![]() ![]() When Dyn’s targeted, authoritative DNS servers became unavailable, the attack traveled across the world at TTL speed. As a result, it’s not unusual for ISPs to refresh their DNS cache as often as every 30 seconds. This generally makes them the preferred option. Given the continual increase in internet speeds and the diminishing cost of communications today, short TTL benefits outweigh their disadvantages. A delayed response to any DNS change is one downside, however. Longer cache times equate to fewer lookups, lower costs and better performance. Longer TTLs are mostly appropriate for sites hosted on a single server that don’t frequently change their IP configurations. To manage with this overhead, ISPs set their own rules for minimum allowable DNS refresh rates. The downside of short TTLs is that they result in frequent lookups, increasing the cost to the recursive server providers. Similarly, when moving a domain to a new server, short TTLs direct users to the new IP as soon as possible. A short TTL helps update the system more quickly, making the load balancer more effective. The rate at which the change is propagated is determined by its TTL setting. Here, as soon as traffic needs to be rerouted to a new server, the IP address is changed on the authoritative DNS. ![]() One of the most common use cases is where domains rely on DNS-based load balancing and failover services. Short TTLs are useful for domains that frequently change their records. So what are the considerations for setting TTLs for a website? To a large extent, it depends on the use case and update frequency. As we’ll see, this setting also had a part to play in the Dyn DDoS assault. This brings us to time to live (TTL), which is the value that determines how often the DNS cache is refreshed. This conserves bandwidth and computing resources while also providing quicker user responses. To speed up response times, recursive servers cache the domain information so they don’t have need to request the same data over and over again. The authoritative DNS server is the primary source of domain information it’s where IP addresses are defined and subsequently updated by a domain owner.Īcting as a middleman, recursive servers periodically fetch domain information from their authoritative brethren and pass it to end users. Such translation occurs every time you type a website name in your browser.ĭNS is a hierarchical system comprised of two server types: one is authoritative, while the other is recursive. ![]() In particular, what are the considerations behind using shorter or longer TTL settings? Understanding Time to Liveĭomain name system (DNS) is a service that translates easy-to-remember domain names (e.g., into numerical IP addresses used by the internet to locate and identify computer services and devices. In answering, let’s take a closer look at the role TTL plays in DNS server management. Specifically, readers want to know which TTL settings work best when an authoritative DNS service is taken down by DDoS offenders. Our recent post about the implications of DNS redundancy during the Dyn DDoS assault generated some interesting questions from readers about time to live (TTL) DNS settings and their impact on website availability in the event of an attack. ![]()
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