Provided by: shorewall_5.2.8-6_all 
NAME
interfaces - Shorewall interfaces file
SYNOPSIS
/etc/shorewall[6]/interfaces
DESCRIPTION
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.
Beginning with Shorewall 4.5.3, the interfaces file supports two different formats:
FORMAT 1 (default - deprecated)
There is a BROADCAST column which can be used to specify the broadcast address
associated with the interface.
FORMAT 2
The BROADCAST column is omitted.
The format is specified by a line as follows:
?FORMAT {1|2}
The columns in the file are as follows.
ZONE - zone-name
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.
If the interface serves multiple zones that will be defined in the
shorewall-hosts[1](5) file, you should place "-" in this column.
If there are multiple interfaces to the same zone, you must list them in separate
entries.
Example:
#ZONE INTERFACE BROADCAST
loc eth1 -
loc eth2 -
INTERFACE - interface[:port]
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
https://shorewall.org/FAQ.htm#faq18[2]. If the physical option is not specified, then
the logical name is also the name of the actual interface.
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, ...
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
shorewall-nesting[3](5) for a discussion of this problem.
Shorewall allows '+' as an interface name, but that usage is deprecated. A better
approach is to specify 'physical=+' in the OPTIONS column (see below).
There is no need to define the loopback interface (lo) in this file.
If a port is given, then the interface must have been defined previously with the
bridge option. The OPTIONS column may not contain the following options when a port is
given.
arp_filter
arp_ignore
bridge
log_martians
mss
optional
proxyarp
required
routefilter
sourceroute
upnp
wait
Beginning with Shorewall 4.5.17, if you specify a zone for the 'lo' interface, then
that zone must be defined as type local in shorewall6-zones[4](5).
BROADCAST (Optional) - {-|detect|address[,address]...}
Only available if FORMAT 1.
If you use the special value detect, Shorewall will detect the broadcast address(es)
for you if your iptables and kernel include Address Type Match support.
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.
If you don't want to give a value for this column but you want to enter a value in the
OPTIONS column, enter - in this column.
OPTIONS (Optional) - [option[,option]...]
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.
accept_ra[={0|1|2}]
IPv6 only; added in Shorewall 4.5.16. Values are:
0
Do not accept Router Advertisements.
1
Accept Route Advertisements if forwarding is disabled.
2
Overrule forwarding behavior. Accept Route Advertisements even if forwarding
is enabled.
If the option is specified without a value, then the value 1 is assumed.
Note
This option does not work with a wild-card physical name (e.g., eth0.+).
Beginning with Shorewall 5.1.10, If this option is specified, a warning is
issued and the option is ignored.
arp_filter[={0|1}]
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.
Only those interfaces with the arp_filter 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.
Note
This option does not work with a wild-card physical name (e.g., eth0.+).
Beginning with Shorewall 5.1.10, If this option is specified, a warning is
issued and the option is ignored.
arp_ignore[=number]
IPv4 only. If specified, this interface will respond to arp requests based on the
value of number (defaults to 1).
1 - reply only if the target IP address is local address configured on the
incoming interface
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
3 - do not reply for local addresses configured with scope host, only resolutions
for global and link
4-7 - reserved
8 - do not reply for all local addresses
Note
This option does not work with a wild-card physical name (e.g., eth0.+).
Beginning with Shorewall 5.1.10, If this option is specified, a warning is
issued and the option is ignored.
Warning
Do not specify arp_ignore for any interface involved in Proxy ARP[5].
blacklist
Checks packets arriving on this interface against the shorewall-blacklist[6](5)
file.
Beginning with Shorewall 4.4.13:
• If a zone is given in the ZONES column, then the behavior is as if blacklist
had been specified in the IN_OPTIONS column of shorewall-zones[4](5).
• Otherwise, the option is ignored with a warning: WARNING: The 'blacklist'
option is ignored on multi-zone interfaces
bridge
Designates the interface as a bridge. Beginning with Shorewall 4.4.7, setting this
option also sets routeback.
Note
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 routeback.
dbl={none|src|dst|src-dst}
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
shorewall.conf(5)[7]). The default is determine by the setting of
DYNAMIC_BLACKLIST:
DYNAMIC_BLACKLIST=No
Default is none (e.g., no dynamic blacklist checking).
DYNAMIC_BLACKLIST=Yes
Default is src (e.g., the source IP address is checked).
DYNAMIC_BLACKLIST=ipset[-only]
Default is src.
DYNAMIC_BLACKLIST=ipset[-only],src-dst...
Default is src-dst (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).
The normal setting for this option will be dst or none for internal interfaces and
src or src-dst for Internet-facing interfaces.
destonly
Added in Shorewall 4.5.17. Causes the compiler to omit rules to handle traffic
from this interface.
dhcp
Specify this option when any of the following are true:
1. the interface gets its IP address via DHCP
2. the interface is used by a DHCP server running on the firewall
3. the interface has a static IP but is on a LAN segment with lots of DHCP
clients.
4. the interface is a simple bridge[8] with a DHCP server on one port and DHCP
clients on another port.
Note
If you use Shorewall-perl for firewall/bridging[9], then you need to
include DHCP-specific rules in shorewall-rules[10](5). DHCP uses UDP ports
67 and 68.
This option allows DHCP datagrams to enter and leave the interface.
forward[={0|1}]
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.
Note
This option does not work with a wild-card physical name (e.g., eth0.+).
Beginning with Shorewall 5.1.10, If this option is specified, a warning is
issued and the option is ignored.
ignore[=1]
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
ignore must be the only OPTION.
Beginning with Shorewall 4.5.5, may be specified as 'ignore=1' 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.
loopback
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 loopback option specified.
logmartians[={0|1}]
IPv4 only. Turn on kernel martian logging (logging of packets with impossible
source addresses. It is strongly suggested that if you set routefilter on an
interface that you also set logmartians. Even if you do not specify the
routefilter option, it is a good idea to specify logmartians because your
distribution may have enabled route filtering without you knowing it.
Only those interfaces with the logmartians 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.
To find out if route filtering is set on a given interface, check the contents of
/proc/sys/net/ipv4/conf/interface/rp_filter - a non-zero value indicates that
route filtering is enabled.
Example:
teastep@lists:~$ cat /proc/sys/net/ipv4/conf/eth0/rp_filter
1
teastep@lists:~$
Note
This option does not work with a wild-card physical name (e.g., eth0.+).
Beginning with Shorewall 5.1.10, If this option is specified, a warning is
issued and the option is ignored.
This option may also be enabled globally in the shorewall.conf[7](5) file.
maclist
Connection requests from this interface are compared against the contents of
shorewall-maclist[11](5). If this option is specified, the interface must be an
Ethernet NIC and must be up before Shorewall is started.
mss=number
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 number.
nets=(net[,...])
Limit the zone named in the ZONE column to only the listed networks. The
parentheses may be omitted if only a single net 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.
nets=dynamic
Defines the zone as dynamic. Requires ipset match support in your iptables and
kernel. See https://shorewall.org/Dynamic.html[12] for further information.
nodbl
Added in Shorewall 5.0.8. When specified, dynamic blacklisting is disabled on the
interface. Beginning with Shorewall 5.0.10, nodbl is equivalent to dbl=none.
nosmurfs
IPv4 only. Filter packets for smurfs (packets with a broadcast address as the
source).
Smurfs will be optionally logged based on the setting of SMURF_LOG_LEVEL in
shorewall.conf[7](5). After logging, the packets are dropped.
omitanycast
IPv6 only. Added in Shorewall 5.2.8.
Shorewall6 has traditionally generated rules for IPv6 anycast addresses. These
rules include:
1. Packets with these destination IP addresses are dropped by REJECT rules.
2. Packets with these source IP addresses are dropped by the 'nosmurfs' interface
option and by the 'dropSmurfs' action.
3. Packets with these destination IP addresses are not logged during policy
enforcement.
4. Packets with these destination IP addresses are processes by the 'Broadcast'
action.
This can be inhibited for individual interfaces by specifying noanycast for those
interfaces.
Note
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.
optional
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 enable and
disable commands on the interface.
When optional is specified for an interface, Shorewall will be silent when:
• a /proc/sys/net/ipv[46]/conf/ entry for the interface cannot be modified
(including for proxy ARP or proxy NDP).
• The first address of the interface cannot be obtained.
• The gateway of the interface can not be obtained (provider interface).
• The interface has been disabled using the disable command.
May not be specified with required.
physical=name
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 https://shorewall.org/bridge-Shorewall-perl.html#Multiple[13].
If the interface name is a wildcard name (ends with '+'), then the physical name
must also end in '+'. The physical name may end in '+' (or be exactly '+') when
the interface name is not a wildcard name.
If physical is not specified, then it's value defaults to the interface name.
proxyarp[={0|1}]
IPv4 only. Sets /proc/sys/net/ipv4/conf/interface/proxy_arp. Do NOT use this
option if you are employing Proxy ARP through entries in
shorewall-proxyarp[14](5). This option is intended solely for use with Proxy ARP
sub-networking as described at:
http://tldp.org/HOWTO/Proxy-ARP-Subnet/index.html.[15]
Note
This option does not work with a wild-card physical name (e.g., eth0.+).
Beginning with Shorewall 5.1.10, If this option is specified, a warning is
issued and the option is ignored.
Only those interfaces with the proxyarp 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.
proxyndp[={0|1}]
IPv6 only. Sets /proc/sys/net/ipv6/conf/interface/proxy_ndp.
Note
This option does not work with a wild-card physical name (e.g., eth0.+).
Beginning with Shorewall 5.1.10, If this option is specified, a warning is
issued and the option is ignored.
Only those interfaces with the proxyndp 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.
required
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 optional.
routeback[={0|1}]
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.
Beginning with Shorewall 4.4.20, if you specify this option, then you should also
specify either sfilter (see below) or routefilter on all interfaces (see below).
Beginning with Shorewall 4.5.18, you may specify this option to explicitly reset
(e.g., routeback=0). This can be used to override Shorewall's default setting for
bridge devices which is routeback=1.
routefilter[={0|1|2}]
IPv4 only. Turn on kernel route filtering for this interface (anti-spoofing
measure).
Only those interfaces with the routefilter 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.
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 loose form of reverse path filtering.
Note
This option does not work with a wild-card physical name (e.g., eth0.+).
Beginning with Shorewall 5.1.10, If this option is specified, a warning is
issued and the option is ignored.
This option can also be enabled globally via the ROUTE_FILTER option in the
shorewall.conf[7](5) file.
Important
If ROUTE_FILTER=Yes in shorewall.conf[7](5), or if your distribution sets
net.ipv4.conf.all.rp_filter=1 in /etc/sysctl.conf, then setting routefilter=0
in an interface entry will not disable route filtering on that interface! The
effective setting for an interface is the maximum of the contents of
/proc/sys/net/ipv4/conf/all/rp_filter and the routefilter setting specified in
this file (/proc/sys/net/ipv4/conf/interface/rp_filter).
Note
There are certain cases where routefilter cannot be used on an interface:
• If USE_DEFAULT_RT=Yes in shorewall.conf[7](5) and the interface is listed
in shorewall-providers[16](5).
• If there is an entry for the interface in shorewall-providers[16](5) that
doesn't specify the balance option.
• 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
routefilter.
Beginning with Shorewall 5.1.1, when routefilter is set to a non-zero value, the
logmartians option is also implicitly set. If you actually want route filtering
without logging, then you must also specify logmartians=0 after routefilter.
rpfilter
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 sfilter option below. It performs a function similar
to routefilter (see above) but works with Multi-ISP configurations that do not use
balanced routes.
sfilter=(net[,...])
Added in Shorewall 4.4.20. This option provides an anti-spoofing alternative to
routefilter on interfaces where that option cannot be used, but where the
routeback option is required (on a bridge, for example). On these interfaces,
sfilter should list those local networks that are connected to the firewall
through other interfaces.
sourceroute[={0|1}]
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.
Only those interfaces with the sourceroute 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.
Note
This option does not work with a wild-card physical name (e.g., eth0.+).
Beginning with Shorewall 5.1.10, If this option is specified, a warning is
issued and the option is ignored.
tcpflags[={0|1}]
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.
Beginning with Shorewall 4.6.0, tcpflags=1 is the default. To disable this option,
specify tcpflags=0.
unmanaged
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:
• The ZONE column must contain '-'.
• Only the following other options are allowed with unmanaged:
arp_filter
arp_ignore
ignore
routefilter
optional
physical
routefilter
proxyarp
proxyudp
sourceroute
upnp
Incoming requests from this interface may be remapped via UPNP (upnpd). See
https://shorewall.org/UPnP.html[17]. Supported in IPv4 and in IPv6 in Shorewall
5.1.4 and later.
upnpclient
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.
wait=seconds
Added in Shorewall 4.4.10. Causes the generated script to wait up to seconds
seconds for the interface to become usable before applying the required or
optional options.
EXAMPLE
IPv4 Example 1:
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.
Your entries for this setup would look like:
?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
Example 2:
The same configuration without specifying broadcast addresses is:
?FORMAT 2
#ZONE INTERFACE OPTIONS
net eth0 dhcp
loc eth1
dmz eth2
Example 3:
You have a simple dial-in system with no Ethernet connections.
?FORMAT 2
#ZONE INTERFACE OPTIONS
net ppp0 -
Example 4 (Shorewall 4.4.9 and later):
You have a bridge with no IP address and you want to allow traffic through the bridge.
?FORMAT 2
#ZONE INTERFACE OPTIONS
- br0 bridge
FILES
/etc/shorewall/interfaces
/etc/shorewall6/interfaces
SEE ALSO
https://shorewall.org/configuration_file_basics.htm#Pairs[18]
shorewall(8)
NOTES
1. shorewall-hosts
https://shorewall.org/manpages/shorewall-hosts.html
2. https://shorewall.org/FAQ.htm#faq18
https://shorewall.org/FAQ.htm#faq18
3. shorewall-nesting
https://shorewall.org/manpages/shorewall-nesting.html
4. shorewall6-zones
https://shorewall.org/manpages/shorewall-zones.html
5. Proxy ARP
https://shorewall.org/ProxyARP.htm
6. shorewall-blacklist
https://shorewall.org/manpages/shorewall-blacklist.html
7. shorewall.conf(5)
https://shorewall.org/manpages/shorewall.conf.html
8. simple bridge
https://shorewall.org/SimpleBridge.html
9. Shorewall-perl for firewall/bridging
https://shorewall.org/bridge-Shorewall-perl.html
10. shorewall-rules
https://shorewall.org/manpages/shorewall-rules.html
11. shorewall-maclist
https://shorewall.org/manpages/shorewall-maclist.html
12. https://shorewall.org/Dynamic.html
https://shorewall.org/Dynamic.html
13. https://shorewall.org/bridge-Shorewall-perl.html#Multiple
https://shorewall.org/bridge-Shorewall-perl.html#Multiple
14. shorewall-proxyarp
https://shorewall.org/manpages/shorewall-proxyarp.html
15. http://tldp.org/HOWTO/Proxy-ARP-Subnet/index.html.
http://tldp.org/HOWTO/Proxy-ARP-Subnet/index.html
16. shorewall-providers
https://shorewall.org/manpages/shorewall-providers.html
17. https://shorewall.org/UPnP.html
https://shorewall.org/UPnP.html
18. https://shorewall.org/configuration_file_basics.htm#Pairs
https://shorewall.org/configuration_file_basics.htm#Pairs