How to Configure your DNS server to limit the number of queries

Configuring your DNS server to limit the number of queries can help protect it from abuse and DNS amplification attacks. By implementing query rate limiting, you can restrict the number of queries that a specific client or IP address can make within a certain time frame. Here’s how you can configure query rate limiting on popular DNS servers:

1. BIND DNS Server:

BIND (Berkeley Internet Name Domain) is one of the most commonly used DNS server software. To configure query rate limiting in BIND, follow these steps:

  • Edit your BIND configuration file (usually named named.conf or named.conf.options).
  • Add the following lines to the configuration file:
shell
options {
    ...
    rate-limit {
        responses-per-second 5;  # Adjust the limit to your preference
        window 5;                # Adjust the time window in seconds
    };
};
  • responses-per-second: Specifies the maximum number of responses allowed from a client per second.
  • window: Defines the time window in seconds during which the specified number of responses is allowed.

2. Microsoft DNS Server (Windows Server):

If you’re using the Microsoft DNS Server on Windows Server, you can configure query rate limiting using PowerShell. Here’s how:

  • Open PowerShell as an administrator.
  • Run the following command to configure query rate limiting:
powershell
Set-DnsServerResponseRateLimiting -EnableResponseRateLimiting $true -Window [time_in_seconds] -SlidingExpiration $true -MaxWindowSize [max_responses]
  • Window: Specifies the time window in seconds during which the rate limiting is applied.
  • -SlidingExpiration: When set to $true, allows the counter to reset for each time window.
  • -MaxWindowSize: Specifies the maximum number of responses allowed during the specified time window.

3. dnsmasq:

Dnsmasq is a lightweight DNS and DHCP server. To configure query rate limiting in dnsmasq, follow these steps:

  • Edit your dnsmasq configuration file (usually located at /etc/dnsmasq.conf).
  • Add the following lines to limit the query rate:
shell
--dns-forward-max=100          # Adjust the maximum number of DNS queries allowed
--dns-forward-max-retries=3    # Adjust the number of retries
--dns-forward-strict-order     # Enforce strict DNS query order
  • --dns-forward-max: Specifies the maximum number of DNS queries allowed within the specified time frame.
  • --dns-forward-max-retries: Defines the number of retries allowed for each query.
  • --dns-forward-strict-order: Enforces strict DNS query order.

Keep in mind that these configurations are just examples, and you should adjust the values according to your specific needs and the expected query rate for your DNS server. Additionally, it’s essential to regularly monitor your DNS server’s logs and performance to ensure that legitimate queries are not being affected by the rate-limiting settings.