Ask why a campus network has an "access layer" or why data centers abandoned the tree design entirely, and you're asking about topology architectures - CCNA exam objective 1.2 and, more usefully, the vocabulary every design
"The network is slow" tickets that turn out to be a duplex mismatch are a rite of passage. The link is up, pings work, and yet throughput is terrible and retransmissions are everywhere. This article shows you how
Every frame a switch forwards is a lookup in one table: the MAC address table (historically the CAM table). Understanding how entries get into that table, how long they stay, and what happens when a destination isn't in
Subnetting is the one CCNA skill you cannot fake. Every other topic gives you partial credit for concepts; subnetting questions have exactly one right answer, and the exam expects you to find it in under a minute. The good news:
EIGRP does not have one administrative distance, it has three. That surprises people who memorized "EIGRP is 90" for an exam, then watched a redistributed route show up as 170 or a summary route as 5. The three
We broke a healthy lab path three ways on real Cisco routers. Learn the three fingerprints of slow throughput and the iPerf3 tests that expose each.
Foreground vs daemon mode, the one-test-at-a-time busy error, multi-port servers, systemd units, and the firewall rules an iPerf3 test server actually needs.
Two tools, not two versions: they do not interoperate, flags collide, and each wins different jobs. Real output from iperf 2.2.1 and 3.18 shows exactly where they differ.
Why fast links benchmark slow: bandwidth-delay product, a real 78% throughput collapse from a 64K window at 104 ms RTT, and how parallel streams buy it back.
UDP mode measures what TCP hides: loss, jitter, and reordering. Real lab captures show a clean test, a 29% loss over-drive, and how to find the loss knee on any path.
Learn iPerf3 from install to JSON automation, with every output block captured live from a routed Cisco lab - including how to actually read Retr, Cwnd, and sender vs receiver lines.
The technical and behavioral questions network engineer interviews actually ask, with strong answers, 2026 salary bands, career paths after CCNA, and resume keywords that pass the ATS.