Copyright © 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”.
2004-02-03
Abstract
This documentation is intended primarily for reference. Step-by-step instructions for configuring Shorewall in common setups may be found in the QuickStart Guides.
Table of Contents
Shorewall consists of the following components:
a parameter file installed in /etc/shorewall that can be used to establish the values of shell variables for use in other files.
a parameter file installed in /etc/shorewall that is used to set several firewall parameters.
a parameter file installed in /etc/shorewall that defines a network partitioning into “zones”
a parameter file installed in /etc/shorewall that establishes overall firewall policy.
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.
a parameter file installed in /etc/shorewall and used to list blacklisted IP/subnet/MAC addresses.
a parameter file installed in /etc/shorewall and used to selectively disable Explicit Congestion Notification (ECN - RFC 3168).
a set of shell functions used by both the firewall and shorewall shell programs. Installed in /usr/share/shorewall.
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.
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.
a shell script installed in /etc/init.d to automatically start Shorewall during boot. The particular script installed depends on which distribution you are running.
a parameter file installed in /etc/shorewall and used to describe the interfaces on the firewall system.
a parameter file installed in /etc/shorewall and used to describe individual hosts or subnetworks in zones.
a parameter file installed in /etc/shorewall and used to verify the MAC address (and possibly also the IP address(es)) of devices.
This file also describes IP masquerading under Shorewall and is installed in /etc/shorewall.
a shell program that reads the configuration files in /etc/shorewall and configures your firewall. This file is installed in /usr/share/shorewall.
a parameter file in /etc/shorewall used to define one-to-one NAT.
a parameter file in /etc/shorewall used to define Proxy Arp.
a parameter file in /etc/shorewall used to define the treatment of packets under the norfc1918 interface option.
a parameter file in /etc/shorewall used to define those hosts that can access the firewall when Shorewall is stopped.
a parameter file in /etc/shorewall used to define rules for classifying packets for Traffic Shaping/Control.
a parameter file in /etc/shorewall used to define IPSec tunnels.
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).
a parameter file in /etc/shorewall used to define traffic accounting rules. This file was added in version 1.4.7.
a file created in /usr/share/shorewall that describes the version of Shorewall installed on your system.
files in /etc/shorewall that allow you to define your own actions for rules in /etc/shorewall/rules.
files in /etc/shorewall that define the actions included as a standard part of Shorewall.
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
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:
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 /etc/shorewall/shorewall.conf.
The name of the zone as displayed during Shorewall startup.
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:
A zone defined in the /etc/shorewall/zones file or “-”. If you specify “-”, you must use the /etc/shorewall/hosts file to define the zones accessed via this interface.
the name of the interface (examples: eth0, ppp0, ipsec+). Each interface can be listed on only one record in this file.
You do not need to include the loopback interface (lo) in this file.
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).
a comma-separated list of options. Possible options include:
(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.
(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 /etc/shorewall/shorewall.conf.
(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 “-”.
(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 /etc/shorewall/shorewall.conf and are disposed of according to the TCP_FLAGS_DISPOSITION option.
This option causes incoming packets on this interface to be checked against the blacklist.
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).
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.
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.
(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 /etc/shorewall/proxyarp.
(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.
(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.
(Added in version 2.0.0) - If this option is specified, incoming connection requests will be checked to ensure that they do not have a broadcast or multicast address as their source. Any such packets will be dropped after being optionally logged according to the setting of SMURF_LOG_LEVEL in /etc/shorewall/shorewall.conf.
My recommendations concerning options:
External Interface -- tcpflags,blacklist,norfc1918,routefilter,nosmurfs
Wireless Interface -- maclist,routefilter,tcpflags,detectnets,nosmurfs
Use dhcp and proxyarp when needed.
Example 3. You have a conventional firewall setup in which eth0 connects to a Cable or DSL modem and eth1 connects to your local network and eth0 gets its IP address via DHCP. You want to check all packets entering from the internet against the black list. Your /etc/shorewall/interfaces file would be as follows:
#ZONE INTERFACE BROADCAST OPTIONS net eth0 detect dhcp,norfc1918,blacklist |
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:
A zone defined in the /etc/shorewall/zones file.
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.
A comma-separated list of option
(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.
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.
Example 6. Your local interface is eth1 and you have two groups of local hosts that you want to make into separate zones:
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 |
Example 7. You have local interface eth1 with two IP addresses - 192.168.1.1/24 and 192.168.12.1/24
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:
The connection is allowed.
The connection request is ignored.
The connection request is rejected with an RST (TCP) or an ICMP destination-unreachable packet being returned to the client.
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.
(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:
The name of a client zone (a zone defined in the /etc/shorewall/zones file , the name of the firewall zone or “all”).
The name of a destination zone (a zone defined in the /etc/shorewall/zones 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.
The default policy for connection requests from the SOURCE zone to the DESTINATION zone.
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.
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.
Beginning with Shorewall 2.0.0, you can control the traffic from the firewall to itself. As with any zone, fw->fw traffic is enabled by default. It is not necessary to define the loopback interface (lo) in /etc/shorewall/interfaces in order to define fw->fw rules or a fw->fw policy.
So long as there are no intra-zone rules for a zone, all intra-zone traffic for that zone is accepted. As soon as you add a single rule from the zone to itself, then ALL traffic from that zone to itself is controlled by the rules and the first policy in /etc/shorewall/policy that matches the zone to itself.
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. Entries in this file only govern the establishment of new connections — packets that are part of an existing connection or that establish a connection that is related to an existing connection are automatically accepted.
Rules for each pair of zones (source zone, destination zone) are evaluated in the order that they appear in the file — the first match determines the disposition of the connection request with a couple of caveats:
LOG rules cause the connection request to be logged then processing continues with the next rule in the file.
QUEUE rules cause the connection request to be passed to user-space -- the user-space application can later insert them back into the stream for further processing by following rules.
CONTINUE rules may cause the connection request to be reprocessed using a different (source zone, destination zone) pair.
Entries in the file have the following columns:
These have the same meaning here as in the policy file above.
Causes the connection request to be forwarded to the system specified in the DEST column (port forwarding). “DNAT” stands for “Destination Network Address Translation”
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.
Causes the connection request to be redirected to a port on the local (firewall) system.
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 the packet -- requires a syslog level (see below).
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.
(Shorewall 1.4.9 and later) - An action defined in the /etc/shorewall/actions file.
The ACTION may optionally be followed by “:” and a syslog level (example: REJECT:info or ACCEPT:debug). 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 in your kernel configuration.
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:
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).
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.
in Shorewall format.
refers to a connection request from any host in the specified subnet (example net:155.186.235.0/24).
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-.
Protocol. Must be a protocol name from /etc/protocols, a number or “all”. Specifies the protocol of the connection request.
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.
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.
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.
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.
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.
Example 9. Let's take
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.
If you want to specify any following columns but no rate limit, place “-” in this column.
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.
Example 10. You wish to forward all ssh connection requests from the internet to local system 192.168.1.3. You wish to limit the number of connections to 4/minute with a burst of 8 (Shorewall 1.4.7 and later only):
#ACTION SOURCE DEST PROTO DEST PORT(S) DNAT<4/min:8> net loc:192.168.1.3 tcp ssh |
Example 11. You want to redirect all local www connection requests EXCEPT those to your own http server (206.124.146.177) to a Squid transparent proxy running on the firewall and listening on port 3128. Squid will of course require access to remote web servers. This example shows yet another use for the ORIGINAL DEST column; here, connection requests that were NOT (notice the “!”) originally destined to 206.124.146.177 are redirected to local port 3128.
#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 |
Example 12. You want to run a web server at 155.186.235.222 in your DMZ and have it accessible remotely and locally. the DMZ is managed by Proxy ARP or by classical sub-netting.
#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 |
Example 13. You want to run wu-ftpd on 192.168.2.2 in your masqueraded DMZ. Your internet interface address is 155.186.235.151 and you want the FTP server to be accessible from the internet in addition to the local 192.168.1.0/24 and dmz 192.168.2.0/24 subnetworks.
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.
Example 14. You wish to allow unlimited DMZ access to the host with MAC address 02:00:08:E3:FA:55.
#ACTION SOURCE DEST PROTO DEST PORT(S) ACCEPT loc:~02-00-08-E3-FA-55 dmz all |
Example 15. You wish to allow access to the SMTP server in your DMZ from all zones.
#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.
Example 16. Your firewall's external interface has several IP addresses but you only want to accept SSH connections on address 206.124.146.176.
#ACTION SOURCE DEST PROTO DEST PORT(S) ACCEPT net fw:206.124.146.176 tcp 22 |
Example 17. (For advanced users running Shorewall version 1.3.13 or later). From the internet, you with to forward tcp port 25 directed to 192.0.2.178 and 192.0.2.179 to host 192.0.2.177 in your DMZ. You also want to allow access from the internet directly to tcp port 25 on 192.0.2.177.
#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.
Example 18. (Shorewall version 1.4.6 or later). You have 9 http servers behind a Shorewall firewall and you want connection requests to be distributed among your servers. The servers are 192.168.1.101-192.168.1.109.
#ACTION SOURCE DEST PROTO DEST PORT(S) DNAT net loc:192.168.1.101-192.168.1.109 tcp 80 |
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:
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 /etc/shorewall/shorewall.conf, 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.
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.
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 /etc/shorewall/shorewall.conf. 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.
Example 19. You have eth0 connected to a cable modem and eth1 connected to your local subnetwork 192.168.9.0/24. Your /etc/shorewall/masq file would look like:
#INTERFACE SUBNET ADDRESS eth0 192.168.9.0/24 |
Example 20. You have a number of IPSEC tunnels through ipsec0 and you want to masquerade traffic from your 192.168.9.0/24 subnet to the remote subnet 10.1.0.0/16 only.
#INTERFACE SUBNET ADDRESS ipsec0:10.1.0.0/16 192.168.9.0/24 |
Example 21. You have a DSL line connected on eth0 and a local network (192.168.10.0/24) connected to eth1. You want all local->net connections to use source address 206.124.146.176.
#INTERFACE SUBNET ADDRESS eth0 192.168.10.0/24 206.124.146.176 |
Example 22. Same as example 3 except that you wish to exclude 192.168.10.44 and 192.168.10.45 from the SNAT rule.
#INTERFACE SUBNET ADDRESS eth0 192.168.10.0/24!192.168.10.44,192.168.10.45 206.124.146.176 |
Example 23. (Shorewall version >= 1.3.14): You have a second IP address (206.124.146.177) assigned to you and wish to use it for SNAT of the subnet 192.168.12.0/24. You want to give that address the name eth0:0. You must have ADD_SNAT_ALIASES=Yes in /etc/shorewall/shorewall.conf.
#INTERFACE SUBNET ADDRESS eth0:0 192.168.12.0/24 206.124.146.177 |
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 /etc/shorewall/interfaces. 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 of the system.
the interface that connects to the system. If the interface is obvious from the subnetting, you may enter “-” in this column.
the external interface that you want to honor ARP requests for the ADDRESS specified in the first column.
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”.
If you specify "No" or "no" in the HAVEROUTE column, Shorewall will automatically add a route to the host in the ADDRESS column through the interface in the INTERFACE column. If you enter “No” or “no” in the PERSISTENT column or if you leave the column empty, that route will be deleted if you issue a shorewall stop or shorewall clear command. If you place “Yes” or “yes” in the PERSISTENT column, then those commands will not cause the route to be deleted.
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.
Example 25. You have public IP addresses 155.182.235.0/28. You configure your firewall as follows:
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 IP address
This should NOT be the primary IP address of the interface named in the next column.
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 /etc/shorewall/shorewall.conf, 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 IP address.
If “Yes” or “yes”, NAT will be effective from all hosts. If “No” or “no” (or if left empty) then NAT will be effective only through the interface named in the INTERFACE column.
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.
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:
(Added at version 2.0.0) - Specifies the logging level for smurf packets (see the nosmurfs option in /etc/shorewall/interfaces). If set to the empty value ( SMURF_LOG_LEVEL="" ) then smurfs are not logged.
(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 /etc/shorewall/modules for more details.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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="").
(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.
(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="").
(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.
(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.
(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.
If set to “No” or “no”, port forwarding rules can override the contents of the /etc/shorewall/nat 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.
This parameter specifies the name of the firewall zone. If not set or if set to an empty string, the value “fw” is assumed.
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.
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.
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.
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.
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.
This parameter determines whether Shorewall enables or disables IPV4 Packet Forwarding (/proc/sys/net/ipv4/ip_forward). Possible values are:
packet forwarding will be enabled.
packet forwarding will be disabled.
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.
This parameter determines whether Shorewall automatically adds the external address(es) in /etc/shorewall/nat. 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.
If this variable is not set or is given an empty value (ADD_IP_ALIASES="") then ADD_IP_ALIASES=Yes is assumed.
This parameter determines whether Shorewall automatically adds the SNAT ADDRESS in /etc/shorewall/masq. 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.
If this variable is not set or is given an empty value (ADD_SNAT_ALIASES="") then ADD_SNAT_ALIASES=No is assumed.
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).
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.
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.
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.
If this parameter is given the value “Yes” or “yes” then route filtering (anti-spoofing) is enabled on all network interfaces which are brought up while Shorewall is in the started state. 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 /etc/shorewall/shorewall.conf 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
is the name of the modules without the trailing “.o” (example ip_conntrack).
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:
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.
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.
The name of a protocol in /etc/protocols or the protocol's number.
The source port or a port range. For all ports, place a hyphen (“-”) in this column.
The destination port or a port range. To indicate all ports, place a hyphen (“-”) in this column.
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.
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:
As described above.
Optional. If specified, only packets specifying this protocol will be blocked.
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:
The subnet using VLSM notation (e.g., 192.168.0.0/16).
What to do with packets to/from the SUBNET:
Process the packet normally thru the rules and policies.
Silently drop the packet.
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:
The firewall interface through which the host(s) comminicate with the firewall.
A comma-separated list of IP/Subnet addresses. If not supplied or supplied as “-” then 0.0.0.0/0 is assumed.
This file is described in the MAC Validation Documentation.
This file is described in the ECN Control Documentation.
This file is described in the Traffic Accounting Documentation.
| Revision History | ||
|---|---|---|
| Revision 1.14 | 2004-02-13 | TE |
| Add a note about the order of rules. | ||
| Revision 1.13 | 2004-02-03 | TE |
| Update for Shorewall 2.0. | ||
| Revision 1.12 | 2004-01-21 | TE |
| Add masquerade destination list. | ||
| Revision 1.12 | 2004-01-18 | TE |
| Correct typo. | ||
| Revision 1.11 | 2004-01-05 | TE |
| Standards Compliance | ||
| Revision 1.10 | 2004-01-05 | TE |
| Improved formatting of DNAT- and REDIRECT- for clarity | ||
| Revision 1.9 | 2003-12-25 | MN |
| Initial Docbook Conversion Complete | ||