What is a ROUTER? // FREE CCNA // EP 2
About this video
In episode 2 of his free CCNA course, NetworkChuck explains what a router does using a Packet Tracer lab. A switch alone lets hosts on the same IP network talk using MAC addresses, but a host that wants a server on a different network cannot reach it directly. He shows, in simulation mode, how a host uses ARP broadcasts to learn MAC addresses: first for a peer on its own network, and then, crucially, for its default gateway (the router) when the destination is off-network. The host sends the frame to the router’s MAC address while keeping the remote server’s IP as the Layer 3 destination; the router then ARPs for the server on the second network, rewrites the Layer 2 addresses, and forwards the packet, with replies returning the same way. He also demonstrates DNS, where a separate DNS server resolves a website name to an IP before the HTTP request follows the same routed path, and shows the router’s routing table with the show ip route command, noting that internet routers hold vastly larger tables learned via protocols such as BGP.
Key takeaways
- A switch connects hosts within one network using Layer 2 MAC addresses; a router connects different IP networks at Layer 3
- Hosts use ARP broadcasts to resolve an IP address to a MAC address, and resolve the default gateway’s MAC when the destination is off-network
- For off-network traffic, the Layer 2 destination is the router while the Layer 3 destination remains the final remote host
- DNS must resolve a website name to an IP address before routing can happen; routers and hosts cache ARP results to avoid repeating the process
- The show ip route command displays the router’s map of networks and interfaces, which on internet routers grows to a very large BGP table
Episode details: published July 26, 2020 · 21:51 long. Summary written by Self Growth Videos from the episode itself. Business results and any income figures mentioned are NetworkChuck’s own claims, shared for education — they are not typical or guaranteed.
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