Tags and Views

The tags and views functionality make it possible to send specific DNS answers based on the IP address of the client.

Tags

The tags functionality makes it possible to divide client source addresses in categories (tags), and use local-zone and local-data information for these specific tags.

Before these tags can be used, you need to define them in the Unbound configuration using define-tags. In this example, a tag for domains containing malware is set, along with one for domains of gambling sites:

define-tags: "malware gambling"

Now that Unbound is aware of the existing tags, it is possible to start using them. The access-control-tag element is used to specify the tag to use for a client addresses. You can add multiple tags to an access-control element:

access-control-tag: 10.0.1.0/24 "malware"
access-control-tag: 10.0.2.0/24 "malware"
access-control-tag: 10.0.3.0/24 "gambling"
access-control-tag: 10.0.4.0/24 "malware gambling"

Unbound will create an access-control-tag element with the “allow” type if the IP address block in the access-control-tag element does not match an existing access-control.

When a query comes in from an address with a tag, Unbound starts searching its local-zone tree for the best match. The best match is the most specific local-zone with a matching tag, or without any tag. That means that local-zones without any tag will be used for all clients and tagged local-zones only for clients with matching tags.

Adding tags to local-zones can be done using the local-zone-tag element:

local-zone: malwarehere.example refuse
local-zone: somegamblingsite.example static
local-zone: matchestwotags.example transparent
local-zone: notags.example inform

local-zone-tag: malwarehere.example malware
local-zone-tag: somegamblingsite.example malware
local-zone-tag: matchestwotags.example "malware gambling"

A local-zone can have multiple tags, as illustrated in the example above. The tagged local-zones will be used if one or more tags match the client. So, the matchestwotags.example local-zone will be used for all clients with at least the malware or gambling tag. The used local-zone type will be the type specified in the matching local-zone. It is possible to depend the local-zone type on the client address and tag combination. Setting tag specific local-zone types can be done using access-control-tag-action:

access-control-tag-action: 10.0.1.0/24 "malware" refuse
access-control-tag-action: 10.0.2.0/24 "malware" deny

In addition to configuring a local-zone type for some specific client address/tag match, it is also possible to set the used local-data RRs. This can be done using the access-control-tag-data element:

access-control-tag-data: 10.0.4.0/24 "gambling" "A 127.0.0.1"

Sometimes you might want to override a local-zone type for a specific IP address block, regardless the type configured for tagged and untagged local zones, and regardless the type configured using access-control-tag action. This override can be done using local-zone-override.

Views

Tags make is possible to divide a large number of local-zones in categories, and assign these categories to a large number of IP address blocks. As tags on the IP address blocks and local-zones are stored in bitmaps, it is advised to keep the number of tags low. If a lot of clients have their own local-zones, without sharing these to other IP address blocks, it can result a large amount tags. In this situation is is more convenient to give the client’s IP address block its own tree containing local-zones. Another benefit of having a separate local zone tree is that it makes it possible to apply a local-zone action to a part of the domain space, without having other local-zone elements of subdomains overriding this. Configuring a client specific local-zone tree can be done using views.

A view is a named list of configuration options. The supported view configuration options are local-zone and local-data.

A view is configured using a view clause. There may be multiple view clauses, each with a unique name. For example:

view:
    name: "firstview"
    local-zone: example.com inform
    local-data: 'example.com TXT "this is an example"'
    local-zone: refused.example.nl refuse

Mapping a view to a client can be done using the access-control-view element:

access-control-view: 10.0.5.0/24 firstview

By default, view configuration options override the global configuration outside the view. When a client matches a view it will only use the view’s local-zone tree. This behaviour can be changed by setting view-first to yes. If view-first is enabled, Unbound will try to use the view’s local-zone tree, and if there is no match it will search the global tree.