CCIE-level material for engineers past the CCNP line. Articles tagged CCIE cover expert-track routing, overlays, security and automation, with full configs and real device output from CML.
A dual-hub DMVPN can black-hole spoke-to-spoke traffic for two hours after a hub fails because of one default timer. This post builds the design in CML, fails a hub, and shows exactly what breaks and how to fix it.
When two customer sites share an AS number, BGP loop prevention breaks their MPLS L3VPN on purpose. Reproduce the failure in a CML lab and fix it three ways: as-override, allowas-in, and SoO, with real output for each.
6VPE carries IPv6 L3VPN across an IPv4 MPLS core using the same VRFs, RTs, and MP-BGP sessions you already run. This article builds it in CML and shows the two-label stack that makes it work.
Five Layer 2 faults built and broken in a CML lab, ticket style: VLANs, trunks, and a spanning tree quietly blocking the port you need. Real show output, real syslog messages, and the real fix for each one.
SDM templates, errdisable recovery, and CAM aging: the unglamorous switch administration features that prevent table-full errors, dead ports, and mystery flooding, with real output from a CML lab.
ARP believes any answer it hears, which is why ARP spoofing works. Dynamic ARP Inspection and IP Source Guard fix that using the DHCP snooping binding table. Real CML output, plus an honest note on what a virtual switch can enforce.
DHCP snooping builds the binding table that DAI and IP Source Guard depend on. You see how the table populates, trusted vs untrusted ports, Option 82, and verification, with real CML output and an honest platform limitation.
One flooding host can saturate an entire VLAN. Storm control caps broadcast, multicast, and unknown-unicast rates per port; this covers the configuration, both threshold styles, the right action, and an honest note on platform support.
A link that transmits but cannot receive never hears the BPDU telling it to block, and spanning tree loops. UDLD detects unidirectional links and shuts the port first. Covers normal and aggressive mode with real CML output.
An MST core touching a Rapid-PVST access layer is one of the most misunderstood seams in Layer 2. Build the boundary in a CML lab, see the CIST at work, and deliberately trigger the PVST simulation inconsistency so you can recognize it.
Migrate a live network from EIGRP to OSPF without dropping a packet: run both protocols side by side, then flip administrative distance one command at a time. The ships in the night technique with real lab output.
Two-point redistribution is where networks go to die. This article builds the classic CCIE failure for real in a CML lab, shows a route being re-injected into the protocol it came from, and then fixes it with the exact output at each step.