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.
INIT means "I hear you, you do not hear me". One router shows a neighbor in INIT, the other shows an empty table, and that asymmetry is the entire diagnosis. Captured live on IOS XE 17.18.2 in CML with an inbound ACL eating OSPF in one direction.
OSPF is the dynamic routing protocol you are most likely to meet on a Cisco ASA. When a firewall needs to learn more than a handful of internal prefixes and the core already speaks OSPF, running it on the ASA
Sooner or later somebody decides the network is moving from EIGRP to OSPF. Maybe a merger brought in a multi-vendor estate. Maybe the standards team decided on open protocols. Maybe an architect just likes link-state better. The reason
Redistribution between two routing protocols at a single point is easy. Redistribution between two routing protocols at two points is where networks go to die, and it is the reason redistribution has such a fearsome reputation in the CCIE lab.
OSPF has an unhelpful habit: when you break it, it usually says nothing. An adjacency that should form simply does not. A route that should be in the table simply is not. There is one failure mode - exactly one - where
Two routes to the same prefix. One has a metric of 20. The other has a metric of 31. Which one does OSPF install? If you answered "the one with metric 20", you have just failed a very
OSPF gives you four different ways to stop a prefix from getting somewhere, and they are not interchangeable. Two of them remove the LSA from the link-state database. One leaves the LSA in place and only touches the local
Here is a routing puzzle. An OSPF router has a route to an external network. The route is in the routing table. The next hop is a device that is not the router that advertised it and is not even
You need to reload a core router. It is carrying live traffic. The naive approach - just reload it - drops every packet in flight and triggers a reconvergence storm. The slightly-less-naive approach - shut its interfaces one at a time
Look at your routing table and count how many of those prefixes anyone actually sends traffic to. In a typical service provider or large enterprise core, a large fraction of the OSPF routing table is transit link subnets - the /30s
OSPF converges fast. That is its whole reason for existing. But "fast" is a tuning decision, and the knobs are not where most people look. They are not the hello and dead timers - those control failure detection. The
This is the hands-on half of our OSPFv3 coverage: a complete dual-stack configuration on Cisco IOS XE, from ipv6 unicast-routing to verified end-to-end reachability, with every capture from a live CML lab. If you want