Stage 1 · Lesson 8 of 8

DHCP and DNS

Two services make networks usable. gives a device its address, mask, and DNS servers automatically, in four messages: Discover, Offer, Request, Acknowledge. Because Discover is a , a must relay it to a DHCP server on another subnet, which on Cisco is the ip helper-address command.

DNS turns names into addresses. An maps a name to IPv4, AAAA to IPv6, CNAME to another name, MX to a mail server and PTR back from an address to a name. Learn nslookup and dig, because many "the network is down" tickets turn out to be DNS.

Common traptesting a DNS change immediately and assuming it failed, when the old answer is still cached until its TTL (time to live) runs out.

A question to check yourself, an AI practice session and 2 cheat sheet entries come with the full roadmap. Unlock

Resources for this stage

Start with· follow one of these

PlatformFree
Cisco Networking Academy
Cisco · Beginner
Start with the free, self-paced Networking Basics course; it uses Packet Tracer from the first modules
VideoFree
Computer Networking: A Top-Down Approach (Video Lectures)
Jim Kurose and Keith Ross · Intermediate
Free university-level lectures from the authors of the classic textbook, for the why behind every layer

Practise

Cisco Packet Tracer
Build a two-subnet network and use simulation mode to watch ARP, DHCP and pings step by step

Keep handy

Wireshark User's Guide
Capture your own traffic and read real headers; the display filter chapter is the one to bookmark

Also worth your time

TCP vs UDP: The Key Differences Every Developer Should Know (opens in a new tab)Read
A clear comparison of the two transport protocols and when each one fits
Beej's Guide to Network ProgrammingGo deeper
If you code, write a tiny TCP and UDP client and server to see the transport layer from the inside