DNS Views allow a name server to segregate the data and provide a different view of the data based on the clients accessing it. When DNS receives a DNS request, the request is processed to associate it with a DNS view. The association is performed by matching the client source and/or destination address to the source and destination ACLs configured on the view. Views are matched in priority order with the lowest non-zero priority being matched first. Once a request is matched to a DNS View, only the data in that view is available to the request. There is a one-to-one mapping between zones and views—a zone can only exist in one view. If the zone must exist in more than one view, make copies of the zone and associate with different views.

If you have an interval view and an external view, a typical setup is to set the priority of the internal view to one and set the ACLs (typically acl-match-clients) to match the criteria for internal clients. For the external view, leaving the default priority and ACLs will allow all requests not matching the interval view to match the external view.

Note	Getting a NOTAUTH rcode response when DNS Views are configured, typically indicates that the request matched a view where the zone does not exist.

Note	The auto-view detection is only applicable for Cisco Prime Network Registrar servers.

Views for the DNS client servers such as Caching DNS, Secondary DNS, Primary for Notifies, DHCP, and so on, are easily defined with minimal configuration.

Views that do not have any associated zones are still processed and may leave clients associated with empty views. Therefore, it is important to avoid creating views that are not being used.

Following are some of the key points or attributes to know while working on DNS Views:

• View ID—Defines a unique integer identifier for the view that is assigned by the CCM server or the user while creating DNS views.
• View Priority (priority attribute)—Each DNS View is assigned a unique priority to determine the view processing order. The lowest non-zero priority is processed first, followed by the second lowest, and so on. A zero priority is reserved for the Default view, which is always processed last. The web UI provides a mechanism to reorder views without explicitly setting the priority.
• Default View—The default view is created with view-id=0, priority=0, and client and destination ACLs set to any. Requests that do not match a named view always falls into the default view. By default, zones are created with a view-id=0, which automatically places them in the default view. The default view cannot be modified or deleted.
• acl-match-clients attribute—Specifies the ACLs that map clients to a view based on the client source address. The default is any and must be modified in order to have the clients associated with the appropriate views.

• acl-match-destinations (Expert mode attribute)—Specifies the ACLs that map clients to a view based on the client destination address. The default is any and should only be changed if the DNS server is using different network interfaces for different views.

• The Cisco Prime Network Registrar Caching DNS server can associate the client requests to the appropriate views on behalf of the Authoritative DNS server. This is done by configuring the DNS Views on the Caching DNS server and setting the uses-views attribute on the List/Add Exceptions page to true. The Caching DNS server maps the client to the appropriate view and tag the queries forwarded to the Authoritative DNS server with the appropriate view. Therefore, in these cases, the view mapping is done by the Caching DNS server.

  Note	The Caching DNS server only maps clients to acl-match-clients. The acl-match-destinations attribute is ignored.

  DNS Views and Exception settings are automatically synced/set by zone distribution.

Zone distribution sync, single zone sync, and HA DNS zone sync will always sync associated views and named ACLs for both primary and secondary zones. The synchronization modes applied while running zone distribution or HA DNS sync vary. When you run:

• Zone Distribution Sync—views will be synchronized in Replace mode for all zone distribution sync types (Update, Complete, and Exact), while ACLs will use Ensure mode. If caching DNS servers are included in the zone distribution, the associated views and named ACLs will be synchronized to these servers and the masters list will be configured as exceptions for the unique set of domain names in the distribution. The user must exclude secondaries and/or caching servers.
• HA DNS Sync—views will be updated in Replace mode for both Update and Complete sync, while Exact sync will sync views in Exact mode.

You can also push views and ACLs to and pull views and ACLs from the regional cluster in Ensure, Replace, and Exact modes.