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Configure DNSSEC for a zone for which the Citrix ADC is a DNS proxy server

September 14, 2021
Contributed by: 
S C

The procedure for signing a zone for which the Citrix ADC is configured as a DNS proxy server depends on whether the ADC owns a subset of the zone information owned by the back-end name servers. If it does, the configuration is considered a partial zone ownership configuration. If the ADC does not own a subset of the zone information, the Citrix ADC configuration for managing the back-end servers is considered a zone-less DNS proxy server configuration. The basic DNSSEC configuration tasks for both Citrix ADC configurations are the same. However, signing the partial zone on the Citrix ADC requires some additional configuration steps.

Note: The terms zone-less proxy server configuration and partial zone are used only in the context of the Citrix ADC appliance.

Important: When configured in proxy mode, the ADC does not perform signature verification on DNSSEC responses before updating the cache.

If you configure the ADC as a DNS proxy to load balance DNSSEC aware resolvers (servers), you must set the Recursion Available option while configuring the DNS virtual server. If a DNSSEC query arrives with Checking Disabled (CD) bit set, the query is passed on to the server with the CD bit retained. The response from the server is not cached.

Configure DNSSEC for a zone-less DNS proxy server configuration

For a zone-less DNS proxy server configuration, zone signing must be performed on the back-end name servers. On the Citrix ADC, you configure the ADC as a DNS proxy server for the zone. Create a load balancing virtual server of protocol type DNS. Configure services on the ADC to represent the name servers. Then bind the services to the load balancing virtual server. For more information about these configuration tasks, see Configure the NetScaler as a DNS proxy server.

When a client sends the ADC a DNS request with the DNSSEC OK (DO) bit set, the ADC checks its cache for the requested information. If the resource records are not available in its cache, the ADC forwards the request to one of the DNS name servers. Then, it relays the response from the name server to the client. Also, the ADC caches the RRSIG resource records along with the response from the name server. Subsequent requests from DNSSEC-aware clients are served from the cache (including the RRSIG resource records), subject to the time-to-live (TTL) parameter. If a client sends a DNS request without setting the DO bit, the ADC responds with only the requested resource records. It does not include the RRSIG resource records that are specific to DNSSEC.

Configure DNSSEC for a partial zone ownership configuration

In some ADC configurations, even though the authority for a zone lies with the back-end name servers, a subset of the resource records belonging to the zone might be configured on the ADC. The ADC owns (or is authoritative for) only this subset of records. Such a subset of records can be considered to constitute a partial zone on the ADC. The ADC owns the partial zone. All other records are owned by the back-end name servers.

A typical partial zone configuration on the Citrix ADC is seen when:

  • Global Server Load Balancing (GSLB) domains are configured on the ADC
  • The GSLB domains are a part of a zone for which the back-end name servers are authoritative.

Signing a zone that includes only a partial zone on the ADC involves:

  • Including the partial zone information in the back-end name server zone files
  • Signing the zone on the back-end name servers
  • Signing the partial zone on the ADC.

The same key set must be used to sign the zone on the name servers and the partial zone on the ADC.

Sign the zone on the back-end name servers

  1. Include the resource records that are contained in the partial zone, in the zone files of the name servers.
  2. Create keys and use the keys to sign the zone on the back-end name servers.

Sign the partial zone on the Citrix ADC

  1. Create a zone with the name of the zone owned by the back-end name servers. When configuring the partial zone, set the proxyMode parameter to YES. This zone is the partial zone that contains the resource records owned by the ADC.

    For example, if the name of the zone that is configured on the back-end name servers is example.com, you must create a zone named example.com on the ADC. Set the proxyMode parameter to YES. For more information about adding a zone, see Configure a DNS zone.

    Note

    Do not add SOA and NS records for the zone. These records must exist on the ADC for a zone for which the ADC is authoritative.

  2. Import the keys (from one of the back-end name servers) to the ADC and then add them to the /nsconfig/dns/ directory. For more information about how you can import a key and add it to the ADC, see Publish a DNS key in a zone.
  3. Sign the partial zone with the imported keys. When you sign the partial zone with the keys, the ADC generates RRSIG and NSEC records for the resource record sets and individual resource records in the partial zone, respectively. For more information about signing a zone, see sign and unsign a DNS zone.
Configure DNSSEC for a zone for which the Citrix ADC is a DNS proxy server
September 14, 2021
Contributed by: 
S C
September 14, 2021
Contributed by: 
S C

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