MacrosTomEastepCristianRodrÃguez2005Thomas M. EastepPermission 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 4.3 and
later. If you are running a version of Shorewall earlier than Shorewall
4.3.5 then please see the documentation for that
release.Overview of Shorewall Macros?Shorewall macros allow a symbolic name to be associated with a
series of one or more iptables rules. The symbolic name may appear in the
ACTION column of an /etc/shorewall/rules
file entry and in the TARGET column of an action in which case, the
traffic matching that rules file entry will be passed to the series of
iptables rules named by the macro.Macros can be thought of as templates. When a macro is invoked in an
/etc/shorewall/rules entry, it may be qualified by a
logging specification (log level and optionally a log tag). The presence
of the log level/tag causes a modified series of rules to be generated in
which each packet/rule match within the macro causes a log message to be
generated.There are two types of Shorewall macros:Standard Macros. These macros are released as part of Shorewall.
They are defined in macro.* files in /usr/share/shorewall. Each
macro.* file has a comment at the beginning of
the file that describes what the macro does. As an example, here is
the definition of the SMB standard
macro.#
# Shorewall 3.0 /usr/share/shorewall/macro.SMB
#
# Handle Microsoft SMB traffic. You need to invoke this macro in
# both directions.
#
######################################################################################
#TARGET SOURCE DEST PROTO DEST SOURCE RATE USER/
# PORT PORT(S) LIMIT GROUP
PARAM - - udp 135,445
PARAM - - udp 137:139
PARAM - - udp 1024: 137
PARAM - - tcp 135,139,445
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVEIf you wish to modify one of the standard macros, do not modify
the definition in /usr/share/shorewall. Rather, copy the
file to /etc/shorewall (or
somewhere else on your CONFIG_PATH) and modify the copy.User-defined Macros. These macros are created by end-users. They
are defined in macro.* files in /etc/shorewall or in another directory
listed in your CONFIG_PATH (defined in /etc/shorewall/shorewall.conf).Most Standard Macros are parameterized. That
means that you specify what you want to do (ACCEPT, DROP, REJECT, etc.)
when you invoke the macro. The SMB macro shown above is parameterized
(note PARAM in the TARGET column).When invoking a parameterized macro, you follow the name of the
macro with the action that you want to substitute for PARAM enclosed in
parentheses.Example:
/etc/shorewall/rules:#ACTION SOURCE DEST PROTO DEST PORT(S)
SMB(ACCEPT) loc fw The above is equivalent to coding the following series of
rules:#TARGET SOURCE DEST PROTO DEST PORT(s)
ACCEPT loc fw udp 135,445
ACCEPT loc fw udp 137:139
ACCEPT loc fw udp 1024: 137
ACCEPT loc fw tcp 135,139,445
Logging is covered in a following
section. The other columns are treated as follows:SOURCE and DESTIf a value other than "-" appears in both the macro body and
in the invocation of the macro, then the value in the invocation is
examined and the appropriate action is taken. If the value in the
invocation appears to be an address (IP or MAC) or the name of an
ipset, then it is placed after the value in the macro body.
Otherwise, it is placed before the value in the macro body.Example 1:
/etc/shorewall/macro.SMTP#TARGET SOURCE DEST PROTO DEST PORT(S)
PARAM - loc tcp 25/etc/shorewall/rules (Shorewall 4.0):#ACTION SOURCE DEST PROTO DEST PORT(S)
SMTP(DNAT):info net 192.168.1.5/etc/shorewall/rules (Shorewall 4.2.0 and later):#ACTION SOURCE DEST PROTO DEST PORT(S)
SMTP(DNAT):info net 192.168.1.5This would be equivalent to coding the following directly in
/etc/shorewall/rules#ACTION SOURCE DEST PROTO DEST PORT(S)
DNAT:info net loc:192.168.1.5 tcp 25
Example 2:
/etc/shorewall/macro.SMTP#TARGET SOURCE DEST PROTO DEST PORT(S)
PARAM - 192.168.1.5 tcp 25/etc/shorewall/rules#ACTION SOURCE DEST PROTO DEST PORT(S)
SMTP(DNAT):info net locThis would be equivalent to coding the following directly in
/etc/shorewall/rules#ACTION SOURCE DEST PROTO DEST PORT(S)
DNAT:info net loc:192.168.1.5 tcp 25
You may also specify SOURCE or DEST in the SOURCE and DEST
columns. This allows you to define macros that work in both
directions.Example 3:
/etc/shorewall/macro.SMBBI (Note: there
is already a standard macro like this released as part of
Shorewall):#ACTION SOURCE DEST PROTO DEST SOURCE ORIGINAL RATE USER/
# PORT PORT(S) DEST LIMIT GROUP
PARAM - - udp 135,445
PARAM - - udp 137:139
PARAM - - udp 1024: 137
PARAM - - tcp 135,139,445
PARAM DEST SOURCE udp 135,445
PARAM DEST SOURCE udp 137:139
PARAM DEST SOURCE udp 1024: 137
PARAM DEST SOURCE tcp 135,139,445
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE/etc/shorewall/rules:#ACTION SOURCE DEST PROTO DEST PORT(S)
SMBBI(ACCEPT) loc fwThis would be equivalent to coding the following directly in
/etc/shorewall/rules#ACTION SOURCE DEST PROTO DEST PORT(S)
ACCEPT loc fw udp 135,445
ACCEPT loc fw udp 137:139
ACCEPT loc fw udp 1024: 137
ACCEPT loc fw tcp 135,139,445
ACCEPT fw loc udp 135,445
ACCEPT fw loc udp 137:139
ACCEPT fw loc udp 1024: 137
ACCEPT fw loc tcp 135,139,445
Remaining columnsAny value in the invocation replaces the value in the rule in
the macro.One additional restriction should be noted: macros that are invoked
from actions cannot themselves invoke other actions.Defining your own MacrosTo define a new macro:Macro names must be valid shell variable names ((must begin with
a letter and be composed of letters, digits and underscore characters)
as well as valid Netfilter chain names.Copy /usr/share/shorewall/macro.template to
/etc/shorewall/macro.MacroName (for example, if
your new macro name is Foo then copy
/usr/share/shorewall/macro.template to
/etc/shorewall/macro.Foo).Now modify the new file to define the new macro.Shorewall 4.4.16 and LaterBeginning with Shorewall 4.4.16, the columns in macro.template are
the same as those in shorewall-rules (5). The first non-commentary line
in the template must beFORMAT 2There are no restrictions regarding the ACTIONs that can be
performed in a macro.Shorewall 4.4.15 and EarlierBefore 4.4.16, columns in the macro.template file were as
follows:ACTION - ACCEPT, DROP, REJECT, DNAT, DNAT-, REDIRECT,
CONTINUE, LOG, QUEUE, PARAM or an action name. Note that a macro may
not invoke another macro.ACCEPT - allow the connection requestACCEPT+ - like ACCEPT but also excludes the connection
from any subsequent DNAT[-] or REDIRECT[-] rules.NONAT - Excludes the connection from any subsequent
DNAT[-] or REDIRECT[-] rules but doesn't generate a rule to accept
the traffic.DROP - ignore the requestREJECT - disallow the request and return an icmp
unreachable or an RST packet.DNAT - Forward the request to another address (and
optionally another port).DNAT- - Advanced users only. Like DNAT but only generates
the DNAT iptables rule and not the companion ACCEPT rule.SAME - Similar to DNAT except that the port may not be
remapped and when multiple server addresses are listed, all
requests from a given remote system go to the same
server.SAME- - Advanced users only. Like SAME but only generates
the SAME iptables rule and not the companion ACCEPT rule.REDIRECT - Redirect the request to a local port on the
firewall.REDIRECT- - Advanced users only. Like REDIRECT but only
generates the REDIRECT iptables rule and not the companion ACCEPT
rule.CONTINUE - (For experts only). Do not process any of the
following rules for this (source zone,destination zone). If The
source and/or destination If the address falls into a zone defined
later in /etc/shorewall/zones, this connection request will be
passed to the rules defined for that (those) zone(s).LOG - Simply log the packet and continue.QUEUE - Queue the packet to a user-space application such
as ftwall (http://p2pwall.sf.net).The ACTION may optionally be followed by ":" and a syslog log
level (e.g, REJECT:info or DNAT:debug). This causes the packet to be
logged at the specified level.SOURCE - Source hosts to which the rule applies. A
comma-separated list of subnets and/or hosts. Hosts may be specified
by IP or MAC address; mac addresses must begin with ~
and must use - as a separator.Alternatively, clients may be specified by interface name. For
example, eth1 specifies a client that communicates with the firewall
system through eth1. This may be optionally followed by another
colon (:) and an IP/MAC/subnet address as described
above (e.g. eth1:192.168.1.5).May also contain 'DEST' as described above.DEST - Location of Server. Same as above with the exception
that MAC addresses are not allowed.Unlike in the SOURCE column, you may specify a range of up to
256 IP addresses using the syntax <first
ip>-<last ip>.May also contain 'SOURCE' as described above.PROTO - Protocol - Must be tcp,
udp, icmp, a number, or
all.DEST PORT(S) - Destination Ports. A comma-separated list of
Port names (from /etc/services), port numbers
or port ranges; if the protocol is icmp, this column
is interpreted as the destination icmp-type(s).A port range is expressed as <low
port>:<high port>.This column is ignored if PROTOCOL = all but must be entered
if any of the following fields are supplied. In that case, it is
suggested that this field contain -.If your kernel contains multi-port match support, then only a
single Netfilter rule will be generated if in this list and in the
CLIENT PORT(S) list below:There are 15 or less ports listed.No port ranges are included.Otherwise, a separate rule will be generated for each
port.SOURCE PORT(S) - Port(s) used by the client. If omitted, any
source port is acceptable. Specified as a comma-separated list of
port names, port numbers or port ranges.If you don't want to restrict client ports but need to specify
an ADDRESS in the next column, then place "-" in this column.If your kernel contains multi-port match support, then only a
single Netfilter rule will be generated if in this list and in the
DEST PORT(S) list above:There are 15 or less ports listed.No port ranges are included.Otherwise, a separate rule will be generated for each
port.ORIGINAL DEST (Shorewall-perl 4.2.0 and later)To use this column, you must include 'FORMAT 2' as the first
non-comment line in your macro file.If ACTION is DNAT[-] or REDIRECT[-] then if this column is
included and is different from the IP address given in the DEST
column, then connections destined for that address will be forwarded
to the IP and port specified in the DEST column.A comma-separated list of addresses may also be used. This is
most useful with the REDIRECT target where you want to redirect
traffic destined for particular set of hosts. Finally, if the list
of addresses begins with "!" (exclusion) then the rule will be
followed only if the original destination address in the connection
request does not match any of the addresses listed.For other actions, this column may be included and may contain
one or more addresses (host or network) separated by commas. Address
ranges are not allowed. When this column is supplied, rules are
generated that require that the original destination address matches
one of the listed addresses. This feature is most useful when you
want to generate a filter rule that corresponds to a DNAT- or
REDIRECT- rule. In this usage, the list of addresses should not
begin with "!".It is also possible to specify a set of addresses then exclude
part of those addresses. For example, 192.168.1.0/24!192.168.1.16/28
specifies the addresses 192.168.1.0-182.168.1.15 and
192.168.1.32-192.168.1.255. See shorewall-exclusion(5).See http://shorewall.net/PortKnocking.html
for an example of using an entry in this column with a user-defined
action rule.RATE LIMIT - You may rate-limit the rule by placing a value in
this column: <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> is
given, a value of 5 is assumed. There may be no whitespace embedded
in the specification. Example: 10/sec:20USER/GROUP - For output rules (those with the firewall as
their source), you may control connections based on the effective
UID and/or GID of the process requesting the connection. This column
can contain any of the following:[!]<user number>[:][!]<user name>[:][!]:<group number>[!]:<group name>[!]<user
number>:<group
number>[!]<user
name>:<group
number>[!]<user
inumber>:<group
name>[!]<user
name>:<group
name>[!]+<program name> (Note:
support for this form was removed from Netfilter in kernel version
2.6.14).MARK - (Added in Shorewall-4.4.2) Defines a test on the
existing packet or connection mark. The rule will match only if the
test returns true. Must be empty or '-' if the macro is to be used
within an action. [!]value[/mask][:C]!Inverts the test (not equal)valueValue of the packet or connection mark.maskA mask to be applied to the mark before testing.:CDesignates a connection mark. If omitted, the # packet
mark's value is tested.CONNLIMIT - (Added in Shorewall-4.4.2) Must be empty or '-' if
the macro is to be used within an action. [!]limit[:mask]May be used to limit the number of simultaneous connections
from each individual host to limit connections. Requires connlimit
match in your kernel and iptables. While the limit is only checked
on rules specifying CONNLIMIT, the number of current connections is
calculated over all current connections from the SOURCE host. By
default, the limit is applied to each
host but can be made to apply to networks of hosts by specifying a
mask. The mask specifies the width of a
VLSM mask to be applied to the source address; the number of current
connections is then taken over all hosts in the subnet
source-address/mask.
When ! is specified, the rule matches when the number of connection
exceeds the limit.TIME - (Added in Shorewall-4.4.2) Must be empty or '-' if the
macro is to be used within an action. <timeelement>[&...]timeelement may be:timestart=hh:mm[:ss]Defines the starting time of day.timestop=hh:mm[:ss]Defines the ending time of day.utcTimes are expressed in Greenwich Mean Time.localtzTimes are expressed in Local Civil Time
(default).weekdays=ddd[,ddd]...where ddd is one of
, ,
, ,
, or
monthdays=dd[,dd],...where dd is an ordinal day of
the monthdatestart=yyyy[-mm[-dd[hh[:mm[:ss]]]]]Defines the starting date and time.datestop=yyyy[-mm[-dd[hh[:mm[:ss]]]]]Defines the ending date and time.Omitted column entries should be entered using a dash
("-:).Example:/etc/shorewall/macro.LogAndAccept LOG:info
ACCEPTTo use your macro, in /etc/shorewall/rules
you might do something like:#ACTION SOURCE DEST PROTO DEST PORT(S)
LogAndAccept loc $FW tcp 22Macros and LoggingSpecifying a log level in a rule that invokes a user- or
Shorewall-defined action will cause each rule in the macro to be logged
with the specified level (and tag).The extent to which logging of macro rules occur is governed by the
following:When you invoke a macro and specify a log level, only those
rules in the macro that have no log level will be changed to log at
the level specified at the action invocation.Example:/etc/shorewall/macro.foo#ACTION SOURCE DEST PROTO DEST PORT(S)
ACCEPT - - tcp 22
bar:info/etc/shorewall/rules:#ACTION SOURCE DEST PROTO DEST PORT(S)
foo:debug $FW netLogging in the invoked 'foo' macro will be as if foo had been
defined as:#ACTION SOURCE DEST PROTO DEST PORT(S)
ACCEPT:debug - - tcp 22
bar:infoIf you follow the log level with "!" then logging will be at
that level for all rules recursively invoked by the macro.Example:/etc/shorewall/macro.foo#ACTION SOURCE DEST PROTO DEST PORT(S)
ACCEPT - - tcp 22
bar:info/etc/shorewall/rules:#ACTION SOURCE DEST PROTO DEST PORT(S)
foo:debug! $FW netLogging in the invoked 'foo' macro will be as if foo had been
defined as:#ACTION SOURCE DEST PROTO DEST PORT(S)
ACCEPT:debug - - tcp 22
bar:debugHow do I know if I should create an Action or a Macro?While actions and macros perform similar functions, in any given
case you will generally find that one is more appropriate than the
other.You can not associate an Extension Script with a macro the way that you can with an
Action. So if you need access to iptables features not
directly supported by Shorewall then you must use an action.Macros are expanded in-line while each action is its own chain.
So if there are a lot of rules involved in your new action/macro then
it is generally better to use an action than a macro. Only the packets
selected when you invoke the action are directed to the corresponding
chain. On the other hand, if there are only one or two rules involved
in what you want to do then a macro is more efficient.