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Q&A: What is DNS TTL?

Description

  • What is TTL?
  • How is TTL relevant to Silverline DDoS Protection? 

 

Environment

  • DNS
  • Silverline DDoS Proxy
  • Silverline WAF

 

Answer

Definition

  • TTL = Time To Live.
  • TTL is a setting in the DNS Record for a domain.
  • TTL is the period of time a record should be stored locally on the client computer before an updated entry has to be retrieved directly from the DNS server again
    • TTL is set by an authoritative nameserver
    • TTL is used for caching purposes
      • The longer the TTL value, the longer the information will be cached
      • The longer the TTL value, the less queries a client will make in order to find the domain resolution

How TTL relates to Silverline DDoS Protection

  • When switching your DNS record to point to Silverline, the change does not take effect until the DNS TTL expires.
  • In DDoS situations, DNS changes are sometimes necessary.
    • The shorter the TTL, the quicker changes take effect.
    • Therefore, at the beginning of any DDoS event, the customer should set their DNS TTL as low as possible: 5min if possible, 30min is common.

 

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