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I have two WAN from different providers, I would like to know how can I manage an IP failover to switch services in case of failur of the primary WAN. The only solution that I know is to use dns records and switch them in case of failure.

  • Is there any service to switch them automatically?
  • If I set a low TTL for my dns records can I be sure a fast switch from clients all over the world? Do DNS cache servers consider my TTL settings?

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KEMP load balancers are an example of load balancers that monitors the backend servers and updates the DNS A records that it serves. It can do "active/active" load balancing by giving back multiple A records, i.e. round robin load balancing; or it can use "active/passive" load balancing, only giving back the second A record when the first fails.

As for the time-to-live (TTL; not TLS!) of your resource records, most DNS resolvers cach them correctly so a low TTL will allow for a quick failover. It is rumored that there are (were?) ISPs that modify their installation of BIND to artificially increase the TTL of records they cache, but I do not believe that is still the case.

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  • Not providers per se, but in company networks caching results of upstream DNS servers is still a very common practice.
    – pacey
    Dec 13, 2018 at 8:38
  • @Tom sorry for TLS typo, of course it was TTL! I edited my post.
    – Tobia
    Dec 13, 2018 at 9:12
  • @pacey: Caching is not a problem. Caching is good. But they should respect the TTL of the resource records and apparently some ISPs do not (or did not) respect the TTL of e.g. 5 minutes and always set a minimum TTL of e.g. 24 hours.
    – Tommiie
    Dec 13, 2018 at 22:41

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