Affected products
Public DNS is a global public recursive domain name resolution service available to all internet users. This rate limiting notice only affects the Public DNS Free Edition (223.5.5.5, 223.6.6.6, and others). It does not apply to domain registration, DNS record configuration, or the public authoritative DNS service. The authoritative resolution service remains unchanged.
Affected users
This notice affects users of the Public DNS Free Edition, including traffic sent over DNS over HTTPS (DoH), DNS over TLS (DoT), UDP, and TCP. It does not apply to the Alibaba Cloud public authoritative DNS service, whose business logic remains unchanged.
Effective date
Effective from 24:00 on September 30, 2024
Details
Starting September 30, 2024, Alibaba Cloud applies intelligent traffic control to resolution requests on the Public DNS Free Edition (223.5.5.5, 223.6.6.6, and others) to protect system stability.
For most free users, service continues without interruption. In high-concurrency scenarios that risk system stability, the service may temporarily limit concurrent requests from a single source IP to a single recursive node. When rate limiting is triggered, affected queries may experience increased latency or temporary failures — the service does not hard-stop, but no availability guarantee applies. The concurrency limit is not a fixed threshold: the system adjusts it dynamically based on network load and overall service quality. The Public DNS Free Edition does not offer a Service Level Agreement (SLA).
Solutions
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Enable local DNS caching to reduce the number of outbound resolution requests.
On Linux systems, enable the nscd (Name Service Cache Daemon) caching service.
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Enterprise customers with high request volumes who need a guaranteed SLA should upgrade to the Public DNS Paid Edition.
The Public DNS Paid Edition offers a Service Level Agreement (SLA) with 99.99% service availability for resolution, and its users are not subject to rate limiting. The following promotional offers are available for the paid edition:
For users connecting via DoH/DoT: The Public DNS Paid Edition provides 10 million free HTTP queries per month to all customers, which meets the daily needs of most small enterprise applications. For usage above the free quota, both pay-as-you-go and data transfer plan billing models are available. For details, see Billing.
For users connecting via UDP/TCP: Protect high-volume requests from rate limiting by attaching a public egress IP address. In extreme scenarios, the system prioritizes these IP addresses to keep them unaffected. Private DNS software is also available for independent deployment in office networks, IDCs, or public cloud environments to serve as a recursive or authoritative DNS resolver. For inquiries, contact us on DingTalk: behladu.