Networking Fundamentals

Reading about BGP and configuring BGP are two different things. Theory gives you a mental model. Configuration gives you the humbling experience of staring at a neighbor that won’t come up while everything looks correct. This is the post that gets you from zero to a working eBGP session with proper route filtering. The commands

You’ve been reading about BGP. You understand what it does. You have a rough handle on path selection and the difference between eBGP and iBGP. Now someone in your organization is asking whether your network needs BGP, or maybe you’re the one asking. Let’s settle this properly. The answer is almost always simpler than people

BGP path selection is the thing people memorize for certification exams and then forget the moment the cert is in hand. Don’t do that. BGP best path is the algorithm that actually decides which route your traffic takes. If you don’t understand it, you can’t troubleshoot it. And when something breaks at 2am, you’ll be

Before two routers can run BGP together, they need identities. Not usernames and passwords, though those exist too. What BGP actually cares about is the autonomous system number. That ASN is the foundation of how BGP figures out where routes came from, whether they’re legitimate, and how to prevent loops. If you’ve glossed over ASNs

Everything in networking has a cost. Sometimes it’s bandwidth. Sometimes it’s processing overhead. With iBGP, the cost is session count, and it gets ugly fast. If you’ve spent any time with BGP documentation, you’ve heard the phrase “full mesh.” If you haven’t, you’re about to. And once you understand why it’s required and what it

If there’s one thing that trips up engineers new to BGP, it’s the difference between eBGP and iBGP. Not because the concept is hard, but because the implications are sneaky. The sessions look the same. The commands are almost identical. But the behavior is different enough to absolutely destroy a network if you’re not paying

Someone on your team suggested BGP. Or you read an article. Or you watched a conference talk where the speaker made it sound like BGP was the answer to everything. And now you’re wondering if your network actually needs it. For most networks, the answer is still no That’s not a knock on BGP, it