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Manual Chapter: Configuring a DNS Zone Proxy
Manual Chapter
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Configuring a DNS Zone Proxy

Overview: Configuring a DNS zone proxy

Within your network, the BIG-IP® system can act as a proxy for an authoritative DNS server. In this case, when the BIG-IP system receives a zone transfer request from a specified list of DNS namservers (clients), the system sends the request to the authoritative DNS server. The server responds with a zone transfer, and the BIG-IP system sends the zone transfer to the client that made the zone transfer request. Optionally, the BIG-IP system can use transaction signature (TSIG) keys to validate the identity of the authoritative DNS server sending a zone transfer and the DNS nameservers (clients) sending zone transfer requests.

Example of DNS zone proxy with client-side TSIG authentication

In this figure, an administrator at Site Request creates a DNS zone on the BIG-IP system that is a proxy for the zone on the authoritative DNS server that hosts the zone. The name of the DNS zone on the BIG-IP system matches the name of the zone on the authoritative DNS server. The administrator uses TSIG key authenthication to verify the zone transfer communications between the BIG-IP system and the DNS nameserver (client) making the zone transfer request.

BIG-IP system acting as DNS zone proxy with client-side TSIG authentication

BIG-IP system acting as DNS zone proxy with client-side TSIG authentication

  1. DNS nameserver (client) sends TSIG-signed zone transfer request for a DNS zone.
  2. BIG-IP system validates the signature and removes the client TSIG key.
  3. BIG-IP system sends the unsigned request to the DNS server that hosts the zone.
  4. DNS server answers with an unsigned zone transfer to the BIG-IP system.
  5. BIG-IP system adds the client TSIG key to the response.
  6. BIG-IP system sends a TSIG-signed zone transfer to the DNS nameserver that made the request.

Example of DNS zone proxy with client-side and server-side TSIG authentication

In this figure, an administrator at Site Request creates a DNS zone on the BIG-IP system that is a proxy for the zone on the authoritative DNS server that hosts the zone. The name of the DNS zone on the BIG-IP system matches the name of the zone on the authoritative DNS server. The administrator uses TSIG key authenthication to verify the zone transfer communications between the BIG-IP system and the authoritative DNS server and between the BIG-IP system and the client making a zone transfer request.

BIG-IP system acting as DNS zone proxy with client and server-side TSIG        authentication

BIG-IP system acting as DNS zone proxy with client and server-side TSIG authentication

  1. DNS nameserver (client) sends TSIG-signed zone transfer request for a DNS zone.
  2. BIG-IP system validates the signature, removes the client TSIG key from the request, and adds the server TSIG key to the request.
  3. BIG-IP system sends the TSIG-signed request to the DNS server that hosts the zone.
  4. DNS server answers with a TSIG-signed zone transfer to the BIG-IP system.
  5. BIG-IP system validates the signature, removes the server TSIG key from the response, and adds the client TSIG key to the response.
  6. BIG-IP system sends the TSIG-signed zone transfer to the DNS nameserver that made the request.

About TSIG key authentication

The BIG-IP® system can use transaction signature (TSIG) keys to authenticate communications about zone transfers between the BIG-IP system and authoritative DNS servers, and between the BIG-IP system and DNS nameservers (clients). TSIG keys are generated by a third party tool such as BIND's keygen utility. Using TSIG keys is optional.

TSIG key configured on authoritative DNS server
You can add a TSIG key to a nameserver object that represents an authoritative DNS server. With this configuration, when the DNS server sends a NOTIFY message to the BIG-IP system, DNS Express™ responds with a TSIG-signed zone transfer request. Then the DNS server returns a TSIG-signed zone transfer. If required, you can disable the Verify Notify TSIG option on the DNS zone. With this configuration, DNS Express can process a NOTIFY message without a TSIG key, even when a subsequent zone transfer requires a TSIG key.
TSIG key configured on DNS nameserver (client)
You can add a TSIG key to a nameserver object that represents a DNS nameserver (client). When the client sends a TSIG-signed zone transfer request, DNS Express returns a TSIG-signed zone transfer.
TSIG key configured on DNS zone
You can add a server TSIG key to a DNS zone on the BIG-IP system. With this configuration, the system uses this TSIG key when the zone on the BIG-IP system is a proxy for the zone on the server. There are two possible scenarios:
  • Client sends TSIG-signed zone transfer request

    When the BIG-IP system receives a TSIG-signed zone transfer request from a client for a DNS zone for which it is a proxy, the system validates the client TSIG key and removes the key from the request. The system then adds the server TSIG key to the request and forwards the TSIG-signed request to the DNS server or load balances the TSIG-signed request to a pool of DNS servers. The DNS server responds with a TSIG-signed zone transfer. The BIG-IP system validates the server TSIG key and removes the key. Then the system adds the client TSIG key and returns a TSIG-signed signed zone transfer to the client.

  • Client sends unsigned zone transfer request

    When the BIG-IP system receives an unsigned zone transfer request from a client for a DNS zone for which it is a proxy, the system adds the server TSIG key to the request. The system then forwards the TSIG-signed request to the DNS server or load balances the TSIG-signed request to a pool of DNS servers. The DNS server responds with a TSIG-signed zone transfer. The BIG-IP system validates the server TSIG key and removes the key. Then the system returns an unsigned zone transfer to the client.

About listeners

A listener is a specialized virtual server that passively checks for DNS packets on port 53 and the IP address you assign to the listener. When a DNS request is sent to the IP address of the listener, the BIG-IP® system either handles the request or forwards the request to the appropriate resource.

Task summary

Perform these tasks to configure a DNS zone on the BIG-IP system that is a proxy for a DNS zone on a DNS server in your network:

Configuring BIND servers to allow zone transfers

If you are unfamiliar with how to modify BIND server files, review the fifth edition of DNS and BIND, available from O’Reilly Media.
Typically, BIND servers allow zone transfers to any DNS nameserver requesting a zone transfer. That is, named.conf on a typical BIND server does not contain an allow-transfer statement. Therefore, adding an allow-transfer statement to a BIND server actually restricts zone transfers to a specified list of DNS nameservers.

When you want the BIG-IP® system to act as a proxy for a DNS zone configured on a BIND server, you must add an allow-transfer statement to named.conf on the BIND server that hosts the zone.

Here is an example allow-transfer statement that you can modify to meet your needs: allow-transfer { localhost; <self IP address on BIG-IP from which zone transfer request is sent to the DNS server>; };
allow-transfer { localhost; 10.10.10.1 ; };

Adding TSIG keys for DNS zone proxy

Obtain the TSIG keys that you want to add to the BIG-IP® system for the DNS server that hosts the zone. Obtain the TSIG key for the DNS nameservers (clients) that you want to add to the BIG-IP system configuration.
Note: TSIG keys are created by a third party tool such as BIND’s keygen utility.

When you want the BIG-IP system to authenticate the identity of the DNS server and DNS nameservers (clients) when communicating about DNS zone transfers, add TSIG keys to the BIG-IP system configuration.

  1. On the Main tab, click DNS > Delivery > Keys > TSIG Key List .
    The TSIG Key List screen opens.
  2. Click Create.
    The New TSIG Key screen opens.
  3. In the Name field, type the name of the TSIG key.
  4. From the Algorithm list, select the algorithm that was used to generate the key.
  5. In the Secret field, type the TSIG key secret.
  6. Click Finished.
  7. Create additional TSIG keys, as needed.
Add the server TSIG key for the DNS server to the DNS zone configured on the BIG-IP system. Add TSIG keys to DNS nameservers (clients) configured on the BIG-IP system.

Adding DNS nameserver (client) objects

Gather the IP addresses of the DNS nameservers (clients) from which the BIG-IP® system accepts zone transfer requests for a DNS zone. Optional: Ensure that the client TSIG key is available on the BIG-IP system.
To allow DNS nameservers (clients) to request zone transfers for a zone, add a nameserver object that represents each client. Optionally, you can add a client TSIG key that the BIG-IP system uses to authenticate the identity of the client during zone transfer communications.
  1. On the Main tab, click DNS > Delivery > Nameservers .
    The Nameservers List screen opens.
  2. Click Create.
    The New Nameserver screen opens.
  3. In the Name field, type a name for the DNS nameserver (client).
  4. In the Address field, type the IP address on which the DNS nameserver (client) listens for DNS messages.
  5. Optional: From the TSIG Key list, select the TSIG key that matches the TSIG key on the DNS nameserver (client).
    The BIG-IP system uses this TSIG key to authenticate zone transfer communications as coming from this client and to sign communications sent to this client.
  6. Click Finished.
  7. Add nameserver objects to represent other DNS nameservers (clients).
Add the DNS nameservers (clients) objects to the Zone Transfer Client list of the DNS zone on the BIG-IP system.

Enabling zone transfers

To enable the BIG-IP system to handle zone transfers, create a custom DNS profile.
  1. On the Main tab, click DNS > Delivery > Profiles > DNS or Local Traffic > Profiles > Services > DNS .
    The DNS profile list screen opens.
  2. Click Create.
    The New DNS Profile screen opens.
  3. In the General Properties area, name the profile dns_zxfr.
  4. Select the Custom check box.
  5. In the DNS Features area, from the DNS Express list, select Disabled.
  6. In the DNS Traffic area, from the Zone Transfer list, select Enabled.
  7. In the DNS Features area, from the Unhandled Query Actions list, select Allow.
    The BIG-IP system forwards zone transfer requests to a DNS server or a member of a pool of DNS servers.
  8. In the DNS Features area, from the Use BIND Server on BIG-IP list, select Disabled.
  9. Click Finished.
Assign the profile to listeners.

Creating a DNS zone

Before you create a DNS zone to serve as a proxy for a zone hosted on a DNS server on your network, do the following:
  • Optional: Ensure that the TSIG key on the DNS server is available on the BIG-IP system.
  • Determine the name you want to use for the DNS zone. The name must exactly match the name on the DNS server that hosts the zone.
    Note: Zone names are case insensitive.
When you want the BIG-IP system to act as a proxy for a zone hosted on a DNS server on your network, create a DNS zone and associate the server TSIG key on the DNS server with the zone on the BIG-IP system.
  1. On the Main tab, click DNS > Zones .
    The Zone List screen opens.
  2. Click Create.
    The New Zone screen opens.
  3. In the Name field, type the name of the DNS zone.
    The name must begin and end with a letter and contain only letters, numbers, and the period and hyphen (-) characters.
  4. In the Zone Transfer Clients area, move the nameservers that can initiate zone transfers from the Available list to the Active list.
  5. Optional: From the Server Key list, select the TSIG key that matches the TSIG key on the DNS server.
    The BIG-IP system uses this TSIG key to sign DNS zone transfer requests, before forwarding the requests to the DNS server that hosts this zone, and then to verify a zone transfer returned from the DNS server.
  6. Click Finished.

Creating listeners to forward zone transfer requests

Determine to which DNS server you want the listeners to forward DNS zone transfer requests.

Create listeners to alert the BIG-IP® system to zone transfer requests destined for a DNS server that hosts the zone. Create two listeners that use the TCP protocol, one each for an IPv4 address and IPv6 address.

Note: DNS zone transfers use TCP port 53.
Note: This task applies only to GTM™-provisioned systems.
  1. On the Main tab, click DNS > Delivery > Listeners .
    The Listeners List screen opens.
  2. Click Create.
    The Listeners properties screen opens.
  3. In the Name field, type a unique name for the listener.
  4. For the Destination setting, in the Address field, type the IPv4 address on which the BIG-IP system listens for DNS zone transfer requests for a zone hosted on a DNS server.
  5. From the Listener list, select Advanced.
  6. From the VLAN Traffic list, select All VLANs.
  7. Optional: If you are using SNATs on your network, from the Source Address Translation list, select SNAT.
  8. Optional: If you are using NATs on your network, for the Address Translation setting, select the Enabled check box.
  9. Optional: If you are using port translation on your network, for the Port Translation setting, select the Enabled check box.
  10. In the Service area, from the DNS Profile list, select dns_zxfr (the custom profile you created to enable the BIG-IP system to process zone transfer requests).
  11. In the Service area, from the Protocol list, select TCP.
  12. Click Repeat.
  13. Create another listener with the same settings, except using an IPv6 address.
  14. Click Finished.

Creating virtual servers to forward zone transfer requests

Determine to which DNS server you want the virtual servers to forward DNS zone transfer requests.

Create virtual servers to alert the BIG-IP system to zone transfer requests destined for a DNS server that hosts the zone. Create two virtual servers that use the TCP protocol, one each for an IPv4 address and IPv6 address.

Note: DNS zone transfers use port 53.
Note: This task applies only to LTM®-provisioned systems.
  1. On the Main tab, click Local Traffic > Virtual Servers .
    The Virtual Server List screen opens.
  2. Click the Create button.
    The New Virtual Server screen opens.
  3. In the Name field, type a unique name for the virtual server.
  4. In the Destination Address field, type the IP address in CIDR format.
    The supported format is address/prefix, where the prefix length is in bits. For example, an IPv4 address/prefix is 10.0.0.1 or 10.0.0.0/24, and an IPv6 address/prefix is ffe1::0020/64 or 2001:ed8:77b5:2:10:10:100:42/64. When you use an IPv4 address without specifying a prefix, the BIG-IP® system automatically uses a /32 prefix.
    Note: The IP address for this field needs to be on the same subnet as the external self-IP.
  5. In the Service Port field, type 53.
  6. From the Protocol list, select TCP.
  7. Optional: If you are using SNATs on your network, from the Source Address Translation list, select SNAT.
  8. Optional: From the SNAT pool list, select the name of an existing SNAT pool.
  9. From the Configuration list, select Advanced.
  10. From the DNS Profile list, select the custom DNS profile you created.
  11. Click Finished.
Create another virtual server with the TCP protocol, but use an IPv6 address and configuration.
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