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OSPF

OSPF is like a traffic director for the internet. Imagine a city with many roads - OSPF helps routers (the traffic directors) figure out the best paths for data to travel from one place to another. It’s like a smart GPS for computers, making sure information takes the shortest and fastest routes. OSPF routers talk to each other, share maps of the internet, and decide the best ways to send data. It’s a cool system that keeps the internet running smoothly!

ChatGPT explaining OSPF to a high-school kid

Configuration Tips

This blog started as a collection of (hopefully) helpful configuration tricks, and I documented numerous Cisco IOS configuration tips in the early 2000s.

Implementation Details

Let’s start with the elephant in the room: OSPF areas – a simple concept that got way too convoluted when OSPF started accreting nerd knobs like NSSA areas:

OSPF default routes are another confusing topic. You could have inter-area default routes (used in stub areas) or external default routes that could be conditional or unconditional.

OSPF adjacencies are another fun troubleshooting topic:

The inimitable forwarding address in type-5 LSA will make your head explode when combined with the NSSA areas.

Want even more OSPF details? I documented way too many of them since I started blogging, including:

Deploying OSPF

Creative networking engineers often forget an unpleasant truth: OSPF is a single security domain. You should never run it with less-trusted peers, be it your customers, data center servers, or virtual machines.

OSPF by itself is complex enough, but the real fun starts when you combine it with other protocols (for example, BGP and LDP):

Running OSPF in large hub-and-spoke networks (for example, large DMVPN networks) is another tough challenge:

While you could use OSPF to get unequal-cost multipathing, you might be tripped by numerous caveats; no wonder there are few implementations of this concept.

Finally, you can run OSPF over unnumbered interfaces, be it point-to-point serial links or Ethernet segments:

Rants

Now and then, I couldn’t resist writing an OSPF-related rant:

What Others Are Writing About OSPF

Other OSPF Blog Posts

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EVPN

EVPN, or Ethernet Virtual Private Network, is like a smart system that helps computers and devices in a network talk to each other better. It’s like having a super organized mail system where each computer has its own address, and EVPN makes sure messages get to the right place quickly and safely. So, it’s kind of like a traffic manager for information on a computer network, making everything run smoothly and securely.

ChatGPT trying (and failing) to explain EVPN

What Is EVPN?

Before going into the technical details, let’s start with the basics: What is EVPN, how does it work, and where can you use it?

EVPN Designs

EVPN was designed to be used in an IBGP environment on top of an IGP. With the eruption of EBGP as better IGP hype, many vendors tried to adapt EVPN to an environment running EBGP instead of OSPF. We covered some of the typical EVPN designs in these blog posts:

Other blog posts focus on various design details:

Finally, several blog posts describe various EVPN VPN topologies:

EVPN Implementation Details

There are tons of tiny little things that can go wrong when you try to deploy EVPN. I documented them as I stumbled upon them:

Beyond VXLAN

While EVPN is often used with VXLAN today, it was designed to work with the MPLS data plane, resulting in a few quirks:

EVPN Rants

Some vendors’ marketing engineers (or Senior Directors) can’t stand anyone telling them their implementation might be suboptimal, going to great lengths to prove to themselves they’re right, and generating beautiful fodder for rants.

Videos

You can watch numerous videos from the EVPN Technical Deep Dive webinar without an ipSpace.net account:

What Others Wrote About EVPN

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