If a client has two dns servers , client will sent dns query to which dns server.

 When a client has two DNS (Domain Name System) servers configured, the decision on which DNS server to send a query to depends on the client's DNS resolution behavior. There are different methods that clients may use to determine which DNS server to query:

 

1. **Primary-Secondary Configuration:**

   - Some clients are configured with primary and secondary DNS servers. In this setup, the client sends the DNS query to the primary DNS server first. If the primary server is unavailable or does not respond within a certain timeout, the client switches to the secondary DNS server.

 

2. **Round Robin:**

   - Some clients use a round-robin approach, alternating between the configured DNS servers for each new DNS query. This helps distribute the load evenly between the DNS servers.

 

3. **Parallel Queries:**

   - Some modern DNS clients can perform parallel queries to multiple DNS servers simultaneously. The client sends the DNS query to all configured DNS servers at the same time and uses the response from the fastest or first-responding server.

 

4. **Response Time-Based Selection:**

   - Some DNS clients may dynamically adjust the selection of DNS servers based on their response times. The client monitors the response times of configured DNS servers and prefers the servers with faster response times.

 

5. **Random Selection:**

   - In some cases, clients may randomly choose one of the configured DNS servers for each query. This approach aims to balance the load across multiple servers.

 

6. **DNS Server Priority:**

   - Some clients may be configured with a priority or preference for each DNS server. The client sends DNS queries to the server with the highest priority first and switches to servers with lower priority if the preferred server is unavailable.

 

The specific behavior depends on the DNS client implementation and configuration. Additionally, the operating system and network settings may influence the DNS server selection process.

 

It's essential to check the documentation or configuration settings of the client's operating system or DNS resolver software to understand the exact behavior in a given scenario.

 

 

if client sends query to first dns server and server did not respond , sends a query to second dns server . Before the second dns server responds now , first dns server replied . Which response client will honour?

 

When a client sends a DNS query to multiple DNS servers sequentially (such as trying the first server and then, if it doesn't respond, trying the second server), the behavior depends on the DNS client implementation and its response handling strategy. Here are a few possibilities:

 

1. **First-Come-First-Serve:**

   - Some DNS clients may honor the first response they receive. If the first DNS server responds before the second server, the client might consider the first response and ignore subsequent responses.

 

2. **Fastest Response:**

   - Some DNS clients prioritize the fastest or quickest response. If the second DNS server responds more quickly than the first one, the client might choose to honor the response from the second server, even if it arrives after the first response.

 

3. **First Successful Response:**

   - The client may honor the first response that is successful (i.e., provides a valid DNS resolution). If the first server responds with a valid resolution, the client might use that response and ignore subsequent responses.

 

4. **Timeouts and Retries:**

   - The DNS client might have a timeout mechanism, and it may retry the first DNS server if it initially did not respond within a specified time. In this case, the client could receive a response from the first server after a retry.

 

5. **Load Balancing or Random Selection:**

   - Some DNS clients may use load balancing or random selection strategies. In such cases, the client might randomly select one of the responding servers or use a load-balancing algorithm to distribute queries.

 

It's important to note that DNS clients may have different implementations, and their behavior in such scenarios may vary. The client's behavior could also be influenced by its configuration settings, the operating system's DNS resolution strategy, and any specific policies or algorithms implemented by the DNS resolver.

 

To understand the exact behavior in a particular case, you may need to refer to the documentation of the DNS client software or the operating system's DNS resolution mechanism in use.