DNS outage avoidance method for recursive DNS servers
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.
1. A domain name system (DNS) server system comprising:
a local cache storing cached DNS answers from previous DNS queries, each of the cached DNS answers having a time-to-live (TTL) value, cached DNS answers having an expired TTL value are expired DNS answers;
an outage avoidance system comprising:
a query processing module that:
is configured to receive a DNS query from a client;
checks the local cache for a non-expired DNS answer to the DNS query; and upon not finding one,
is configured to pass the DNS query to a remote DNS server system;
is configured to receive an empty answer, an error message, or no response from the remote DNS server system; and
an outage avoidance processing module that is configured to, upon indication that the query processing module received an empty answer, an error message, or no response:
check the local cache for an expired answer to the DNS query; and
return the expired answer to the client.
2. The DNS server system of claim 1 , wherein the outage avoidance processing module modifies a TTL value of the expired answer as part of returning the expired answer to the client.
3. The DNS server system of claim 1 , wherein the outage avoidance processing module ignores the TTL value of the expired answer as part of returning the expired answer to the client.
4. The DNS server system of claim 1 , wherein a proxy DNS server system is configured to mediate communications between the client and the DNS server system.
5. The DNS server system of claim 4 , wherein the DNS server system is part of a cluster of DNS server systems.
6. The DNS server system of claim 5 , wherein the proxy DNS server system comprises:
a local cache; and
an outage avoidance system having:
a query processing module; and
an outage avoidance processing module.
7. The DNS server system of claim 1 , wherein the DNS server system is a recursive DNS server system.
8. The DNS server system of claim 1 , wherein the remote DNS server system comprises one or more authoritative DNS servers.