Stage 1 · Lesson 7 of 8
ARP and the default gateway
A host sends frames to , not , so it needs a way to find the MAC for an IP. (address resolution protocol) "who has 10.1.20.1?" and the owner replies with its MAC, which is then cached. If the destination is on another subnet, the host does not ARP for it at all.
It sends the frame to its , the router for its subnet, and the router takes it from there. Following one packet from a PC to a server in another network, noting every ARP, MAC and IP along the way, is the best exercise in this stage.
Common trapthinking the destination MAC in a frame is the far server's: across a router, it is always the next hop's MAC.
A question to check yourself, an AI practice session and 1 cheat sheet entry come with the full roadmap. Unlock
Resources for this stage
Start with· follow one of these
- PlatformFreeCisco Networking Academy
Cisco · Beginner
Start with the free, self-paced Networking Basics course; it uses Packet Tracer from the first modules
- VideoFreeComputer 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
Keep handy
Also worth your time
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