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Hectal
Phase 4Intermediate5 of 8 in Networking

Routing, NAT & the Edge

How packets find their way: ARP and switching, routing tables and default gateways, NAT and PAT, BGP and anycast on the internet, and CDNs at the edge.

Phase 1 gave every host an address; this phase moves packets between them. You'll see the same ideas at three scales: inside one Linux host (its routing table), inside a VPC (route tables and NAT gateways from the AWS course), and across the internet (BGP and anycast).

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4 topics ~28 min 7 code blocks & diagrams
Start with the first topic
1
4.1

Local Delivery: MAC Addresses, ARP & Switches

Inside one local network, frames are delivered by MAC address; ARP maps a neighbour's IP to its MAC, and switches learn which port each MAC lives on.

7 min 1 code practice

2
4.2

Routing Tables & Default Gateways

Every host and router has a routing table; for each packet it picks the most specific matching route (longest prefix), falling back to the default route.

7 min 1 diagram 1 code practice

3
4.3

NAT & PAT: Sharing Addresses

NAT rewrites addresses as packets cross a boundary; PAT (port address translation) lets thousands of private hosts share one public IP by also rewriting ports, tracking each connection in a table.

7 min 1 diagram 1 code practice

4
4.4

BGP, Anycast & CDNs

BGP is how independent networks tell each other which address ranges they can reach; anycast announces the same addresses from many places so users reach the nearest; CDNs use both to serve content close to users.

7 min 1 diagram 1 code practice