network-fundamentals-cloud

# Network Fundamentals for Cloud The cloud's network is physical hardware pretending to be software. Virtual networks, subnets, security groups, and load balancers are abstractions over a datacenter's actual wires and switches — and every abstraction leaks at the operational layer. This skill covers the networking concepts a cloud-systems practitioner needs to design, debug, and reason about cloud network topology, and the places where the underlying physical reality surfaces as a surprise. **Agent affinity:** hamilton-cloud (datacenter network economics), vogels (service-oriented network boundaries), dean (high-performance intra-datacenter networking) **Concept IDs:** cloud-neutron-networking, cloud-security-groups-policies, cloud-multi-service-coordination ## The OSI Layers, Minus the Nonsense Cloud networking mostly lives at four layers: - **L2 (link).** MAC addresses, Ethernet frames, VLAN tags, ARP. The layer virtual switches speak. - **L3 (network).** IP addresses, routing, subnets. Where SDN controllers live. - **L4 (transport).** TCP, UDP, QUIC. Where load balancers often terminate. - **L7 (application).** HTTP, gRPC, database protocols. Where service meshes live. The cloud network is a stack of overlays: your L2 frames are encapsulated in L3 IP packets that traverse the physical network, unwrapped at the other end, and delivered as if they were on the same switch. Understanding that the overlay and underlay are distinct helps when debugging "this ping should w...