Open Shortest Path First, the link-state IGP behind most enterprise networks. Articles tagged OSPF cover neighbor relationships, LSA types, areas, DR/BDR election, and Cisco IOS XE configuration.
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.
A complete dual-stack OSPFv3 configuration on Cisco IOS XE, from ipv6 unicast-routing to verified end-to-end reachability, with every capture taken from a live CML lab.
OSPFv3 is a protocol redesign, not OSPF with longer addresses, and with address families it carries IPv4 too. See what changed from OSPFv2, what stayed identical, and what it looks like on the wire in a live Cisco IOS XE lab.
Two border routers redistributing between the same domains give every prefix a feedback path. Build the forwarding loop live on Cisco IOS XE, capture it happening, then fix it with route tags the way production networks do.
Route redistribution end to end on Cisco IOS XE: how seed metrics work, what each protocol demands before accepting foreign routes, and what the routing table looks like at every stage. Every capture comes from a live CML lab.
Before LSA types make sense, you need what an LSA actually is: one record in the link-state database describing one piece of the network. This post covers the LSA as a building block and how it gets everywhere it needs to be.
OSPF passive-interface stops Hellos and adjacencies on an interface but still advertises its subnet. Config, the default pattern, and the route-filter gotcha.
When OSPF and BGP both know about the same prefix, who wins? A practical walkthrough of mutual redistribution, the admin-distance trap, and why BGP into OSPF needs a filter or it takes down your domain.