Nexnet AcademyV1 · alpha
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← CourseDNS, DHCP, NAT, Services~6 min read

The services that make the internet usable

DNS: names to addresses

Humans use names (app.local); packets need IPs. A client asks its configured DNS server to resolve the name. If the IP works but the name doesn't, it's DNS - the server may be unreachable, not running, or missing the record. 'Is it DNS?' is the first question in most outages.

DHCP: automatic addressing

Instead of typing an IP into every device, DHCP hands them out. A client broadcasts a Discover; a DHCP server offers an address, mask, gateway, and DNS from its pool. No server or an exhausted pool means a device comes up with no address at all.

NAT and ports

NAT rewrites a private source address to the router's public one so private hosts can reach the internet (and translates replies back). Ports identify services on a host - HTTP on 80, HTTPS on 443, SSH on 22 - so one server can offer many services at once.

Concept cards

DNS

Resolves domain names to IP addresses via a DNS server's records.

The internet's phone book.

DHCP

Leases IP configuration to clients automatically from a pool.

A host stand seating guests at numbered tables automatically.

NAT

Translates private source addresses to a public one for internet access.

A front desk that swaps your room number for the hotel's public phone number.

Port

A number identifying a specific service on a host (80=HTTP, 443=HTTPS, 22=SSH).

Apartment numbers within one building's address.

Now try it
M6-01IP Works, Name Fails
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