interfaces — Shorewall interfaces file
/etc/shorewall[6]/interfaces
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:
There is a BROADCAST column which can be used to specify the broadcast address associated with the interface.
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 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(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 -
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.
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(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(5).
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.
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.
IPv6 only; added in Shorewall 4.5.16. Values are:
Do not accept Router Advertisements.
Accept Route Advertisements if forwarding is disabled.
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.
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.
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.
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.
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
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.
Do not specify arp_ignore for any interface involved in Proxy ARP.
Checks packets arriving on this interface against the shorewall-blacklist(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(5).
Otherwise, the option is ignored with a warning:
WARNING: The 'blacklist' option is ignored on multi-zone interfaces
Designates the interface as a bridge. Beginning with
Shorewall 4.4.7, setting this option also sets
routeback.
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.
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)). The default is determine by the setting of DYNAMIC_BLACKLIST:
Default is none (e.g., no dynamic blacklist checking).
Default is src (e.g., the source IP address is checked).
Default is src.
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.
Added in Shorewall 4.5.17. Causes the compiler to omit rules to handle traffic from this interface.
Specify this option when any of the following are true:
the interface gets its IP address via DHCP
the interface is used by a DHCP server running on the firewall
the interface has a static IP but is on a LAN segment with lots of DHCP clients.
the interface is a simple bridge with a DHCP server on one port and DHCP clients on another port.
If you use Shorewall-perl for firewall/bridging, then you need to include DHCP-specific rules in shorewall-rules(5). DHCP uses UDP ports 67 and 68.
This option allows DHCP datagrams to enter and leave the interface.
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.
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.
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.
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.
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/
- a non-zero value indicates that route filtering is
enabled.interface/rp_filter
Example:
teastep@lists:~$ cat /proc/sys/net/ipv4/conf/eth0/rp_filter
1
teastep@lists:~$ 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(5) file.
Connection requests from this interface are compared against the contents of shorewall-maclist(5). If this option is specified, the interface must be an Ethernet NIC and must be up before Shorewall is started.
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.
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.
Defines the zone as dynamic. Requires ipset match support in your iptables and kernel. See https://shorewall.org/Dynamic.html for further information.
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.
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(5). After logging, the packets are dropped.
IPv6 only. Added in Shorewall 5.2.8.
Shorewall6 has traditionally generated rules for IPv6 anycast addresses. These rules include:
Packets with these destination IP addresses are dropped by REJECT rules.
Packets with these source IP addresses are dropped by the 'nosmurfs' interface option and by the 'dropSmurfs' action.
Packets with these destination IP addresses are not logged during policy enforcement.
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.
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.
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.
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.
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.
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(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.
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.
IPv6 only. Sets /proc/sys/net/ipv6/conf/interface/proxy_ndp.
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.
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.
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.
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.
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(5) file.
If ROUTE_FILTER=Yes in shorewall.conf(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).
There are certain cases where
routefilter cannot be used on an
interface:
If USE_DEFAULT_RT=Yes in shorewall.conf(5) and the interface is listed in shorewall-providers(5).
If there is an entry for the interface in shorewall-providers(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.
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.
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.
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.
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.
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.
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 |
Incoming requests from this interface may be remapped via UPNP (upnpd). See https://shorewall.org/UPnP.html. Supported in IPv4 and in IPv6 in Shorewall 5.1.4 and later.
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.
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.
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
The same configuration without specifying broadcast addresses is:
?FORMAT 2 #ZONE INTERFACE OPTIONS net eth0 dhcp loc eth1 dmz eth2
You have a simple dial-in system with no Ethernet connections.
?FORMAT 2 #ZONE INTERFACE OPTIONS net ppp0 -
You have a bridge with no IP address and you want to allow traffic through the bridge.
?FORMAT 2 #ZONE INTERFACE OPTIONS - br0 bridge