Arista Extensible Operating System (EOS)
EOS questions reward knowledge of its architecture and operational model. EOS is a single-image, Linux-based network OS with a modular, state-driven design: protocol agents (Sysdb clients) publish state to the System Database (Sysdb), and other processes subscribe to it rather than talking directly to each other. This is why EOS supports features like stateful restart and why show commands reflect a consistent shared state.
Know the CLI modes: enable, configure, and config sub-modes; the difference between running-config and startup-config; and how to persist changes (write memory / copy running-config startup-config). Understand management access: eAPI (JSON-RPC over HTTP/HTTPS) is the programmatic interface, and it is the foundation for automation and CloudVision integration. Know AAA basics (TACACS+/RADIUS), role-based access, and the difference between the management VRF and in-band management.
Traps: (1) Assuming a config change survives reload without being saved to startup-config. (2) Confusing eAPI with SNMP - eAPI is structured JSON-RPC, SNMP is for polling/traps. (3) Forgetting that many show outputs are per-VRF and require specifying the VRF. (4) Misreading interface naming (Ethernet1 vs. Ethernet1/1) across platforms.
Rule of thumb: "state-driven" and "Sysdb" point to EOS architecture; "JSON-RPC on port 443" points to eAPI. Worked example: to verify a change is persistent, run show running-config and compare against show startup-config; if they differ, the change is live but will be lost on reload until saved. For automation, enable eAPI with management api http-commands and authenticate over HTTPS.