Configuration Files
Tom
Eastep
2001-2006
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 article applies to Shorewall 3.0 and
later. If you are running a version of Shorewall earlier than Shorewall
3.0.0 then please see the documentation for that
release.
If you copy or edit your configuration files on a system running
Microsoft Windows, you must run them through dos2unix
before you use them with Shorewall.
Files
/etc/shorewall/shorewall.conf - used to
set several firewall parameters.
/etc/shorewall/params - use this file to
set shell variables that you will expand in other files.
/etc/shorewall/zones - partition the
firewall's view of the world into zones.
/etc/shorewall/policy - establishes
firewall high-level policy.
/etc/shorewall/interfaces - describes the
interfaces on the firewall system.
/etc/shorewall/hosts - allows defining
zones in terms of individual hosts and subnetworks.
/etc/shorewall/masq - directs the
firewall where to use many-to-one (dynamic) Network Address
Translation (a.k.a. Masquerading) and Source Network Address
Translation (SNAT).
/etc/shorewall/modules - directs the
firewall to load kernel modules.
/etc/shorewall/rules - defines rules that
are exceptions to the overall policies established in
/etc/shorewall/policy.
/etc/shorewall/nat - defines one-to-one
NAT rules.
/etc/shorewall/proxyarp - defines use of
Proxy ARP.
/etc/shorewall/routestopped - defines
hosts accessible when Shorewall is stopped.
/etc/shorewall/tcrules - defines marking
of packets for later use by traffic control/shaping or policy
routing.
/etc/shorewall/tos - defines rules for
setting the TOS field in packet headers.
/etc/shorewall/tunnels - defines tunnels
(VPN) with end-points on the firewall system.
/etc/shorewall/blacklist - lists
blacklisted IP/subnet/MAC addresses.
/etc/shorewall/init - commands that you
wish to execute at the beginning of a shorewall start
or shorewall restart
.
/etc/shorewall/start - commands that you
wish to execute at the completion of a shorewall
start
or shorewall restart
/etc/shorewall/stop - commands that you
wish to execute at the beginning of a shorewall
stop
.
/etc/shorewall/stopped - commands that
you wish to execute at the completion of a shorewall
stop
.
/etc/shorewall/ecn - disable Explicit
Congestion Notification (ECN - RFC 3168) to remote hosts or
networks.
/etc/shorewall/accounting - define IP
traffic accounting rules
/etc/shorewall/actions and
/usr/share/shorewall/action.template allow
user-defined actions.
/etc/shorewall/providers - defines an
alternate routing table.
/etc/shorewall/route_rules (Added in
Shorewall 3.2.0) - Defines routing rules to be used in conjunction
with the routing tables devined in
/etc/shorewall/providers.
/usr/share/shorewall/actions.std -
Actions defined by Shorewall.
/usr/share/shorewall/action.* - Details
of actions defined by Shorewall.
/usr/share/shorewall/macro.* - Details of
macros defined by Shorewall.
/usr/share/rfc1918 — Defines the behavior
of the 'norfc1918' interface option in
/etc/shorewall/interfaces. If you need to change this file, copy it to
/etc/shorewall and modify the
copy.
Man Pages
Beginning with Shorewall version 3.4, man pages are provided in
section 5 for each of the Shorewall configuration files. The name of the
page is formed by prefixing the file name with "shorewall-".
Example — To view the manual page for
/etc/shorewall/interfaces:
man shorewall-interfaces
The /etc/shorewall/shorewall.conf file is an exception -- the man
page for that file is 'shorewall.conf':
man shorewall.conf
Line Continuation
You may continue lines in the configuration files using the usual
backslash (\
) followed immediately by a new line character
(Enter key).
Line Continuation
ACCEPT net $FW tcp \↵
smtp,www,pop3,imap #Services running on the firewall
INCLUDE Directive
Any configuration file may contain INCLUDE directives (INCLUDE is
not supported in extension
scripts). An INCLUDE directive consists of the word INCLUDE
followed by a path name and causes the contents of the named file to be
logically included into the file containing the INCLUDE. Relative path
names given in an INCLUDE directive are assumed to reside in
/etc/shorewall or in an alternate configuration directory if one has been
specified for the command.
INCLUDE's may be nested to a level of 3 -- further nested INCLUDE
directives are ignored with a warning message.
Use of INCLUDE
shorewall/params.mgmt:
MGMT_SERVERS=1.1.1.1,2.2.2.2,3.3.3.3
TIME_SERVERS=4.4.4.4
BACKUP_SERVERS=5.5.5.5
----- end params.mgmt -----
shorewall/params:
# Shorewall 1.3 /etc/shorewall/params
[..]
#######################################
INCLUDE params.mgmt
# params unique to this host here
#LAST LINE - ADD YOUR ENTRIES ABOVE THIS ONE - DO NOT REMOVE
----- end params -----
shorewall/rules.mgmt:
ACCEPT net:$MGMT_SERVERS $FW tcp 22
ACCEPT $FW net:$TIME_SERVERS udp 123
ACCEPT $FW net:$BACKUP_SERVERS tcp 22
----- end rules.mgmt -----
shorewall/rules:
# Shorewall version 1.3 - Rules File
[..]
#######################################
INCLUDE rules.mgmt
# rules unique to this host here
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE
----- end rules -----
Using DNS Names
I personally recommend strongly against using DNS names in
Shorewall configuration files. If you use DNS names and you are called
out of bed at 2:00AM because Shorewall won't start as a result of DNS
problems then don't say that you were not forewarned.
Host addresses in Shorewall configuration files may be specified as
either IP addresses or DNS Names.
DNS names in iptables rules aren't nearly as useful as they first
appear. When a DNS name appears in a rule, the iptables utility resolves
the name to one or more IP addresses and inserts those addresses into the
rule. So changes in the DNS->IP address relationship that occur after
the firewall has started have absolutely no effect on the firewall's
ruleset.
If your firewall rules include DNS names then:
If your /etc/resolv.conf is wrong then your
firewall won't start.
If your /etc/nsswitch.conf is wrong then
your firewall won't start.
If your Name Server(s) is(are) down then your firewall won't
start.
If your startup scripts try to start your firewall before
starting your DNS server then your firewall won't start.
Factors totally outside your control (your ISP's router is down
for example), can prevent your firewall from starting.
You must bring up your network interfaces prior to starting your
firewall.
Each DNS name must be fully qualified and include a minimum of two
periods (although one may be trailing). This restriction is imposed by
Shorewall to insure backward compatibility with existing configuration
files.
Valid DNS Names
mail.shorewall.net
shorewall.net. (note the trailing period).
Invalid DNS Names
mail (not fully qualified)
shorewall.net (only one period)
DNS names may not be used as:
The server address in a DNAT rule (/etc/shorewall/rules
file)
In the ADDRESS column of an entry in /etc/shorewall/masq.
In the /etc/shorewall/nat file.
These restrictions are imposed by Netfilter and not by
Shorewall.
Comma-separated Lists
Comma-separated lists are allowed in a number of contexts within the
configuration files. A comma separated list:
Must not have any embedded white space. Valid: routefilter,dhcp,norfc1918
Invalid: routefilter, dhcp, norfc1818
If you use line continuation to break a comma-separated list,
the continuation line(s) must begin in column 1 (or there would be
embedded white space)
Entries in a comma-separated list may appear in any
order.
Complementing an Address or Subnet
Where specifying an IP address, a subnet or an interface, you can
precede the item with !
to specify the complement of the
item. For example, !192.168.1.4 means any host but
192.168.1.4
. There must be no white space following the
!
.
Exclusion Lists
Shorewall 3.0 differs from earlier versions in that in most contexts
where a comma-separated list of addresses is accepted, an
exclusion list may also be included. An exclusion
list is a comma-separated list of addresses that begins with "!".
Example:
!192.168.1.3,192.168.1.12,192.168.1.32/27
The above list refers to "All addresses except 192.168.1.3,
192.168.1.12 and 192.168.1.32-192.168.1.63.
Exclusion lists can also be added after a network address.
Example:
192.168.1.0/24!192.168.1.3,192.168.1.12,192.168.1.32/27
The above list refers to "All addresses in 192.168.1.0-192.168.1.255
except 192.168.1.3, 192.168.1.12 and 192.168.1.32-192.168.1.63.
IP Address Ranges
If you kernel and iptables have iprange match support, you may use
IP address ranges in Shorewall configuration file entries; IP address
ranges have the syntax <low IP
address>-<high IP address>.
Example: 192.168.1.5-192.168.1.12.
To see if your kernel and iptables have the required support, use
the shorewall show capabilities command:
>~ shorewall show capabilities
...
Shorewall has detected the following iptables/netfilter capabilities:
NAT: Available
Packet Mangling: Available
Multi-port Match: Available
Connection Tracking Match: Available
Packet Type Match: Not available
Policy Match: Available
Physdev Match: Available
IP range Match: Available <--------------
Port Numbers/Service Names
Unless otherwise specified, when giving a port number you can use
either an integer or a service name from /etc/services.
Port Ranges
If you need to specify a range of ports, the proper syntax is
<low port number>:<high port number>. For example, if you want
to forward the range of tcp ports 4000 through 4100 to local host
192.168.1.3, the entry in /etc/shorewall/rules is:
#ACTION SOURCE DESTINATION PROTO DEST PORTS(S)
DNAT net loc:192.168.1.3 tcp 4000:4100
If you omit the low port number, a value of zero is assumed; if you
omit the high port number, a value of 65535 is assumed.
Port Lists
In most cases where a port or port range may appear, a
comma-separated list of ports or port ranges may also be entered.
Shorewall will use the Netfilter multiport match capability if it is available (see
the output of "shorewall show
capabilities") and if its use is appropriate.
Shorewall can use multiport match if:
The list contains 15 or fewer port number; and
There are no port ranges listed OR your iptables/kernel support
the Extended multiport match (again
see the output of "shorewall show capabilities").
Where the Extended multiport match is
available, each port range counts as two ports toward the maximum of
15.
Using Shell Variables
You may use the /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
Example:
/etc/shorewall/params
NET_IF=eth0
NET_BCAST=130.252.100.255
NET_OPTIONS=routefilter,norfc1918
/etc/shorewall/interfaces record:
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 routefilter,norfc1918
Variables may be used anywhere in the other configuration
files.
Because the /etc/shorewall/params file is
simply sourced into the shell, you can place arbitrary shell code in the
file and it will be executed each time that the file is read. Any code
included should follow these guidelines:
The code should not have side effects, especially on other
shorewall configuration files.
The code should be safe to execute multiple times without
producing different results.
Should not depend on where the code is called from (the params
file is sourced by both /sbin/shorewall and
/usr/lib/shorewall/firewall).
Should not assume anything about the state of Shorewall.
The names of any functions or variables declared should begin
with an upper case letter.
In Shorewall 3.2, the /etc/shorewall/params
file is processed by the compiler at compile-time and by the compiled
script at run-time. Beginning with Shorewall version 3.2.9, the
/etc/shorewall/params file is pre-processed in
such a way that extra white-space is compressed from the file as it is
being copied into the generated compiler output. So the code in
/etc/shorewall/params should not depend on precise white-space,
including whitespace within quoted strings.
Beginning with Shorewall 3.4.0 RC2,
/etc/shorewall/params is no longer processed by
the compiled script (and extra white-space is no longer compresed from
the file). If you need to set shell variables for use by your run-time
extension script, then set those variables in your
/etc/shorewall/init file.
Using MAC Addresses
Media Access Control (MAC) addresses can be used to specify packet
source in several of the configuration files. In order to control traffic
to/from a host by its MAC address, the host must be on the same network as
the firewall.
To use this feature, your kernel must have MAC Address Match support
(CONFIG_IP_NF_MATCH_MAC) included.
MAC addresses are 48 bits wide and each Ethernet Controller has a
unique MAC address.
In GNU/Linux, MAC addresses are usually written as a series of 6 hex
numbers separated by colons.
MAC Address of an Ethernet Controller
[root@gateway root]# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 02:00:08:E3:FA:55
inet addr:206.124.146.176 Bcast:206.124.146.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:2398102 errors:0 dropped:0 overruns:0 frame:0
TX packets:3044698 errors:0 dropped:0 overruns:0 carrier:0
collisions:30394 txqueuelen:100
RX bytes:419871805 (400.4 Mb) TX bytes:1659782221 (1582.8 Mb)
Interrupt:11 Base address:0x1800
Because Shorewall uses colons as a separator for address fields,
Shorewall requires MAC addresses to be written in another way. In
Shorewall, MAC addresses begin with a tilde (~
) and consist
of 6 hex numbers separated by hyphens. In Shorewall, the MAC address in
the example above would be written ~02-00-08-E3-FA-55.
It is not necessary to use the special Shorewall notation in the
/etc/shorewall/maclist
file.
Shorewall Configurations
Shorewall allows you to have configuration directories other than
/etc/shorewall. The shorewall
check, start and restart commands allow you to specify an alternate
configuration directory and Shorewall will use the files in the alternate
directory rather than the corresponding files in /etc/shorewall. The
alternate directory need not contain a complete configuration; those files
not in the alternate directory will be read from /etc/shorewall.
This facility permits you to easily create a test or temporary
configuration by
copying the files that need modification from /etc/shorewall to
a separate directory;
modify those files in the separate directory; and
specifying the separate directory in a shorewall
start or shorewall restart command (e.g.,
shorewall restart /etc/testconfig )
Saved Configurations
Shorewall allows you to save the
currently-running configuration in a form that permits it to be
re-installed quickly. When you save the configuration using the
shorewall save command, the running configuration is
saved in a file in the /var/lib/shorewall directory. The default
name of that file is /var/lib/shorewall/restore but
you can specify a different name as part of the command. For example, the
command shorewall save standard will save the running
configuration in /var/lib/shorewall/standard. A saved
configuration is re-installed using the shorewall
restore command. Again, that command normally will restore the
configuration saved in /var/lib/shorewall/restore but
as with the save command, you can specify a different
file name in the command. For example, shorewall restore
standard will re-install the configuration saved in
/var/lib/shorewall/standard. By permitting you to
save different configurations under different names, Shorewall provides a
means for quickly switching between these different saved
configurations.
As mentioned above, the default configuration is called 'restore'
but like most things in Shorewall, that default can be changed. The
default name is specified using the RESTOREFILE option in
/etc/shorewall/shorewall.conf.
The default saved configuration is used by Shorewall in a number
of ways besides in the restore command; to avoid
surprises, I recommend that you read the Shorewall Operations
documentation section about saved configurations before creating
one.