modules that I load. The loadmodule function is called as follows: loadmodule <modulename> [ <module parameters> ] where <modulename> is the name of the modules without the trailing .o (example ip_conntrack). <module parameters> Optional parameters to the insmod utility. The function determines if the module named by <modulename> is already loaded and if not then the function determines if the .o file corresponding to the module exists in the <moduledirectory>; if so, then the following command is executed: insmod <moduledirectory>/<modulename>.o <module parameters> If the file doesn't exist, the function determines of the .o.gz file corresponding to the module exists in the moduledirectory. If it does, the function assumes that the running configuration supports compressed modules and execute the following command: insmod <moduledirectory>/<modulename>.o.gz <module parameters> Beginning with the 1.4.9 Shorewall release, the value of the MODULE_SUFFIX option in determines which files the loadmodule function looks for if the named module doesn't exist. For each file <extension> listed in MODULE_SUFFIX (default "o gz ko o.gz"), the function will append a period (".") and the extension and if the resulting file exists then the following command will be executed: insmod moduledirectory/<modulename>.<extension> <module parameters>

The /etc/shorewall/tos file allows you to set the Type of Service field in packet headers based on packet source, packet destination, protocol, source port and destination port. In order for this file to be processed by Shorewall, you must have mangle support enabled. Entries in the file have the following columns: SOURCE The source zone. May be qualified by following the zone name with a colon (:) and either an IP address, an IP subnet, a MAC address in Shorewall Format or the name of an interface. This column may also contain the name of the firewall zone to indicate packets originating on the firewall itself or all to indicate any source. DEST The destination zone. May be qualified by following the zone name with a colon (:) and either an IP address or an IP subnet. Because packets are marked prior to routing, you may not specify the name of an interface. This column may also contain all to indicate any destination. PROTOCOL The name of a protocol in /etc/protocols or the protocol's number. SOURCE PORT(S) The source port or a port range. For all ports, place a hyphen (-) in this column. DEST PORT(S) The destination port or a port range. To indicate all ports, place a hyphen (-) in this column. TOS The type of service. Must be one of the following: Minimize-Delay (16) Maximize-Throughput (8) Maximize-Reliability (4) Minimize-Cost (2) Normal-Service (0) /etc/shorewall/tos file that is included with Shorewall #SOURCE DEST PROTOCOL SOURCE PORTS(S) DEST PORTS(S) TOS all all tcp - ssh 16 all all tcp ssh - 16 all all tcp - ftp 16 all all tcp ftp - 16 all all tcp - ftp-data 8 all all tcp ftp-data - 8 Users have reported that odd routing problems result from adding the ESP and AH protocols to the /etc/shorewall/tos file.

Each line in /etc/shorewall/blacklist contains an IP address, a MAC address in Shorewall Format or subnet address. 130.252.100.69 206.124.146.0/24 Packets from hosts listed in the blacklist file will be disposed of according to the value assigned to the BLACKLIST_DISPOSITION and BLACKLIST_LOGLEVEL variables in /etc/shorewall/shorewall.conf. Only packets arriving on interfaces that have the blacklist option in /etc/shorewall/interfaces are checked against the blacklist. The black list is designed to prevent listed hosts/subnets from accessing services on your network. Beginning with Shorewall 1.3.8, the blacklist file has three columns: ADDRESS/SUBNET As described above. PROTOCOL Optional. If specified, only packets specifying this protocol will be blocked. PORTS Optional; may only be given if PROTOCOL is tcp, udp or icmp. Expressed as a comma-separated list of port numbers or service names (from /etc/services). If present, only packets destined for the specified protocol and one of the listed ports are blocked. When the PROTOCOL is icmp, the PORTS column contains a comma-separated list of ICMP type numbers or names (see iptables -h icmp). Shorewall also has a dynamic blacklist capability. The Shorewall blacklist file is NOT designed to police your users' web browsing -- to do that, I suggest that you install and configure Squid with SquidGuard.

This file lists the subnets affected by the norfc1918 interface option. Columns in the file are: SUBNET The subnet using VLSM notation (e.g., 192.168.0.0/16). TARGET What to do with packets to/from the SUBNET: RETURN Process the packet normally thru the rules and policies. DROP Silently drop the packet. logdrop Log then drop the packet -- see the RFC1918_LOG_LEVEL parameter above.

This file defines the hosts that are accessible from the firewall when the firewall is stopped. Columns in the file are: INTERFACE The firewall interface through which the host(s) comminicate with the firewall. HOST(S) - (Optional) A comma-separated list of IP/Subnet addresses. If not supplied or supplied as - then 0.0.0.0/0 is assumed. #INTERFACE HOST(S) eth2 192.168.1.0/24 eth1 -

This file is described in the MAC Validation Documentation.

This file is described in the ECN Control Documentation.

These files are described in theUID/GID-based Rules Documentation .

This file is described in the Traffic Accounting Documentation.

1.122004-01-21TEAdd masquerade destination list.1.122004-01-18TECorrect typo.1.112004-01-05TEStandards Compliance1.102004-01-05TEImproved formatting of DNAT- and REDIRECT- for clarity1.92003-12-25MNInitial Docbook Conversion Complete