Aliases

Aliases define a group ports, hosts, or networks. Aliases can be referenced by firewall rules, port forwards, outbound NAT rules, and other places in the firewall. Using aliases results in rulesets that are significantly shorter, self-documenting, and more manageable.

Note

Firewall aliases are collections of entries for use by the firewall. Despite the similar names, this is different than interface IP aliases, which are a means of adding additional IP addresses to a network interface (Virtual IP Addresses).

Aliases are located at Firewall > Aliases. The page is divided into separate tabs for each type of alias: IP, Ports, URLs, and the All tab which shows every alias in one large list. When creating an alias, add it to any tab and it will be sorted to the correct location based on the type chosen.

Nesting Aliases

Most aliases can be nested inside of other aliases to collect many entries into larger groups. For example, one alias can nest an alias containing web servers, an alias containing mail servers, and a servers alias that contains both the web and mail server aliases all together in one larger Servers alias.

To nest, aliases must be either the same or compatible types. For example, a network type alias cannot nest a port alias since they are not the same type of alias. However, host and network aliases can nest each other since they are compatible. URL table aliases can nest other URL table aliases, and URL aliases can nest other URL aliases.

Using Hostnames in Aliases

Host and network type aliases support entries consisting of fully qualified domain name (FQDN) style hostnames (e.g. host.domain.com) in regular or IDN format. The firewall must be able to resolve the hostname as-is using A or AAAA type DNS queries in order for these entries to function. This means that the firewall must have working DNS, and the FQDN must exist in the DNS servers used by the firewall.

Warning

This process only supports forward name resolution of FQDNs using A and AAAA records such as host.domain.com. Aliases do not support pattern matches, wildcard matches (e.g. *.domain.com), or any other style of record comparison.

If the DNS query for a hostname returns multiple IP addresses, all of the IP addresses returned in the result at the time the query is made are added to the alias.

Note

This feature is not useful for allowing or disallowing users to large public web sites such as those served by content delivery network (CDN) providers. Such sites tend to have constantly rotating or random responses to DNS queries so the contents of the alias on the firewall do not necessarily match up with the response a user will receive when they resolve the same site name. It can work for smaller sites that have only a few servers and do not include incomplete sets of addresses in their DNS responses.

A hostname entry in a host or network type alias is periodically resolved and updated by the firewall every few minutes. The default interval is 300 seconds (5 minutes), and can be changed by adjusting the value of Aliases Hostnames Resolve Interval on System > Advanced, Firewall & NAT tab. This is useful for tracking dynamic DNS entries to allow specific users into services from dynamic IP addresses.

Mixing IPv4 and IPv6 Addresses in Aliases

IPv4 and IPv6 addresses can be mixed inside an alias. The firewall will use the appropriate type of addresses when the alias is referenced in a specific rule.

Alias Sizing Concerns

The total size of all tables must fit in roughly half the amount of Firewall Maximum Table Entries, which defaults to 400000. If the maximum number of table entries is not large enough to contain all of the entries, the rules may fail to load. See Firewall Maximum Table Entries for information on changing that value. The aliases must fit in twice in the total area because of the way aliases are loaded and reloaded; The new list is loaded alongside the old list and then the old one is removed.

This value can be increased as much required provided that the firewall contains sufficient RAM to hold the entries. The RAM usage is similar to, but less than, the state table but it is still safe to assume approximately 1K of memory per entry to be conservative.

Alias Settings

When editing an Alias entry, the following settings are available:

Name:

A Name for the alias. The name may only consist of the characters a-z, A-Z, 0-9 and _.

Description:

A Description for the alias.

Type:

The Type for the alias, which alters the behavior of the alias and tells the firewall which types of entries can be added to the alias.

The following types are available:

Host:

Aliases containing single IP addresses or FQDN hostnames

Network:

Aliases containing CIDR-masked lists of networks, FQDN hostnames, IP address ranges, or single IP addresses

Port:

These aliases contain lists of port numbers or ranges of ports for TCP or UDP.

URL (IP or Port):

The alias is built from the content returned by the specified URL, but is read only a single time. Once added, it becomes a normal network or port type alias.

URL Table (IP or Port):

The alias is built from the content returned by the specified URL but is updated by fetching the list from the URL periodically.

Entries:

The lower section of the alias page contains the entries for the alias. The behavior of this section varies based on the selected alias type.

The next sections describe the behavior of each type in more detail.

Host Aliases

Host type aliases contain groups of IP addresses. For Host type aliases, entries are specified by IP address or fully qualified domain name (FQDN).

If an IP address range such as 192.168.1.1-192.168.1.10 or a small subnet such as 192.168.1.16/28 is entered in this field, the firewall will translate it into a list of individual IP addresses when saving the alias.

Figure Example Hosts Alias shows an example of a host type alias used to contain a list of public web servers.

Example Hosts Alias

Other host type aliases can be nested inside this entry. Hostnames may also be used as entries, as explained previously.

Network Aliases

For Network type aliases, entries are specified in CIDR format for subnets or fully qualified domain names (FQDN) for single addresses.

For subnets, select the CIDR mask that pertains to each entry. /32 specifies a single IPv4 host, /128 specifies a single IPv6 host, /24 specifies 255.255.255.0, /64 specifies a normal IPv6 network, etc.

Hostnames (FQDNs) may also be specified, using a /32 mask for IPv4 or /128 for IPv6.

Figure Example Network Alias shows an example of a network alias that is used later in this chapter.

Example Network Alias

Other host or network aliases can be nested inside this entry. Hostnames may also be used as entries, as explained previously.

When an alias entry contains an IPv4 range it is automatically translated by the firewall to an equivalent set of IPv4 CIDR networks that will exactly contain the provided range. As shown in Figure Example IP Range After, the range is expanded when the alias is saved, and the resulting list of IPv4 CIDR networks will match exactly the requested range.

Example IP Range Before

Example IP Range After

Port Aliases

Port type aliases contain groups of ports and port ranges. A single port is an integer from 1-65535. A port range is two ports separated by a colon (:), for example, 1194:1199 and matches the specified ports and any ports in between.

The protocol is not specified in the alias; The firewall rule where the alias is used will define the protocol as TCP, UDP, or both. Figure Example Ports Alias shows an example of a port type alias.

Example Ports Alias

Enter another port-type alias name into the Port field to nest other port-type aliases inside this alias.

URL Aliases

With a URL type alias, each entry contains a URL which returns text content containing a list of entries. Multiple URLs may be entered.

When Save is clicked, up to 3,000 entries from each URL are read from the file and imported into a network type alias.

If URL (IPs) is selected, then the URLs must contain IP address, CIDR masked network entries, or FQDNs, and the firewall creates a network type alias from the contents.

If URL (Ports) is selected, then the URL must contain only port numbers or ranges, and the firewall creates a port type alias from the contents.

For a URL type alias, the contents of the alias are re-fetched every 24 hours from the stored URL by the firewall.

URL Table Aliases

A URL Table alias behaves in a significantly different way than the URL alias. For starters, it does not import the contents of the file into a normal alias. It downloads the contents of the URL into a special location on the firewall and uses the contents for what is called a persist table, also known as a file-based alias. The full contents of the alias are not directly editable in the GUI, but can be viewed in the Tables viewer (See Firewall Table Contents).

For a URL Table alias, the drop-down list after the / controls how many days must pass before the contents of the alias are re-fetched from the stored URL by the firewall. When the time comes, the alias contents will be updated overnight by a script which re-fetches the data.

URL Table aliases can be quite large, containing many thousands of entries. Some customers use them to hold lists of all IP blocks in a given country or region, which can easily surpass 40,000 entries. The pfBlockerNG package uses this type of alias when handling country lists and other similar actions.

If URL Table (IPs) is selected, then the URLs must contain IP address, CIDR masked network entries, or FQDNs, and the firewall creates a network type alias from the contents.

If URL Table (Ports) is selected, then the URL must contain only port numbers or ranges, and the firewall creates a port type alias from the contents.

Configuring Aliases

To add an alias:

• Navigate to Firewall > Aliases

• Click Add

• Enter settings as described in Alias Settings

• Enter the type-specific information as needed. Each type has an data field and a description field for each entry.

To add new members to an alias, click Add at the bottom of the list of entries.

To remove members from an alias, click Delete at the end of the row to remove.

When the alias is complete, click Save to store the alias contents.

Each manually entered alias is limited to 5,000 members, but some browsers have trouble displaying or using the page with more than around 3,000 entries. For large numbers of entries, use a URL Table type alias which is capable of handling larger lists.

Bulk Import Network Aliases

Another method of importing multiple entries into an alias is to use the bulk import feature.

To use the import feature:

• Navigate to Firewall > Aliases

• Click Import

• Fill in the Alias Name and Description

• Enter the alias contents into the Aliases to import text area, one entry per line.

• Click Save

Common usage examples for this page include lists of IP addresses, networks, and blacklists. The list may contain IP addresses, CIDR masked networks, IP ranges, or port numbers. The firewall will attempt to determine the target alias type automatically.

The firewall imports items into a normal alias which can be edited later.

Using Aliases

When a letter is typed into an input box which supports aliases, the GUI displays a list of matching aliases. Select the desired alias from the list, or type its name out completely.

Note

Alias autocompletion is not case sensitive but it is restricted by type. For example, a Network or Host type alias will be listed in autocomplete for a Network field, but a Port alias will not; A port alias can be used in a port field, but a Network alias will not be in the list.

Figure Autocompletion of Hosts Alias shows how the WebServers alias, configured as shown in Figure Example Hosts Alias, can be used in the Destination field when adding or editing a firewall rule.

• Edit the firewall rule

• Select Address or Alias

• Then type the first letter of the desired alias: Enter W and the alias appears as shown.

Autocompletion of Hosts Alias

Figure Autocompletion of Ports Alias shows the autocompletion of the ports alias configured as shown in Figure Example Ports Alias. If multiple aliases match the letter entered, all matching aliases of the appropriate type are listed. Click on the desired alias to select it.

Autocompletion of Ports Alias

Figure Example Rule Using Aliases shows the rule created using the WebServers and WebPorts aliases. This rule is on WAN, and allows any source to the IP addresses defined in the WebServers alias when using the ports defined in the WebPorts alias.

Example Rule Using Aliases

Hovering the mouse cursor over an alias on the Firewall > Rules page shows a tooltip displaying the contents of the alias with the descriptions included in the alias. Figure Hovering Shows Hosts Contents shows this for the WebServers alias and Figure Hovering Shows Ports Contents for the ports alias.

Hovering Shows Hosts Contents

Hovering Shows Ports Contents