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shorewall_code/Shorewall/manpages/shorewall-interfaces.xml
Tom Eastep b154803f22
Rename 'noanycast' to 'omitanycast' 
Signed-off-by: Tom Eastep <teastep@shorewall.net>
2020-09-10 09:59:45 -07:00

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
<refentry>
<refmeta>
<refentrytitle>shorewall-interfaces</refentrytitle>
<manvolnum>5</manvolnum>
<refmiscinfo>Configuration Files</refmiscinfo>
</refmeta>
<refnamediv>
<refname>interfaces</refname>
<refpurpose>Shorewall interfaces file</refpurpose>
</refnamediv>
<refsynopsisdiv>
<cmdsynopsis>
<command>/etc/shorewall[6]/interfaces</command>
</cmdsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>The interfaces file serves to define the firewall's network
interfaces to Shorewall. The order of entries in this file is not
significant in determining zone composition.</para>
<para>Beginning with Shorewall 4.5.3, the interfaces file supports two
different formats:</para>
<variablelist>
<varlistentry>
<term>FORMAT 1 (default - deprecated)</term>
<listitem>
<para>There is a BROADCAST column which can be used to specify the
broadcast address associated with the interface.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>FORMAT 2</term>
<listitem>
<para>The BROADCAST column is omitted.</para>
</listitem>
</varlistentry>
</variablelist>
<para>The format is specified by a line as follows:</para>
<blockquote>
<para><emphasis role="bold">?FORMAT {1|2}</emphasis></para>
</blockquote>
<para>The columns in the file are as follows.</para>
<variablelist>
<varlistentry>
<term><emphasis role="bold">ZONE</emphasis> -
<emphasis>zone-name</emphasis></term>
<listitem>
<para>Zone for this interface. Must match the name of a zone
declared in /etc/shorewall/zones. You may not list the firewall zone
in this column.</para>
<para>If the interface serves multiple zones that will be defined in
the <ulink url="shorewall-hosts.html">shorewall-hosts</ulink>(5)
file, you should place "-" in this column.</para>
<para>If there are multiple interfaces to the same zone, you must
list them in separate entries.</para>
<para>Example:</para>
<blockquote>
<programlisting>#ZONE INTERFACE BROADCAST
loc eth1 -
loc eth2 -</programlisting>
</blockquote>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">INTERFACE</emphasis> -
<emphasis>interface</emphasis><emphasis
role="bold">[:</emphasis><emphasis>port</emphasis><emphasis
role="bold">]</emphasis></term>
<listitem>
<para>Logical name of interface. Each interface may be listed only
once in this file. You may NOT specify the name of a "virtual"
interface (e.g., eth0:0) here; see <ulink
url="../FAQ.htm#faq18">https://shorewall.org/FAQ.htm#faq18</ulink>.
If the <option>physical</option> option is not specified, then the
logical name is also the name of the actual interface.</para>
<para>You may use wildcards here by specifying a prefix followed by
the plus sign ("+"). For example, if you want to make an entry that
applies to all PPP interfaces, use 'ppp+'; that would match ppp0,
ppp1, ppp2, …</para>
<para>When using Shorewall versions before 4.1.4, care must be
exercised when using wildcards where there is another zone that uses
a matching specific interface. See <ulink
url="shorewall-nesting.html">shorewall-nesting</ulink>(5) for a
discussion of this problem.</para>
<para>Shorewall allows '+' as an interface name, but that usage is
deprecated. A better approach is to specify
'<option>physical</option>=+' in the OPTIONS column (see
below).</para>
<para>There is no need to define the loopback interface (lo) in this
file.</para>
<para>If a <replaceable>port</replaceable> is given, then the
<replaceable>interface</replaceable> must have been defined
previously with the <option>bridge</option> option. The OPTIONS
column may not contain the following options when a
<replaceable>port</replaceable> is given.</para>
<simplelist>
<member>arp_filter</member>
<member>arp_ignore</member>
<member>bridge</member>
<member>log_martians</member>
<member>mss</member>
<member>optional</member>
<member>proxyarp</member>
<member>required</member>
<member>routefilter</member>
<member>sourceroute</member>
<member>upnp</member>
<member>wait</member>
</simplelist>
<para>Beginning with Shorewall 4.5.17, if you specify a zone for the
'lo' interface, then that zone must be defined as type
<option>local</option> in <ulink
url="shorewall-zones.html">shorewall6-zones</ulink>(5).</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">BROADCAST</emphasis> (Optional) -
{<emphasis role="bold">-</emphasis>|<emphasis
role="bold">detect</emphasis>|<emphasis>address</emphasis>[,<emphasis>address</emphasis>]...}</term>
<listitem>
<para>Only available if FORMAT 1.</para>
<para>If you use the special value <emphasis
role="bold">detect</emphasis>, Shorewall will detect the broadcast
address(es) for you if your iptables and kernel include Address Type
Match support.</para>
<para>If your iptables and/or kernel lack Address Type Match support
then you may list the broadcast address(es) for the network(s) to
which the interface belongs. For P-T-P interfaces, this column is
left blank. If the interface has multiple addresses on multiple
subnets then list the broadcast addresses as a comma-separated
list.</para>
<para>If you don't want to give a value for this column but you want
to enter a value in the OPTIONS column, enter <emphasis
role="bold">-</emphasis> in this column.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">OPTIONS</emphasis> (Optional) -
[<emphasis>option</emphasis>[<emphasis
role="bold">,</emphasis><emphasis>option</emphasis>]...]</term>
<listitem>
<para>A comma-separated list of options from the following list. The
order in which you list the options is not significant but the list
should have no embedded white-space.</para>
<variablelist>
<varlistentry>
<term><emphasis
role="bold">accept_ra</emphasis>[={0|1|2}]</term>
<listitem>
<para>IPv6 only; added in Shorewall 4.5.16. Values are:</para>
<variablelist>
<varlistentry>
<term>0</term>
<listitem>
<para>Do not accept Router Advertisements.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>1</term>
<listitem>
<para>Accept Route Advertisements if forwarding is
disabled.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>2</term>
<listitem>
<para>Overrule forwarding behavior. Accept Route
Advertisements even if forwarding is enabled.</para>
</listitem>
</varlistentry>
</variablelist>
<para>If the option is specified without a value, then the
value 1 is assumed.</para>
<note>
<para>This option does not work with a wild-card <emphasis
role="bold">physical</emphasis> name (e.g., eth0.+).
Beginning with Shorewall 5.1.10, If this option is
specified, a warning is issued and the option is
ignored.</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">arp_filter[={0|1}]</emphasis></term>
<listitem>
<para>IPv4 only. If specified, this interface will only
respond to ARP who-has requests for IP addresses configured on
the interface. If not specified, the interface can respond to
ARP who-has requests for IP addresses on any of the firewall's
interface. The interface must be up when Shorewall is
started.</para>
<para>Only those interfaces with the
<option>arp_filter</option> option will have their setting
changed; the value assigned to the setting will be the value
specified (if any) or 1 if no value is given.</para>
<note>
<para>This option does not work with a wild-card <emphasis
role="bold">physical</emphasis> name (e.g., eth0.+).
Beginning with Shorewall 5.1.10, If this option is
specified, a warning is issued and the option is
ignored.</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis
role="bold">arp_ignore</emphasis>[=<emphasis>number</emphasis>]</term>
<listitem>
<para>IPv4 only. If specified, this interface will respond to
arp requests based on the value of <emphasis>number</emphasis>
(defaults to 1).</para>
<para>1 - reply only if the target IP address is local address
configured on the incoming interface</para>
<para>2 - reply only if the target IP address is local address
configured on the incoming interface and the sender's IP
address is part from same subnet on this interface's
address</para>
<para>3 - do not reply for local addresses configured with
scope host, only resolutions for global and link</para>
<para>4-7 - reserved</para>
<para>8 - do not reply for all local addresses</para>
<note>
<para>This option does not work with a wild-card <emphasis
role="bold">physical</emphasis> name (e.g., eth0.+).
Beginning with Shorewall 5.1.10, If this option is
specified, a warning is issued and the option is
ignored.</para>
</note>
<warning>
<para>Do not specify <emphasis
role="bold">arp_ignore</emphasis> for any interface involved
in <ulink url="../ProxyARP.htm">Proxy ARP</ulink>.</para>
</warning>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">blacklist</emphasis></term>
<listitem>
<para>Checks packets arriving on this interface against the
<ulink
url="shorewall-blacklist.html">shorewall-blacklist</ulink>(5)
file.</para>
<para>Beginning with Shorewall 4.4.13:</para>
<itemizedlist>
<listitem>
<para>If a <replaceable>zone</replaceable> is given in the
ZONES column, then the behavior is as if <emphasis
role="bold">blacklist</emphasis> had been specified in the
IN_OPTIONS column of <ulink
url="shorewall-zones.html">shorewall-zones</ulink>(5).</para>
</listitem>
<listitem>
<para>Otherwise, the option is ignored with a
warning:</para>
<blockquote>
<para><emphasis role="bold">WARNING: The 'blacklist'
option is ignored on multi-zone
interfaces</emphasis></para>
</blockquote>
</listitem>
</itemizedlist>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">bridge</emphasis></term>
<listitem>
<para>Designates the interface as a bridge. Beginning with
Shorewall 4.4.7, setting this option also sets
<option>routeback</option>.</para>
<note>
<para>If you have a bridge that you don't intend to define
bport zones on, then it is best to omit this option and
simply specify <option>routeback</option>.</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis
role="bold">dbl={none|src|dst|src-dst}</emphasis></term>
<listitem>
<para>Added in Shorewall 5.0.10. This option defined whether
or not dynamic blacklisting is applied to packets entering the
firewall through this interface and whether the source address
and/or destination address is to be compared against the
ipset-based dynamic blacklist (DYNAMIC_BLACKLIST=ipset... in
<ulink url="shorewall.conf.html">shorewall.conf(5)</ulink>).
The default is determine by the setting of
DYNAMIC_BLACKLIST:</para>
<variablelist>
<varlistentry>
<term>DYNAMIC_BLACKLIST=No</term>
<listitem>
<para>Default is <emphasis role="bold">none</emphasis>
(e.g., no dynamic blacklist checking).</para>
</listitem>
</varlistentry>
<varlistentry>
<term>DYNAMIC_BLACKLIST=Yes</term>
<listitem>
<para>Default is <emphasis role="bold">src</emphasis>
(e.g., the source IP address is checked).</para>
</listitem>
</varlistentry>
<varlistentry>
<term>DYNAMIC_BLACKLIST=ipset[-only]</term>
<listitem>
<para>Default is <emphasis
role="bold">src</emphasis>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>DYNAMIC_BLACKLIST=ipset[-only],src-dst...</term>
<listitem>
<para>Default is <emphasis
role="bold">src-dst</emphasis> (e.g., the source IP
addresses in checked against the ipset on input and the
destination IP address is checked against the ipset on
packets originating from the firewall and leaving
through this interface).</para>
</listitem>
</varlistentry>
</variablelist>
<para>The normal setting for this option will be <emphasis
role="bold">dst</emphasis> or <emphasis
role="bold">none</emphasis> for internal interfaces and
<emphasis role="bold">src</emphasis> or <emphasis
role="bold">src-dst</emphasis> for Internet-facing
interfaces.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">destonly</emphasis></term>
<listitem>
<para>Added in Shorewall 4.5.17. Causes the compiler to omit
rules to handle traffic from this interface.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">dhcp</emphasis></term>
<listitem>
<para>Specify this option when any of the following are
true:</para>
<orderedlist spacing="compact">
<listitem>
<para>the interface gets its IP address via DHCP</para>
</listitem>
<listitem>
<para>the interface is used by a DHCP server running on
the firewall</para>
</listitem>
<listitem>
<para>the interface has a static IP but is on a LAN
segment with lots of DHCP clients.</para>
</listitem>
<listitem>
<para>the interface is a <ulink
url="../SimpleBridge.html">simple bridge</ulink> with a
DHCP server on one port and DHCP clients on another
port.</para>
<note>
<para>If you use <ulink
url="../bridge-Shorewall-perl.html">Shorewall-perl for
firewall/bridging</ulink>, then you need to include
DHCP-specific rules in <ulink
url="shorewall-rules.html">shorewall-rules</ulink>(5).
DHCP uses UDP ports 67 and 68.</para>
</note>
</listitem>
</orderedlist>
<para>This option allows DHCP datagrams to enter and leave the
interface.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">forward</emphasis>[={0|1}]</term>
<listitem>
<para>IPv6 only Sets the
/proc/sys/net/ipv6/conf/interface/forwarding option to the
specified value. If no value is supplied, then 1 is
assumed.</para>
<note>
<para>This option does not work with a wild-card <emphasis
role="bold">physical</emphasis> name (e.g., eth0.+).
Beginning with Shorewall 5.1.10, If this option is
specified, a warning is issued and the option is
ignored.</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">ignore[=1]</emphasis></term>
<listitem>
<para>When specified, causes the generated script to ignore
up/down events from Shorewall-init for this device.
Additionally, the option exempts the interface from hairpin
filtering. When '=1' is omitted, the ZONE column must contain
'-' and <option>ignore</option> must be the only
OPTION.</para>
<para>Beginning with Shorewall 4.5.5, may be specified as
'<option>ignore=1</option>' which only causes the generated
script to ignore up/down events from Shorewall-init; hairpin
filtering is still applied. In this case, the above
restrictions on the ZONE and OPTIONS columns are
lifted.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">loopback</emphasis></term>
<listitem>
<para>Added in Shorewall 4.6.6. Designates the interface as
the loopback interface. This option is assumed if the
interface's physical name is 'lo'. Only one interface man have
the <option>loopback</option> option specified.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis
role="bold">logmartians[={0|1}]</emphasis></term>
<listitem>
<para>IPv4 only. Turn on kernel martian logging (logging of
packets with impossible source addresses. It is strongly
suggested that if you set <emphasis
role="bold">routefilter</emphasis> on an interface that you
also set <emphasis role="bold">logmartians</emphasis>. Even if
you do not specify the <option>routefilter</option> option, it
is a good idea to specify <option>logmartians</option> because
your distribution may have enabled route filtering without you
knowing it.</para>
<para>Only those interfaces with the
<option>logmartians</option> option will have their setting
changed; the value assigned to the setting will be the value
specified (if any) or 1 if no value is given.</para>
<para>To find out if route filtering is set on a given
<replaceable>interface</replaceable>, check the contents of
<filename>/proc/sys/net/ipv4/conf/<replaceable>interface</replaceable>/rp_filter</filename>
- a non-zero value indicates that route filtering is
enabled.</para>
<para>Example:</para>
<programlisting> teastep@lists:~$ <command>cat /proc/sys/net/ipv4/conf/eth0/rp_filter </command>
1
teastep@lists:~$ </programlisting>
<para/>
<note>
<para>This option does not work with a wild-card <emphasis
role="bold">physical</emphasis> name (e.g., eth0.+).
Beginning with Shorewall 5.1.10, If this option is
specified, a warning is issued and the option is
ignored.</para>
</note>
<blockquote>
<para>This option may also be enabled globally in the <ulink
url="shorewall.conf.html">shorewall.conf</ulink>(5)
file.</para>
</blockquote>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">maclist</emphasis></term>
<listitem>
<para>Connection requests from this interface are compared
against the contents of <ulink
url="shorewall-maclist.html">shorewall-maclist</ulink>(5). If
this option is specified, the interface must be an Ethernet
NIC and must be up before Shorewall is started.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold"><emphasis
role="bold">mss</emphasis>=</emphasis><emphasis>number</emphasis></term>
<listitem>
<para>Added in Shorewall 4.0.3. Causes forwarded TCP SYN
packets entering or leaving on this interface to have their
MSS field set to the specified
<replaceable>number</replaceable>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis
role="bold">nets=(<emphasis>net</emphasis>[,...])</emphasis></term>
<listitem>
<para>Limit the zone named in the ZONE column to only the
listed networks. The parentheses may be omitted if only a
single <replaceable>net</replaceable> is given (e.g.,
nets=192.168.1.0/24). Limited broadcast to the zone is
supported. Beginning with Shorewall 4.4.1, multicast traffic
to the zone is also supported.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">nets=dynamic</emphasis></term>
<listitem>
<para>Defines the zone as <firstterm>dynamic</firstterm>.
Requires ipset match support in your iptables and kernel. See
<ulink
url="../Dynamic.html">https://shorewall.org/Dynamic.html</ulink>
for further information.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">nodbl</emphasis></term>
<listitem>
<para>Added in Shorewall 5.0.8. When specified, dynamic
blacklisting is disabled on the interface. Beginning with
Shorewall 5.0.10, <emphasis role="bold">nodbl</emphasis> is
equivalent to <emphasis
role="bold">dbl=none</emphasis>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">nosmurfs</emphasis></term>
<listitem>
<para>IPv4 only. Filter packets for smurfs (packets with a
broadcast address as the source).</para>
<para>Smurfs will be optionally logged based on the setting of
SMURF_LOG_LEVEL in <ulink
url="shorewall.conf.html">shorewall.conf</ulink>(5). After
logging, the packets are dropped.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>omitanycast</term>
<listitem>
<para>IPv6 only. Added in Shorewall 5.2.8.</para>
<para>Shorewall6 has traditionally generated rules for IPv6
<emphasis>anycast</emphasis> addresses. These rules
include:</para>
<orderedlist numeration="loweralpha">
<listitem>
<para>Packets with these destination IP addresses are
dropped by REJECT rules.</para>
</listitem>
<listitem>
<para>Packets with these source IP addresses are dropped
by the 'nosmurfs' interface option and by the 'dropSmurfs'
action.</para>
</listitem>
<listitem>
<para>Packets with these destination IP addresses are not
logged during policy enforcement.</para>
</listitem>
<listitem>
<para>Packets with these destination IP addresses are
processes by the 'Broadcast' action.</para>
</listitem>
</orderedlist>
<para>This can be inhibited for individual interfaces by
specifying <emphasis role="bold">noanycast</emphasis> for
those interfaces.</para>
<note>
<para>RFC 2526 describes IPv6 subnet anycast addresses. The
RFC makes a distinction between subnets with "IPv6 address
types required to have 64-bit interface identifiers in
EUI-64 format" and all other subnets. When generating these
anycast addresses, the Shorewall compiler does not make this
distinction and unconditionally assumes that the last 128
addresses in the subnet are reserved as anycast
addresses.</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">optional</emphasis></term>
<listitem>
<para>This option indicates that the firewall should be able
to start, even if the interface is not usable for handling
traffic. It allows use of the <command>enable</command> and
<command>disable</command> commands on the interface.</para>
<para>When <option>optional</option> is specified for an
interface, Shorewall will be silent when:</para>
<itemizedlist>
<listitem>
<para>a <filename
class="directory">/proc/sys/net/ipv[46]/conf/</filename>
entry for the interface cannot be modified (including for
proxy ARP or proxy NDP).</para>
</listitem>
<listitem>
<para>The first address of the interface cannot be
obtained.</para>
</listitem>
<listitem>
<para>The gateway of the interface can not be obtained
(provider interface).</para>
</listitem>
<listitem>
<para>The interface has been disabled using the
<command>disable</command> command.</para>
</listitem>
</itemizedlist>
<para>May not be specified with <emphasis
role="bold">required</emphasis>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">physical</emphasis>=<emphasis
role="bold"><emphasis>name</emphasis></emphasis></term>
<listitem>
<para>Added in Shorewall 4.4.4. When specified, the interface
or port name in the INTERFACE column is a logical name that
refers to the name given in this option. It is useful when you
want to specify the same wildcard port name on two or more
bridges. See <ulink
url="../bridge-Shorewall-perl.html#Multiple">https://shorewall.org/bridge-Shorewall-perl.html#Multiple</ulink>.</para>
<para>If the <emphasis>interface</emphasis> name is a wildcard
name (ends with '+'), then the physical
<emphasis>name</emphasis> must also end in '+'. The physical
<replaceable>name</replaceable> may end in '+' (or be exactly
'+') when the <replaceable>interface</replaceable> name is not
a wildcard name.</para>
<para>If <option>physical</option> is not specified, then it's
value defaults to the <emphasis>interface</emphasis>
name.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">proxyarp[={0|1}]</emphasis></term>
<listitem>
<para>IPv4 only. Sets
/proc/sys/net/ipv4/conf/<emphasis>interface</emphasis>/proxy_arp.
Do NOT use this option if you are employing Proxy ARP through
entries in <ulink
url="shorewall-proxyarp.html">shorewall-proxyarp</ulink>(5).
This option is intended solely for use with Proxy ARP
sub-networking as described at: <ulink
url="http://tldp.org/HOWTO/Proxy-ARP-Subnet/index.html">http://tldp.org/HOWTO/Proxy-ARP-Subnet/index.html.
</ulink></para>
<note>
<para>This option does not work with a wild-card <emphasis
role="bold">physical</emphasis> name (e.g., eth0.+).
Beginning with Shorewall 5.1.10, If this option is
specified, a warning is issued and the option is
ignored.</para>
</note>
<para>Only those interfaces with the <option>proxyarp</option>
option will have their setting changed; the value assigned to
the setting will be the value specified (if any) or 1 if no
value is given.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">proxyndp</emphasis>[={0|1}]</term>
<listitem>
<para>IPv6 only. Sets
/proc/sys/net/ipv6/conf/<emphasis>interface</emphasis>/proxy_ndp.</para>
<note>
<para>This option does not work with a wild-card <emphasis
role="bold">physical</emphasis> name (e.g., eth0.+).
Beginning with Shorewall 5.1.10, If this option is
specified, a warning is issued and the option is
ignored.</para>
</note>
<para>Only those interfaces with the <option>proxyndp</option>
option will have their setting changed; the value assigned to
the setting will be the value specified (if any) or 1 if no
value is given.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">required</emphasis></term>
<listitem>
<para>Added in Shorewall 4.4.10. If this option is set, the
firewall will fail to start if the interface is not usable.
May not be specified together with <emphasis
role="bold">optional</emphasis>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">routeback[={0|1}]</emphasis></term>
<listitem>
<para>If specified, indicates that Shorewall should include
rules that allow traffic arriving on this interface to be
routed back out that same interface. This option is also
required when you have used a wildcard in the INTERFACE column
if you want to allow traffic between the interfaces that match
the wildcard.</para>
<para>Beginning with Shorewall 4.4.20, if you specify this
option, then you should also specify either
<option>sfilter</option> (see below) or
<option>routefilter</option> on all interfaces (see
below).</para>
<para>Beginning with Shorewall 4.5.18, you may specify this
option to explicitly reset (e.g., <emphasis
role="bold">routeback=0</emphasis>). This can be used to
override Shorewall's default setting for bridge devices which
is <emphasis role="bold">routeback=1</emphasis>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis
role="bold">routefilter[={0|1|2}]</emphasis></term>
<listitem>
<para>IPv4 only. Turn on kernel route filtering for this
interface (anti-spoofing measure).</para>
<para>Only those interfaces with the
<option>routefilter</option> option will have their setting
changes; the value assigned to the setting will be the value
specified (if any) or 1 if no value is given.</para>
<para>The value 2 is only available with Shorewall 4.4.5.1 and
later when the kernel version is 2.6.31 or later. It specifies
a <firstterm>loose</firstterm> form of reverse path
filtering.</para>
<note>
<para>This option does not work with a wild-card <emphasis
role="bold">physical</emphasis> name (e.g., eth0.+).
Beginning with Shorewall 5.1.10, If this option is
specified, a warning is issued and the option is
ignored.</para>
</note>
<para>This option can also be enabled globally via the
ROUTE_FILTER option in the <ulink
url="shorewall.conf.html">shorewall.conf</ulink>(5)
file.</para>
<important>
<para>If ROUTE_FILTER=Yes in <ulink
url="shorewall.conf.html">shorewall.conf</ulink>(5), or if
your distribution sets net.ipv4.conf.all.rp_filter=1 in
<filename>/etc/sysctl.conf</filename>, then setting
<emphasis role="bold">routefilter</emphasis>=0 in an
<replaceable>interface</replaceable> entry will not disable
route filtering on that
<replaceable>interface</replaceable>! The effective setting
for an <replaceable>interface</replaceable> is the maximum
of the contents of
<filename>/proc/sys/net/ipv4/conf/all/rp_filter</filename>
and the routefilter setting specified in this file
(/proc/sys/net/ipv4/conf/<replaceable>interface</replaceable>/rp_filter).</para>
</important>
<note>
<para>There are certain cases where
<option>routefilter</option> cannot be used on an
interface:</para>
<itemizedlist>
<listitem>
<para>If USE_DEFAULT_RT=Yes in <ulink
url="shorewall.conf.html">shorewall.conf</ulink>(5) and
the interface is listed in <ulink
url="shorewall-providers.html">shorewall-providers</ulink>(5).</para>
</listitem>
<listitem>
<para>If there is an entry for the interface in <ulink
url="shorewall-providers.html">shorewall-providers</ulink>(5)
that doesn't specify the <option>balance</option>
option.</para>
</listitem>
<listitem>
<para>If IPSEC is used to allow a road-warrior to have a
local address, then any interface through which the
road-warrior might connect cannot specify
<option>routefilter</option>.</para>
</listitem>
</itemizedlist>
</note>
<para>Beginning with Shorewall 5.1.1, when
<option>routefilter</option> is set to a non-zero value, the
<option>logmartians</option> option is also implicitly set. If
you actually want route filtering without logging, then you
must also specify <option>logmartians=0</option> after
<option>routefilter</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">rpfilter</emphasis></term>
<listitem>
<para>Added in Shorewall 4.5.7. This is an anti-spoofing
measure that requires the 'RPFilter Match' capability in your
iptables and kernel. It provides a more efficient alternative
to the <option>sfilter</option> option below. It performs a
function similar to <option>routefilter</option> (see above)
but works with Multi-ISP configurations that do not use
balanced routes.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis
role="bold">sfilter=(<emphasis>net</emphasis>[,...])</emphasis></term>
<listitem>
<para>Added in Shorewall 4.4.20. This option provides an
anti-spoofing alternative to <option>routefilter</option> on
interfaces where that option cannot be used, but where the
<option>routeback</option> option is required (on a bridge,
for example). On these interfaces, <option>sfilter</option>
should list those local networks that are connected to the
firewall through other interfaces.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis
role="bold">sourceroute[={0|1}]</emphasis></term>
<listitem>
<para>If this option is not specified for an interface, then
source-routed packets will not be accepted from that interface
unless it has been explicitly enabled via sysconf. Only set
this option to 1 (enable source routing) if you know what you
are doing. This might represent a security risk and is usually
unneeded.</para>
<para>Only those interfaces with the
<option>sourceroute</option> option will have their setting
changed; the value assigned to the setting will be the value
specified (if any) or 1 if no value is given.</para>
<note>
<para>This option does not work with a wild-card <emphasis
role="bold">physical</emphasis> name (e.g., eth0.+).
Beginning with Shorewall 5.1.10, If this option is
specified, a warning is issued and the option is
ignored.</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">tcpflags[={0|1}]</emphasis></term>
<listitem>
<para>Packets arriving on this interface are checked for
certain illegal combinations of TCP flags. Packets found to
have such a combination of flags are handled according to the
setting of TCP_FLAGS_DISPOSITION after having been logged
according to the setting of TCP_FLAGS_LOG_LEVEL.</para>
<para>Beginning with Shorewall 4.6.0, tcpflags=1 is the
default. To disable this option, specify tcpflags=0.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">unmanaged</emphasis></term>
<listitem>
<para>Added in Shorewall 4.5.18. Causes all traffic between
the firewall and hosts on the interface to be accepted. When
this option is given:</para>
<itemizedlist>
<listitem>
<para>The ZONE column must contain '-'.</para>
</listitem>
<listitem>
<para>Only the following other options are allowed with
<emphasis role="bold">unmanaged</emphasis>:</para>
<simplelist>
<member><emphasis
role="bold">arp_filter</emphasis></member>
<member><emphasis
role="bold">arp_ignore</emphasis></member>
<member><emphasis role="bold">ignore</emphasis></member>
<member><emphasis
role="bold">routefilter</emphasis></member>
<member><emphasis
role="bold">optional</emphasis></member>
<member><emphasis
role="bold">physical</emphasis></member>
<member><emphasis
role="bold">routefilter</emphasis></member>
<member><emphasis
role="bold">proxyarp</emphasis></member>
<member><emphasis
role="bold">proxyudp</emphasis></member>
<member><emphasis
role="bold">sourceroute</emphasis></member>
</simplelist>
</listitem>
</itemizedlist>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">upnp</emphasis></term>
<listitem>
<para>Incoming requests from this interface may be remapped
via UPNP (upnpd). See <ulink
url="../UPnP.html">https://shorewall.org/UPnP.html</ulink>.
Supported in IPv4 and in IPv6 in Shorewall 5.1.4 and
later.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">upnpclient</emphasis></term>
<listitem>
<para>This option is intended for laptop users who always run
Shorewall on their system yet need to run UPnP-enabled client
apps such as Transmission (BitTorrent client). The option
causes Shorewall to detect the default gateway through the
interface and to accept UDP packets from that gateway. Note
that, like all aspects of UPnP, this is a security hole so use
this option at your own risk. Supported in IPv4 and in IPv6 in
Shorewall 5.1.4 and later.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis
role="bold">wait</emphasis>=<emphasis>seconds</emphasis></term>
<listitem>
<para>Added in Shorewall 4.4.10. Causes the generated script
to wait up to <emphasis>seconds</emphasis> seconds for the
interface to become usable before applying the <emphasis
role="bold">required</emphasis> or <emphasis
role="bold">optional</emphasis> options.</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Example</title>
<variablelist>
<varlistentry>
<term>IPv4 Example 1:</term>
<listitem>
<para>Suppose you have eth0 connected to a DSL modem and eth1
connected to your local network and that your local subnet is
192.168.1.0/24. The interface gets its IP address via DHCP from
subnet 206.191.149.192/27. You have a DMZ with subnet 192.168.2.0/24
using eth2. Your iptables and/or kernel do not support "Address Type
Match" and you prefer to specify broadcast addresses explicitly
rather than having Shorewall detect them.</para>
<para>Your entries for this setup would look like:</para>
<programlisting>?FORMAT 1
#ZONE INTERFACE BROADCAST OPTIONS
net eth0 206.191.149.223 dhcp
loc eth1 192.168.1.255
dmz eth2 192.168.2.255</programlisting>
</listitem>
</varlistentry>
<varlistentry>
<term>Example 2:</term>
<listitem>
<para>The same configuration without specifying broadcast addresses
is:</para>
<programlisting>?FORMAT 2
#ZONE INTERFACE OPTIONS
net eth0 dhcp
loc eth1
dmz eth2</programlisting>
</listitem>
</varlistentry>
<varlistentry>
<term>Example 3:</term>
<listitem>
<para>You have a simple dial-in system with no Ethernet
connections.</para>
<programlisting>?FORMAT 2
#ZONE INTERFACE OPTIONS
net ppp0 -</programlisting>
</listitem>
</varlistentry>
<varlistentry>
<term>Example 4 (Shorewall 4.4.9 and later):</term>
<listitem>
<para>You have a bridge with no IP address and you want to allow
traffic through the bridge.</para>
<programlisting>?FORMAT 2
#ZONE INTERFACE OPTIONS
- br0 bridge</programlisting>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>FILES</title>
<para>/etc/shorewall/interfaces</para>
<para>/etc/shorewall6/interfaces</para>
</refsect1>
<refsect1>
<title>See ALSO</title>
<para><ulink
url="../configuration_file_basics.htm#Pairs">https://shorewall.org/configuration_file_basics.htm#Pairs</ulink></para>
<para>shorewall(8)</para>
</refsect1>
</refentry>
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