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.
Tunnels up, neighbors up, routes missing: split horizon breaks EIGRP over DMVPN's mGRE cloud. Covers split horizon and next-hop-self, dual-hub design, and the dual-homed loop, with real CML output.
Offset lists add metric to specific routes on a specific interface in a specific direction, without touching delay for everyone else. See them steer spokes to HUB1 in a dual-hub DMVPN on IOS XE, with exact before and after metrics.
EIGRP summarization shrinks routing tables but hides detail. A leak map lets you advertise the summary and still punch through specific prefixes that must stay visible. Shown working on Cisco IOS XE with real DMVPN lab output.
EIGRP Site of Origin stamps routes with an extended community so dual-homed WAN sites do not learn their own prefixes back. Covers what SoO does, how it is configured, and what we actually found trying it on IOS XE.
Five OSPF faults built and broken for real in a CML lab, ticket style: the symptom, the two commands to compare, the actual output, and the fix for each one. OSPF rarely tells you what is wrong; this method finds it anyway.
OSPF compares route types before metrics, so a worse metric routinely wins. Prove the full O, O IA, E1, N1, E2, N2 ordering by injecting the same prefix six different ways into a live CML topology and watching each one take over.
area range, filter-list, distribute-list, summary-address: four OSPF filters that are not interchangeable. Side-by-side lab output shows which ones change the LSDB and which only touch the local RIB.
The OSPF forwarding address can point a Type 5 route at a next hop that never advertised it, or silently drop it from the RIB while the LSA sits in the database. This article covers the five conditions that set it and the failure it causes.
max-metric router-lsa tells OSPF a router is still here but a terrible choice for transit, so traffic drains before you reload it. Covers the RFC 6987 stub router advertisement, its options, and a lab demonstration.
Transit /30s and /31s fill OSPF routing tables with prefixes nobody sends traffic to. Prefix suppression removes them with one command. See it working on Cisco IOS XE, plus the consequence that bites during troubleshooting.
SPF and LSA throttle timers control what OSPF does after a failure is detected. Learn the exponential backoff algorithm, the modern IOS XE defaults, and how to tune convergence without letting a flapping link spike every CPU in the area.
Five broken BGP scenarios built and broken for real in a CML lab, each worked ticket style with the actual diagnostic output and the actual fix. The method: every BGP problem is one of four things, checked in order.