QSIC L2 Support Engineering Flashcards

A set of 25 vocabulary flashcards covering Linux diagnostic commands, networking protocols, troubleshooting methodologies, and store system triage from the L2 support engineering lecture transcript.

Structured Troubleshooting Approach

A methodology where an engineer defines symptoms, business impact, scope, and start time, isolates the problem by breaking the system into layers, forms a hypothesis, tests it with the least disruptive test, and documents the result.

systemctl status

A Linux command used to check the current state of a service, indicating whether it is stopped, failed, repeatedly restarting, or misconfigured.

journalctl -u service

A Linux command used to review specific service logs and search for error messages around the time of a failure.

Store Device Offline Troubleshooting

A layered process starting from physical checks (power, cabling, link status) up to IP configuration, default gateway, DNS resolution, firewall requirements, QSIC cloud access, and application logs.

IP Address Connectivity Verification

Testing local routing, external IP reachability, DNS resolution, required ports like TCP 443, NTP time sync, and TLS/HTTPS communication to diagnose why a device with an IP cannot reach the cloud.

DNS Troubleshooting Commands

Commands such as 'cat /etc/resolv.conf', 'nslookup example.com', and 'dig example.com' used to inspect configured DNS servers and test hostname resolution.

DHCP vs. Static IP

DHCP automatically provides network settings (IP address, subnet mask, default gateway, DNS) from a central server, while a Static IP is manually configured on the device.

Default Gateway

The router a device sends network traffic to when the destination is outside its local subnet, checked on Linux using the 'ip route' command.

Firewall Connectivity Testing

Using tools like 'nc -vz hostname 443' or 'curl -v https://cloud.example.com' to verify if communication to a specific endpoint and port is blocked.

TLS (Transport Layer Security)

A protocol providing encryption, authentication, and integrity for network communication, where a client validates a server's digital certificate during a handshake before encrypted communication begins.

NTP (Network Time Protocol)

A protocol used to synchronize a device's system clock with a reliable time source, essential on Linux for TLS certificate validation, log correlation, and monitoring.

timedatectl

A Linux command used to inspect the current system time and Network Time Protocol (NTP) synchronization status.

Linux Log Correlation

Defining an incident time window, searching system and application logs for keywords (error, failed, timeout, exception), examining surrounding lines, and establishing a sequence of events.

Store-Side vs. Cloud-Side Failure

A distinction made by evaluating scope: an issue affecting a single store suggests local hardware, network, or configuration problems, whereas a simultaneous multi-store issue suggests a platform or cloud-side problem.

L2 to L3 Escalation Criteria

Escalating a ticket when an issue requires engineering-level intervention (such as product defects or code changes), breaches SLA/impact limits, or persists after systematic L2 testing has ruled out local factors.

Escalation Package Requirements

A handoff structured with issue description, business impact, scope, timeline, tests performed, test results, ruled-out causes, relevant logs/errors, recent changes, current hypothesis, and reason for escalation.

Ticket Prioritization Criteria

Ordering support cases based on business impact, severity, SLA commitments, the total number of affected stores, and whether the issue blocks critical events like a new-store go-live.

Hypothesis Testing Mentality

Treating a proposed explanation as an idea to test against evidence (such as CPU, memory, and logs) rather than an assumption to prove, and quickly abandoning it if data disproves it.

Proactive Grafana Monitoring

Using Grafana dashboards to establish system baselines, observe processing throughput and application backlog, and spot early warning trends before they cause client-facing failures.

Operational Scripting Scope

Using Bash or Python to combine Linux utilities, automate repetitive diagnostic checks, gather system statistics, and process log files to speed up troubleshooting.

RMA (Return Merchandise Authorization) Checklist

Validating power, physical connections, boot process, hardware logs, network config, re-provisioning attempts, and external environmental factors before recommending hardware replacement.

New Store Rollout Investigation Sequence

A step-by-step diagnostic order starting from Power → Cabling/Link → IP Address → Gateway → Internet → DNS → Firewall → NTP → TLS → QSIC Cloud → Application → Provisioning → Stream Validation.

Audio Signal Path Troubleshooting

Tracing an audio issue along the complete hardware and signal route: Cloud Stream → QSIC Device → Audio Output → Audio Cable → Amplifier / DSP → Speaker Wiring → Speakers.

nc -vz

A Netcat command option used to perform verbose connectivity checks on a specific target host and port without sending data.

ss -tulpn

A Linux socket statistics command used to list listening TCP and UDP sockets along with associated process details.