DNS name servers

• no server has all name-to-IP address mappings

local name servers:

• each ISP, company has local (default) name server
• host DNS query first goes to local name server

authoritative name server:

• for a host: stores that host’s IP address, name
• can perform name/address translation for that host’s name

Why not centralize DNS?

• single point of failure

• traffic volume

• distant centralized database

• maintenance

doesn’t scale!

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