STP Root Port Election Worked Example: Cost, Neighbor BID, and Port ID
Calculate root ports on six switches using cost, neighbor BID, and sender port ID. Check real outputs, then change one cost to move SW4’s root port.
Labs
Hands-on Cisco IOS XE lab walkthroughs. Each lab ships with a real CML topology, configs you can paste, and verified show output. Articles tagged Labs cover the full CCNA 200-301 blueprint across Network Fundamentals, Network Access, IP Connectivity, IP Services, and Security Fundamentals.
Latest posts — page 2
Cisco Port Security vs MAC Flooding: Limit Learning, Fix Shutdowns
Test Cisco port security against MAC flooding: 17,991 learned entries, a three-MAC protected table, and a phone-plus-PC shutdown fixed with maximum 2.
Cisco IPsec Phase 1 Up, Phase 2 Down: Five IOL Lab Tests
Phase 1 up, Phase 2 down on Cisco? Diagnose four IOL VPN outages with real debug, NAT and ESP evidence, plus a lifetime mismatch that kept working.
802.1X Dynamic VLAN Assignment Not Working: FreeRADIUS Lab
Trace a FreeRADIUS VLAN typo from Access-Accept to an unauthorized Cisco port. Compare sessions, syslog, pings, and Zeek, then verify the fix.
802.1X Shared Secret Mismatch: A FreeRADIUS Lab
Reproduce one switch-side RADIUS key mismatch on IOSv-L2. Compare formal authorization, FreeRADIUS drops and captures on both links, then restore the key and verify EAP-TLS and bidirectional traffic.
ASA NAT Troubleshooting: Stale Manual NAT Overrides Static NAT
Fix an ASA static NAT publish hijacked by a stale manual rule. Follow packet-tracer, NAT hits, syslog 106023, and Zeek S0-to-SF recovery in this lab.
Running the Cisco Catalyst 9800-CL in Containerlab
A custom vrnetlab build for the Cisco 9800-CL, the console and management fixes it needed, and the checks that proved SSH and the web GUI worked.
Cisco Trunk Up, Linux Ping Fails: Find the VLAN Mismatch
Build a working Linux-to-Cisco VLAN link, move the host to the wrong VLAN, and use ARP captures and the MAC table to find and fix the failed ping.
Top Linux Networking Commands: The 2026 Field Reference
Every Linux networking command that matters, grouped by the question it answers, with real captures from a four-hop lab and the triage order to run them in.
ufw: Simple Firewalling on Debian and Ubuntu
Enable ufw without losing your SSH session, learn the rule grammar, and see exactly which iptables chains it builds underneath.
nftables: The Modern Linux Firewall
Your iptables rules already run on nftables. Handles, named sets, inet tables and atomic ruleset loads, all proven with real output from a live lab.
iptables Fundamentals: Tables, Chains, Real Rules
Tables, chains and rule order, demonstrated with real captures from a Debian host in a live lab: DROP against REJECT timing, conntrack, logging and NAT.