Which two types of attacks are typically used on DNS open resolvers? (Choose two.)

The choice of amplification and reflection attacks as the correct answer highlights the vulnerabilities associated with DNS open resolvers. These attacks exploit the way DNS operates, particularly when open resolvers are misconfigured to respond to requests from any source on the internet.

In an amplification attack, an attacker sends a small query to a DNS resolver that results in a much larger response being sent to the targeted victim's address. This is possible due to the inherent nature of DNS, where a single query can produce a significantly larger reply, often many times greater in size than the original request. This can overwhelm the victim's network resources.

Reflection attacks, similarly, involve an attacker sending a request to a DNS server with the source address spoofed to that of the intended victim. The DNS server responds to what it believes is a legitimate query but actually sends that response to the victim. This can also lead to network congestion and denial of service.

These two attack types are particularly relevant to DNS open resolvers because they highlight how DNS can be misused if strict security measures are not implemented. Open resolvers that accept and respond to queries from any source can easily become targets for these forms of abuse, making it critical for administrators to configure DNS servers to limit who can query them.