30.12. Configuring Forwarding and Transfers

BIND can be configured to forward all requests for zones that it is not the master or slave for to another DNS server. When doing this, it acts like a DNS client itself, accepting requests from real clients and then sending them off to another server or servers for resolution instead of carrying out the normal process of contacting the root zone servers and finding the correct server for the domain. This can be useful if your DNS server is unable to contact the rest of the Internet, but can still communicate with a DNS server that does have full network access. For example, it may be on an internal network behind a firewall that only allows connections to a limited set of destinations.

To set up forwarding, the steps to follow are:

1.
On the module's main page, click on the Forwarding and Transfers icon.

2.
In the form that appears, fill in the Servers to forward queries to field with the IP addresses of DNS servers that requests should be sent to. BIND will try them in order until one returns a positive or negative a response.

If the list is empty, the server will revert to the normal method of looking up records by contacting the root servers and so on.

3.
If you want your server to attempt to resolve a client's query directly when it cannot contact any of the forwarding servers, set the Lookup directly if no response from forwarder field to Yes. This is only useful if your server is actually capable of doing lookups.

4.
Click the Save button at the bottom of the page, and then hit Apply Changes back on the main page to make the new setting active. Assuming the forwarding list was filled in, your server will now send all client queries to the listed servers.

The same form also contains fields for configuring BIND's behavior when doing zone transfers. You can control how long it will wait for a transfer to complete, the protocol used for transfers and the number that can be active at the same time. To edit these settings, follow these steps:

1.
On the module's main page, click on the Forwarding and Transfers icon.

2.
By default, BIND will wait 120 minutes (2 hours) for a zone transfer from a master to complete. To change this, enter a different number of minutes into the Maximum zone transfer time field. This can also be set or overridden on a per-slave zone basis.

3.
BIND versions before 8.1 only support the transfer of a single zone at a time. Because this can be slow when transferring many zones from the same master server, the Zone transfer format field can be set to Many to use a new format that combines multiple domains into the same transfer. If One at a time or Default is chosen, then each zone will be transferred separately. This is the best choice unless you are sure that all slave servers are running BIND 8.1 or above.

4.
By default, your name server will not carry out more than 2 concurrent zone transfers from the same master server. To increase this limit, change the Maximum concurrent zone transfers field to something higher. This can speed up the process of transferring a large number of domains, but at the expense of putting a higher load on the master server.

5.
Click the Save button when you are done making changes and then click Apply Changes on the main page to activate them. The new settings will apply to all subsequent zone transfers.

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