Configure the Citrix ADC as an ADNS server

January 6, 2021

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You can configure the ADC appliance to function as an authoritative domain name server (ADNS) for a domain. As an ADNS server for a domain, the Citrix ADC resolves DNS requests for all types of DNS records that belong to the domain. To configure the Citrix ADC to function as an ADNS server for a domain, you must create an ADNS service and configure NS and Address records for the domain on the Citrix ADC. The ADNS service can be configured using the subnet IP address (SNIP) or a separate IP address. The following topology diagram shows a sample configuration and the flow of requests and responses.

Figure 1. Citrix ADC as an ADNS

The following table shows the parameters that are configured for the ADNS service illustrated in the preceding topology diagram.

Entity type
Name
IP address
Type
Port

ADNS Service
Service-ADNS-1
10.102.29.51
ADNS
53

Table 1. Example of ADNS Service Configuration

To configure an ADNS setup, you must configure the ADNS service. For instructions on configuring the ADNS service, see Load balancing.

During DNS resolution, the ADNS server directs the DNS proxy or local DNS server to query the Citrix ADC for the IP address of the domain. Because the Citrix ADC is authoritative for the domain, it sends the IP address to the DNS proxy or local DNS server. The following diagram describes the placement and role of the ADNS server in a GSLB configuration.

Figure 2. GSLB Entity Model

Note: In ADNS mode, if you remove SOA and ADNS records, the following do not function for the domain hosted by the Citrix ADC: ANY query (for more information about the ANY query, see DNS ANY query), and negative responses, such as NODATA and NXDOMAIN.

Create an ADNS service

An ADNS service is used for global service load balancing. For more information about creating a GSLB setup, see Global server load balancing. You can add, modify, enable, disable, and remove an ADNS service. For instructions on creating an ADNS service, see Configure services.

Note: You can configure the ADNS service to use SNIP or any new IP address.

When you create an ADNS service, the Citrix ADC responds to DNS queries on the configured ADNS service IP and port.

You can verify the configuration by viewing the properties of the ADNS service. You can view properties such as name, state, IP address, port, protocol, and maximum client connections.

Configure the ADNS setup to use TCP

By default, some clients use the User Datagram Protocol (UDP) for DNS, which specifies a limit of 512 bytes for the payload length of UDP packets. To handle payloads that exceed 512 bytes in size, the client must use TCP. To enable DNS communications over TCP, you must configure the Citrix ADC appliance to use the TCP protocol for DNS. The Citrix ADC then sets the truncation bit in the DNS response packets. The truncation bit specifies that the response is too large for UDP and that the client must send the request over a TCP connection. The client then uses the TCP protocol on port 53 and opens a new connection to the Citrix ADC. The Citrix ADC listens on port 53 with the IP address of the ADNS service to accept the new TCP connections from the client.

To configure the Citrix ADC to use the TCP protocol, you must configure an ADNS_TCP service. For instructions on creating an ADNS_TCP service, see Load balancing.

Important

To configure the Citrix ADC to use UDP for DNS and use TCP only when the payload length of UDP exceeds 512 bytes, you need to configure the ADNS and ADNS_TCP services. The IP address of the ADNS_TCP service must be the same as the IP address of the ADNS service.

Add DNS resource records

After you create an ADNS service, you can add DNS records. For instructions on adding DNS records, see Configure DNS resource records.

Remove ADNS services

For instructions on removing services, see Load balancing

Configure domain delegation

Domain delegation is the process of assigning responsibility for a part of the domain space to another name server. Therefore, during domain delegation, the responsibility for responding to the query is delegated to another DNS server. Delegation uses NS records.

In the following example, sub1.abc.com is the subdomain for abc.com. The procedure describes the steps to delegate the subdomain to the name server ns2.sub1.abc.com and add an Address record for ns2.sub1.abc.com.

To configure domain delegation, you need to perform the following tasks, which are described in the sections that follow:

1. Create an SOA record for a domain.
2. Create an NS record to add a name server for the domain.
3. Create an Address record for the name server.
4. Create an NS record to delegate the subdomain.
5. Create a glue record for the name server.

Create an SOA record

For instructions on configuring SOA records, see Create SOA records for authoritative information.

Create an NS record for a name server

For instructions on configuring an NS record, see Create NS records for an authoritative server. In the Name Server list, select the primary authoritative name server, for example, ns1.abc.com.

Create an address record

For instructions on configuring Address records, see Create address records for a domain name. In the Host Name and IP address text boxes, type the domain name for the DNS Address record and the IP address, for example, ns1.abc.com and 10.102.11.135, respectively.

Create an NS record for domain delegation

For instructions on configuring NS records, see Create NS records for an authoritative server. In the Name Server list, select the primary authoritative name server, for example, ns2.sub1.abc.com.

Create a glue record

NS records are typically defined immediately after the SOA record (not a restriction.) A domain must have at least two NS records. If an NS record is defined within a domain, it must have a matching Address record. This Address record is referred to as a glue record. Glue records speed up DNS queries.

For instructions on adding glue records for a subdomain, see the procedure for adding an Address (A) record, Configure DNS resource records.

For instructions on configuring Address records, see Create address records for a domain name. In the Host Name and IP address text boxes, type the domain name for the DNS Address record and the IP address, for example, ns2.sub1.abc.com and 10.102.12.135, respectively.