A Citrix Administrator configured the Citrix ADC as a DNS Proxy Server and applied a rewrite action to set the AA bit in the DNS header. What will be the effect on the DNS messages?

• A. Unset the AA bit of DNS Request
• B. Set the AA bit of DNS Response
• C. Unset the AA bit of DNS Response
• D. Set the AA bit in DNS Request

Answer: (B)

The AA bit represents the Authoritative Answer flag in the DNS header and is meaningful only in responses. It indicates that the responding server is authoritative for the queried name. Queries don’t carry this bit, so there’s nothing to unset there.

By applying a rewrite action to set the AA bit, the Citrix ADC will modify the DNS response as it flows back to the client, marking that response as authoritative. It does not affect the request going from the client to the upstream server, and it does not make sense to set the AA bit on a request. So the observable effect is that the DNS response sent to the client will have the AA bit set.