This command enters DNS view list configuration mode--for the specified view list--so that individual view list members (DNS views and their order numbers within the view list) can be accessed in, added to, or deleted from that view list. If the specified DNS view list does not exist yet, it is automatically created.
The maximum number of DNS views and view lists supported is not specifically limited but is dependent on the amount of memory on the Cisco router. Configuring a larger number of DNS views and view lists uses more router memory, and configuring a larger number of views in the view lists uses more router processor time. For optimum performance, configure no more views and view list members than needed to support your Split DNS query forwarding or query resolution needs.
To display information about a specific DNS view list or all currently configured DNS view lists, use the show ip dns view-list command.
Subsequent Operations on a DNS View List
After you use the ip dns view-list command to define a DNS view list and enter DNS view list configuration mode, you can use the view command to access a view list member or add a DNS view as a new view list member at the end of the list. Each view list member specifies a DNS view and a value that indicates the relative order for checking that view when the DNS view list is used. to determine if it can be used to address a DNS query.
For any DNS view list member, you can use the restrict authenticated, restrict name-group, and restrict source access-group commands to configure usage restrictions for the DNS view list member. These restrictions are based on query source authentication, the query hostname, and the query source host IP address, respectively.
Purpose of a DNS View List
When a DNS view list is used to select a DNS view to use to handle a given DNS query, the Cisco IOS software checks each DNS view in the DNS view list--in the order specified in the view list--to determine if the usage restrictions for that view allow the view to be used to address that particular DNS query.
The first DNS view with configured usage restrictions that allow its use for the DNS query will be used to resolve or forward the query. That is, the router will use the configuration parameters for that DNS view to either respond to the query (by using the name cache belonging to the DNS view) or forward the query to the configured name servers. If no DNS view in the view list is qualified to handle the query, the router does not send or forward the query.
Multiple DNS view list definitions enable you to use the same DNS view, but with different restrictions, depending on the source of the DNS query being processed. For example, in one DNS view list a particular DNS view could be used with very few usage restrictions, while in another DNS view list the same DNS view could be used with more usage restrictions.
Use of a DNS View List for DNS Queries Incoming from a Particular Interface
Use the ip dns view-group command to configure the router to use a particular DNS view list to determine which DNS view to use to handle incoming DNS queries that arrive on that interface. Only one DNS view list can be assigned to a given interface. However, a single DNS view list can be assigned to any number of interfaces so that the same ordered list of DNS views (along with the restrictions specified in the view list) can be checked by multiple interfaces.
Use of a DNS View List as the Default DNS View List
Use the ip dns server view-list command to configure the default DNS view list. The router uses the default DNS view list to determine which DNS view to use to handle incoming DNS queries that arrive on an interface that is not configured with a DNS view list.