Provided by: shorewall_5.2.8-2_all 
NAME
names - Shorewall object names
DESCRIPTION
When you define an object in Shorewall (Zone[1], Logical Interface, ipsets[2], Actions[3],
etc., you give it a name. Shorewall names start with a letter and consist of letters,
digits or underscores ("_"). Except for Zone names, Shorewall does not impose a limit on
name length.
When an ipset is referenced, the name must be preceded by a plus sign ("+").
The last character of an interface may also be a plus sign to indicate a wildcard name.
Physical interface names match names shown by 'ip link ls'; if the name includes an at
sign ("@"), do not include that character or any character that follows. For example,
"sit1@NONE" is referred to as simply 'sit1".
ZONE AND CHAIN NAMES
For a pair of zones, Shorewall creates two Netfilter chains; one for connections in each
direction. The names of these chains are formed by separating the names of the two zones
by either "2" or "-".
Example: Traffic from zone A to zone B would go through chain A2B (think "A to B") or
"A-B".
In Shorewall 4.6, the default separator is "-" but you can override that by setting
ZONE_SEPARATOR="2" in shorewall.conf[4] (5).
Note
Prior to Shorewall 4.6, the default separator was "2".
Zones themselves have names that begin with a letter and are composed of letters,
numerals, and "_". The maximum length of a name is dependent on the setting of LOGFORMAT
in shorewall.conf[4] (5). See shorewall-zones[1] (5) for details.
USING DNS NAMES
Caution
I personally recommend strongly against using DNS names in Shorewall configuration
files. If you use DNS names and you are called out of bed at 2:00AM because Shorewall
won't start as a result of DNS problems then don't say that you were not forewarned.
Host addresses in Shorewall configuration files may be specified as either IP addresses or
DNS Names.
DNS names in iptables rules aren't nearly as useful as they first appear. When a DNS name
appears in a rule, the iptables utility resolves the name to one or more IP addresses and
inserts those addresses into the rule. So changes in the DNS->IP address relationship that
occur after the firewall has started have absolutely no effect on the firewall's rule set.
For some sites, using DNS names is very risky. Here's an example:
teastep@ursa:~$ dig pop.gmail.com
; <<>> DiG 9.4.2-P1 <<>> pop.gmail.com
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 1774
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 7, ADDITIONAL: 0
;; QUESTION SECTION:
;pop.gmail.com. IN A
;; ANSWER SECTION:
pop.gmail.com. 300 IN CNAME gmail-pop.l.google.com.
gmail-pop.l.google.com. 300 IN A 209.85.201.109
gmail-pop.l.google.com. 300 IN A 209.85.201.111
Note that the TTL is 300 -- 300 seconds is only 5 minutes. So five minutes later, the
answer may change!
So this rule may work for five minutes then suddently stop working:
#ACTION SOURCE DEST PROTO DPORT
POP(ACCEPT) loc net:pop.gmail.com
There are two options in shorewall[6].conf(5)[4] that affect the use of DNS names in
Shorewall[6] config files:
• DEFER_DNS_RESOLUTION - When set to No, DNS names are resolved at compile time; when
set to Yes, DNS Names are resolved at runtime.
• AUTOMAKE - When set to Yes, start, restart and reload only result in compilation if
one of the files on the CONFIG_PATH has changed since the the last compilation.
So by setting AUTOMAKE=Yes, and DEFER_DNS_RESOLUTION=No, compilation will only take place
at boot time if a change had been make to the config but no restart or reload had taken
place. This is clearly spelled out in the shorewall.conf manpage. So with these settings,
so long as a 'reload' or 'restart' takes place after the Shorewall configuration is
changes, there should be no DNS-related problems at boot time.
Important
When DEFER_DNS_RESOLUTION=No and AUTOMAKE=Yes and a DNS change makes it necessary to
recompile an existing firewall script, the -c option must be used with the reload or
restart command to force recompilation.
If your firewall rules include DNS names then, even if DEFER_DNS_RESOLUTION=No and
AUTOMAKE=Yes:
• If your /etc/resolv.confis wrong then your firewall may not start.
• If your /etc/nsswitch.conf is wrong then your firewall may not start.
• If your Name Server(s) is(are) down then your firewall may not start.
• If your startup scripts try to start your firewall before starting your DNS server
then your firewall may not start.
• Factors totally outside your control (your ISP's router is down for example), can
prevent your firewall from starting.
• You must bring up your network interfaces prior to starting your firewall, or the
firewall may not start.
Each DNS name must be fully qualified and include a minimum of two periods (although one
may be trailing). This restriction is imposed by Shorewall to insure backward
compatibility with existing configuration files.
Example 1. Valid DNS Names
• mail.shorewall.net
• shorewall.net. (note the trailing period).
Example 2. Invalid DNS Names
• mail (not fully qualified)
• shorewall.net (only one period)
DNS names may not be used as:
• The server address in a DNAT rule (/etc/shorewall/rules file)
• In the ADDRESS column of an entry in /etc/shorewall/masq.
•
• In the /etc/shorewall/nat file.
These restrictions are imposed by Netfilter and not by Shorewall.
LOGICAL INTERFACE NAMES
When dealing with a complex configuration, it is often awkward to use physical interface
names in the Shorewall configuration.
• You need to remember which interface is which.
• If you move the configuration to another firewall, the interface names might not be
the same.
Beginning with Shorewall 4.4.4, you can use logical interface names which are mapped to
the actual interface using the physical option in shorewall-interfaces[5] (5).
Here is an example:
#ZONE INTERFACE OPTIONS
net COM_IF dhcp,blacklist,tcpflags,optional,upnp,routefilter=0,nosmurfs,logmartians=0,physical=eth0
net EXT_IF dhcp,blacklist,tcpflags,optional,routefilter=0,nosmurfs,logmartians=0,proxyarp=1,physical=eth2
loc INT_IF dhcp,logmartians=1,routefilter=1,tcpflags,nets=172.20.1.0/24,physical=eth1
dmz VPS_IF logmartians=1,routefilter=0,routeback,physical=venet0
loc TUN_IF physical=tun+
In this example, COM_IF is a logical interface name that refers to Ethernet interface
eth0, EXT_IF is a logical interface name that refers to Ethernet interface eth2, and so
on.
Here are a couple of more files from the same configuration:
shorewall-masq[6] (5):
#INTERFACE SOURCE ADDRESS
COMMENT Masquerade Local Network
COM_IF 0.0.0.0/0
EXT_IF !206.124.146.0/24 206.124.146.179:persistent
shorewall-providers[7] (5)
#NAME NUMBER MARK DUPLICATE INTERFACE GATEWAY OPTIONS COPY
Avvanta 1 0x10000 main EXT_IF 206.124.146.254 loose,fallback INT_IF,VPS_IF,TUN_IF
Comcast 2 0x20000 main COM_IF detect balance INT_IF,VPS_IF,TUN_IF
Note in particular that Shorewall translates TUN_IF to tun* in the COPY column.
NOTES
1. Zone
https://shorewall.org/manpages/shorewall-zones.html
2. ipsets
https://shorewall.org/manpages/ipsets.html
3. Actions
https://shorewall.org/manpages/Actions.html
4. shorewall.conf
https://shorewall.org/manpages/shorewall.conf.html
5. shorewall-interfaces
https://shorewall.org/manpages/shorewall-interfaces.html
6. shorewall-masq
https://shorewall.org/manpages/shorewall-masq.html
7. shorewall-providers
https://shorewall.org/manpages/shorewall-providers.html