What will be the effect of binding a responder action that creates a DNS response with TC bit set and rcode NOERROR?

• A. Set TC bit and rcode as NOERROR in the DNS Request from Client
• B. Set TC bit and rcode as NOERROR in the DNS Response from DNS server
• C. Create a DNS Response with TC bit set and rcode as NOERROR
• D. Create a DNS Request with TC bit set and rcode as NOERROR

Answer: (C)

The effect is to generate a DNS response that carries a truncated answer with no error in processing. The TC bit in the DNS header indicates the response was too large to fit in a single UDP packet, so the data is incomplete. The rcode NOERROR shows that the server processed the query successfully; there isn’t an error to report. In practice, the client will know to retry over TCP (or with EDNS) to obtain the full answer. This action is about creating a response message, not modifying a request or producing a new request.