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Commonly confused · Networking Fundamentals

DHCP vs DNS: What's the Difference?

DHCP automatically hands out IP addresses and related settings to hosts when they join a network. DNS translates human-readable names like example.com into IP addresses. DHCP gives you an address; DNS helps you find everyone else's.

Dynamic Host Configuration Protocol (DHCP)

Full definition
vs

Domain Name System (DNS)

Full definition
Dynamic Host Configuration ProtocolDomain Name System
JobAssigns IP configurationResolves names to IP addresses (and back)
PortsUDP 67 (server) and 68 (client)UDP 53 for queries; TCP 53 for zone transfers and large responses
ProcessDORA: Discover, Offer, Request, AcknowledgeRecursive and iterative queries to resolvers and authoritative servers
ProvidesIP address, subnet mask, default gateway, DNS server, lease timeA, AAAA, CNAME, MX, PTR and other records
Failure symptom169.254.x.x APIPA address, no connectivityCan ping by IP but not by name
Across subnetsDHCP relay (ip helper-address)Forwarders and conditional forwarders
Remember it

DHCP gives you your address; DNS gives you everyone else's.

Exam tip

Troubleshooting questions are the classic test: an APIPA address points to DHCP, while reaching a site by IP but not by name points to DNS. Also memorize the DORA order and the port numbers.

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