2 posts tagged with "OSPF"

Any time I have to do anything with OSPF I remind myself how it can be so damn awkward about MTU. A little while ago I was busy trying to integrate some Juniper SRX firewalls into a perimeter around some Cisco Nexus 7K and reached a problem that looked like MTU, smelled like MTU, quacked like MTU but we couldn't work out how it was MTU. Here's how it was MTU and what we learned.

More than just an interview question​

Over my years in networking I've sat on both sides of countless technical interviews. There's a familiar dance that occurs when discussing OSPF: the candidate confidently states "OSPF uses Dijkstra's algorithm for route calculation," and the interviewer will nod approvingly. Yet recently, I had a moment of clarity: in hundreds of these exchanges, I've never once asked a candidate to explain what that actually means, nor have I been asked to explain it myself. This perfunctory mention of Dijkstra has become almost ceremonial in our industry, a shibboleth that we repeat without truly engaging with its significance. Yet understanding this algorithm isn't just academic—it fundamentally shapes how OSPF operates, influences our network designs, and explains why certain design patterns have become best practices. When a link fails in your network and OSPF begins recalculating routes, there's significant computational overhead that many engineers never consider. This processing cost isn't just theoretical—it's the hidden force behind many of our design decisions, from area sizing to adjacency limits. Today, we'll bridge the gap between theory and practice, exploring how this fundamental algorithm shapes the way we deploy and scale OSPF networks, and why it matters for your day-to-day operations.