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.
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.
6PE carries IPv6 prefixes across an untouched IPv4 MPLS core using MP-BGP and labels. This post builds a working deployment on Cisco IOS XE and shows the labels, the IPv4-mapped next hops, and an end-to-end IPv6 traceroute.
BGP multipath is one config line, but the rules for when a second path is accepted are not. Cover eBGP, iBGP, and eiBGP multipath on Cisco IOS XE with lab output, including the next-hop rewrite that can hide a real misconfiguration.
A well-designed BGP community scheme turns per-neighbor route-maps into a scalable signaling system. This guide builds one end to end on IOS XE, proves it with lab output, and includes a working RTBH trigger.
Dampening penalises a prefix for flapping and refuses to use it even after it recovers. Captured live on CML with IOS XE 17.18.2: penalty 2818 from three flaps, the prefix held at *d while an identical prefix from the same neighbor stays best, plus the advertisement-interval gotcha that makes...