Recursive DNS Outage Avoidance via Cached Answer Return
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Solution Overview
Problem
DNS outages caused by expired TTL values and temporary unavailability of authoritative DNS servers result in prolonged disconnects between clients and websites, especially in high-traffic and dynamic content environments, due to the inability of recursive DNS servers to provide answers during network interruptions or server unresponsiveness.
Innovation Solution
Implementing a DNS server system with a local cache and an outage avoidance module that allows the return of expired answers to clients even after TTL expiration, reducing the need for recursive DNS servers to query unresponsive remote servers and minimizing downtime by using a proxy DNS server system to manage queries and cache responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the recursive DNS server strictly follows TTL expiration and queries authoritative DNS servers for updated answers, then the DNS answer freshness is improved, but the client disconnection duration increases during network interruptions or server unresponsiveness
Solution Approach 1:
The patent applies preliminary action by having the recursive DNS server proactively detect when an authoritative DNS server is unresponsive (network interruption or error state) and immediately switch to returning a previously cached answer to the client, rather than waiting for the TTL to expire. This preemptive switch prevents the client disconnection that would otherwise occur during the TTL period, while still maintaining answer freshness by only using the cached answer when the authoritative server is temporarily unavailable.
2Measurement precision
If the recursive DNS server queries the authoritative DNS server frequently to ensure answer freshness, then the DNS answer accuracy is improved, but the load on the authoritative DNS server increases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the behavior of the recursive DNS server based on the responsiveness of the authoritative DNS server. When the authoritative server is unresponsive (indicated by network interruption or error), the recursive server changes its parameter from strictly requiring fresh answers to accepting previously cached answers, even if their TTL has expired. This conditional parameter change reduces the frequency of queries to the authoritative server while maintaining answer accuracy when possible.
3Reliability
If the recursive DNS server returns an error when the authoritative DNS server is unresponsive, then the DNS answer reliability is improved, but the service availability to clients deteriorates
Solution Approach 1:
The patent applies dynamics by making the recursive DNS server's response behavior adaptive rather than static. Instead of always returning an error when the authoritative server is unresponsive, the server dynamically adjusts its behavior: it returns a cached answer when the authoritative server is temporarily unavailable, and only returns an error when the cached answer is genuinely invalid or when multiple refresh attempts fail. This dynamic adaptation maintains service availability while preserving answer reliability through conditional logic.
Data Source
AI summary
This disclosure describes systems, methods, and apparatus to protect users of the Internet from DNS outages. In particular, an outage avoidance system is provided that includes query processing, outage avoidance processing, and a local cache, all configured to extend the TTL of expired answers to DNS queries or to ignore the expiration of an answer's TTL value, and thereby provide the expired answer in response to a client request when a DNS server is unable to obtain an answer from a remote DNS server.