# Aliases¶

Aliases are named lists of networks, hosts or ports that can be used as one entity by selecting the alias name in the various supported sections of the firewall. These aliases are particularly useful to condense firewall rules and minimize changes.

Aliases can be added, modified and removed via Firewall ‣ Aliases.

## Overview¶

The page opens with an overview of the aliases available, including some internal ones available from installed software. At the top of the page you can search for aliases or preselect various types or categories to which they belong.

In order to gain some insights into the current status of the plugins, two additional (meta) fields are being displayed, being:

• Shows the amount of entries planned to install into the table, in case there’s not enough memory available to load the item in question, one can easily find the alias causing the overflow in table entries (bar at the right top of the page)

• Last updated

• Shows the last timestamp from the entries saved to disk.

## Alias Types¶

OPNsense offers the following alias types:

Type

Description

Hosts

Single hosts by IP or Fully Qualified Domain Name or host exclusions (starts with “!” sign)

Networks

Entire network p.e. 192.168.1.1/24 or network exclusion eg !192.168.1.0/24

Ports

Port numbers or a port range like 20:30

MAC address or partial mac addresses like f4:90:ea

URL (IPs)

A table of IP addresses that are fetched once

URL Tables (IPs)

A table of IP addresses that are fetched on regular intervals.

GeoIP

Select countries or whole regions

Network group

Combine different network type aliases into one

Dynamic IPv6 Host

A Host entry that will auto update on a prefixchange

BGP ASN

Maps autonomous system (AS) numbers to networks where they are responsible for.

Internal (automatic)

Internal aliases which are managed by the product

Externally managed alias, this only handles the placeholder. Content is set from another source (plugin, api call, etc)

### Hosts¶

Hosts can be entered as a single IP address, a range (separated with a minus sign, e.g. 10.0.0.1-10.0.0.10) or a fully qualified domain name.

When using a fully qualified domain name, the name will be resolved periodically (default is each 300 seconds).

Sample

Let’s say we want to create an alias table for www.youtube.com

Apply changes and look at the content of our newly created pf table.

Go to Firewall ‣ Diagnostics ‣ Aliases and select our newly created youtube table.

As you can see there are multiple IP addresses for this domain.

Tip

To change the alias domain resolve interval, go to Firewall ‣ Settings ‣ Advanced and set Aliases Resolve Interval to the number of seconds to refresh.

Hosts type Aliases can contain exclusion hosts. Exclusion addresses starts with “!” sign (eg !192.168.0.1) and can be used to exclude hosts from Network Group Aliases.

Warning

Please note thet the Flush action is not persistent!

“flush” means flush the current contents of the alias, which will be repopulated when it’s not an external type, so flush in most cases isn’t very useful.

Same behaviour applies to the API call alias_util flush

### Networks¶

Networks are specified in Classless Inter-Domain Routing format (CIDR). Use the the correct CIDR mask for each entry. For instance a /32 specifies a single IPv4 host, or /128 specifies a single IPv6 host, whereas /24 specifies 255.255.255.0 and /64 specifies a normal IPv6 network. Network type Aliases can contain exclusion hosts or networks. Exclusion addresses starts with “!” sign (eg !192.168.0.0/24) and can be used to exclude hosts or networks from current Alias or Network Group Alias

Apart from the CIDR notation, one could also use a wildcard mask to match ranges of hosts or networks.

Tip

To match all servers ending at .1 in the 192.168.X.1 networks, use a wildcard definition like 192.168.0.1/0.0.255.0

### Ports¶

Ports can be specified as a single number or a range using a colon :. For instance to add a range of 20 to 25 one would enter 20:25 in the Port(s) section.

Hardware mac addresses can be specified as a (partial) hex value, such as F4:90:EA to match all addresses from Deciso or f4:90:ea:00:00:01 to match a single item (the input is case insensitive).

The way these aliases function is approximately the same as hostnames in host type aliases, they are resolved on periodic intervals from the arp and ndp tables.

Warning

Please be aware that hardware addresses can be spoofed (https://en.wikipedia.org/wiki/MAC_spoofing), which doesn’t make filters on them more secure than ip addresses in any way.

Note

Since mappings between addresses and mac addresses are resolved periodically the actual situation can differ, you can always check Firewall -> Diagnostics -> Aliases to inspect the current contents of the alias.

### URL Tables¶

URL tables can be used to fetch a list of IP addresses from a remote server. There are several IP lists available for free, most notably are the “Don’t Route Or Peer” lists from Spamhaus.

Note

The content of the file being fetched should contain one IPv[4|6] address per line, lines that start with a whitespace , colon (,), semicolon (;), pipe (|) or hash (#) will be ignored.

### GeoIP¶

With GeoIP alias you can select one or more countries or whole continents to block or allow. Use the toggle all checkbox to select all countries within the given region.

To use GeoIP, you need to configure a source in the Firewall ‣ Aliases -> GeoIP settings tab, the most commonly used source is MaxMind, for which we have a how-to available : MaxMind GeoIP’s Setup

The configured url should point to a zip file containing the following csv files:

Title

Filename

Purpose

Format

Example

%prefix%-locations-en.csv

maps geo locations to iso countries

geoname_id,,,,country_iso_code

1,,,,NL

%prefix%-IPv4.csv

IPv4 networks

network,geoname_id

2.21.241.0/28,1

%prefix%-IPv6.csv

IPv6 networks

network,geoname_id

2001:470:1f15:210::/64,1

The %prefix% can be used to identify the product and/or vendor, in MaxMind’s case these files are named GeoLite2-Country-Locations-en.csv, GeoLite2-Country-Blocks-IPv4.csv, GeoLite2-Country-Blocks-IPv6.csv for example.

Tip

Geo ip lists can be rather large, especially when using IPv6. When creating rules, always try to minimize the number of addresses needed in your selection. A selection of all countries in the world not being the Netherlands can usually be rewritten as only addresses from the Netherlands for example.

Tip

If the number of items is larger than the allocated alias size, you can assign more memory to aliases. Firewall ‣ Settings ‣ Advanced : Firewall Maximum Table Entries

### Network group¶

Combine different network type aliases into one, this type of alias accepts other host type aliases (networks, hosts, …). Although nesting is possible with other alias types as well, this type only displays valid aliases easing administration, functionally a Networks type alias can do the same but uses a different presentation.

### Dynamic IPv6 Host¶

An IPv6 Dynamic Host is used where the system is using a dynamic prefix on the LAN, a tracking interface. When the prefix changes, either due to the ISP changing the prefix at will or the prefix changes when the WAN connection is reset, any alias containing an address of a client such as a server on the LAN would no longer be valid.

For example, you obtain a prefix 2001:db8:2222:2800::/56. You have a /56 prefix and if the tracking id was set to 0 for your LAN, you would have an address range on your LAN of 2001:db8:2222:2800:: to 2001:db8:2222:2800:FFFF:FFFF:FFFF:FFFF.

You want to run a server on your LAN that is accessable from the WAN so you give it a static address of 2001:db8:2222:2800:1000:1000::1 and create a rule allowing traffic to access the server.

When your prefix changes, that static address is no longer valid, so you must use the Dynamic IPv6 Host to create an alias address for the firewall entry that automatically tracks the prefix and changes the rule.

The Dynamic Host Alias will always split on the /64 boundary, it will take the upper 64 bits from the interface you select and the lower 64 bits from the address you enter. It does not matter what size your prefix delegation is.

Create a new IPv6 Dynamic Host alias and enter only the suffix of the address, in this example, we will enter the lower 64 bits of the address, you would enter ::1000:1000:0000:1, note the ‘::’ at the start of the address, you MUST always start the address with a ‘::’. You do not need to enter a size after the address i.e. /128 as that is automatically assumed.

Select the interface you wish to use for the source of the uppper 64 bits, in this case we will select the LAN interface.

When the prefix changes, the alias address will then be updated in the firewall rules, let’s say your prefix changes to 2001:db8:2222:3200::/56 the rule updates and the entry for your server in the firewall would update automatically to be 2001:db8:2222:3200:1000:1000::1

Let’s take another example, you have a /48 prefix delegation, you have two LAN interfaces and a server on each. You would need to create two separate Dynamic IPv6 Host entries, one for each LAN. For simplicities sake we will use the same address for each server on each interface, you would enter ::aaaa:bbbb:cccc:0001 as the address.

Upper 64 bits, taken from LAN 1 Interface

Server 1: 2a02:1234:5678:0000

aaaa:bbbb:cccc:0001

Server 1 GUA address is: 2a02:1234:5678:0000:aaaa:bbbb:cccc:0001

Upper 64 bits, taken from LAN 2 Interface

Server 2: 2a02:1234:5678:0001

aaaa:bbbb:cccc:0001

Server 2 GUA address is: 2a02:1234:5678:0001:aaaa:bbbb:cccc:0001

The prefix changes, in this case we have a /48 prefix, so the new prefix is 2a02:1234:5679/48 our aliases would update to give us the following addresses:

 LAN 1: Server 1 GUA address is: 2a02:1234:5679:0000:aaaa:bbbb:cccc:0001 LAN 2: Server 2 GUA address is: 2a02:1234:5679:0001:aaaa:bbbb:cccc:0001

You may enter multiple addresses, for example if you have several servers on the same LAN segment, just add the suffix for each one. In the example below we have three servers.

### BGP ASN¶

With this alias type you are able to select networks by their responsible parties. Using BGP parties announce the addresses they are responsible for to eachother. For example Cloudflare uses AS number 13335, Microsoft is known to use 8075.

More background and how addresses are assigned is explained on wikipedia

### External¶

The contents for external alias types is not administered via our normal alias service and can be practical in scenarios where you want to push new entries from external programs. Such as specific lockout features or external tools feeding access control to your firewall.

In Firewall ‣ Diagnostics ‣ Aliases you can always inspect the current contents of the external alias and add or remove entries immediately.

Tip

When changing alias contents which are used on firewall rules with state tracking enabled, you might need to remove the specific state before the new rule turns active. (see Firewall ‣ Diagnostics ‣ States Dump )

Tip

Since external alias types won’t be touched by OPNsense, you can use pfctl directly in scripts to manage its contents. (e.g. pfctl -t MyAlias -T add 10.0.0.3 to add 10.0.0.3 to MyAlias)

### Internal (automatic)¶

Internal aliases are prefixed with __ so they are easy to identify and can’t overlap with any user defined ones. These aliases help you to determine what the content is for some internal concepts such as “LAN network”. Using the Firewall->Diagnostics->Aliases menu item you can inspect their contents at any time.

## Using Aliases in Firewall Rules¶

Aliases can be used in firewall rules to ease administration of large lists. For instance we might need a list of remote IP addresses that should have access to certain services, when anything changes we only need to update the list.

Let’s create a simple alias to allow 3 remote IP addresses access to an ipsec server for a site to site tunnel connection:

• 192.168.100.1

• 192.168.200.2

• 192.168.202.2

We call our list remote_ipsec and update our firewall rules accordingly.

Note

The list icon identifies a rule with an alias.

## Export / Import¶

The alias admin page (Firewall ‣ Aliases) contains a download and an upload button in the footer of the table, with this feature you can merge aliases into the configuration and download a json formatted list of all aliases in the system.

Since data is validated before insertion, it shouldn’t be possible to import defective data (if the import fails, a list of errors is presented).

Tip

When performing migrations, sometimes its easier to change multiple items at once in a text editor. This feature can easily be used to facilitate that, with limiting risk of a broken configuration (since items are validated equally as single item input would do).

## Add new entries using our API¶

The endpoints from the alias_util can easily be used to push new entries into an alias (or remove existing ones). In case of an external alias these items won’t be persistent over reboots, which can be practical in some use-cases (large frequent changing lists for example).

The document “Use the API” contains the steps needed to create an api key and secret, next you can just call the same endpoint the user interface would.

Below you see how to add 10.0.0.2 to an alias named MyAlias using an insecure connection (self-signed cert) on the host opnsense.firewall with curl. The verbose option provides more details about the data exchanged between the two machines.

curl \
--basic \
--user "key:secret" \
--request POST \
--insecure \
--verbose \


Note

Adding aliases using /api/firewall/alias_util/add/ is only supported for Host, Network and External type aliases

## Exclusions¶

Pf firewall tables support exceptions (or exclusion) of addresses. This feature can be used in one Alias or in combined (Network group type) Aliases. See (https://www.freebsd.org/doc/handbook/firewalls-pf.html 30.3.2.4).

## Nesting¶

For host and network alias types nesting is possibility, this can simplify management a lot since single items can be named properly and grouped into sections for administration.

For example, we define 4 servers among 2 critical using different rulesets:

• server_a {10.0.1.1}

• server_b {10.0.1.2}

• server_c {10.0.1.100}

• server_d {10.0.1.200}

• critical_servers {server_a , server_b}

• other_servers {server_c , server_d}

• servers { critical_servers , other_servers}.

The alias servers will contain all 4 addresses after configuration.

There is also a possibility to combine different Aliases with Aliases, consisting of exclusions. For example, there is Alias “FireHOL” that use extensive externl drop-list and two Aliases that contains subnet and hosts exclusions. It is possible to create Network group (combined) Alias (“FireHOL_with_exclusions”):

• subnets_exclusions {!127.0.0.0/8, !0.0.0.0/8}

• hosts_exclusions {!8.8.8.8}

• FireHOL_with_exclusions {FireHOL, subnets_exclusions, hosts_exclusions}

FireHOL_with_exclusions Alias will contain all records from FireHOL Alias excluding addresses from exclusions Aliases.

It’s always good to check if an address is included in the Alias via Firewall ‣ Diagnostics ‣ pfTable

## Spamhaus¶

The Spamhaus Don’t Route Or Peer Lists DROP (Don’t Route Or Peer) and EDROP are advisory “drop all traffic” lists, consisting of netblocks that are “hijacked” or leased by professional spam or cyber-crime operations (used for dissemination of malware, trojan downloaders, botnet controllers). The DROP and EDROP lists are a tiny subset of the SBL, designed for use by firewalls and routing equipment to filter out the malicious traffic from these netblocks.

Source : https://www.spamhaus.org/drop/