Automation and Programmability
Traditional versus controller-based
Traditional networking configures each device by CLI and runs distributed control planes. Controller-based networking centralises the control plane: Catalyst Center (formerly DNA Center) for campus fabrics, SD-WAN Manager for WAN. Northbound APIs face the application or operator and are typically REST/JSON; southbound APIs face the devices (NETCONF, RESTCONF, CLI, SNMP, OpenFlow). Trap: northbound points toward the application, not toward the hardware.
Data formats and REST APIs
JSON uses key/value pairs in curly braces and arrays in square brackets; XML uses nested tags. Map CRUD to HTTP verbs: POST create, GET read, PUT/PATCH update, DELETE remove. GET is safe and idempotent; POST is neither. Status codes to memorise: 200 OK, 201 created, 400 bad request, 401 unauthorized, 404 not found.
Configuration management and CI/CD
Ansible is agentless over SSH. Puppet and Chef use agents with manifests and cookbooks/recipes respectively. CI/CD pipelines test configuration then deploy it; infrastructure as code keeps configuration versioned like software.
Cloud and virtualization
IaaS: you manage the OS and upward. PaaS: you manage only the application. SaaS: you manage nothing. Type 1 hypervisors run bare metal (ESXi); Type 2 are hosted (VirtualBox). Containers share the host kernel and are lighter than virtual machines.
Rule of thumb
If a question asks which tool needs no software installed on the managed device, answer Ansible. If it asks which API direction a Python script uses to reach a controller, answer northbound.