Sometimes, we might want a router interface to participate in an EIGRP routing process (in order to advertise that interface's network) without that interface sending out EIGRP Hello messages. That's what we'll cover in this blog post.
By the way, this is the fourth posting in a series on Understanding EIGRP. If you missed any of the earlier postings, you can check them out here:
Previously, we talked about the network net-id wildcard-mask command issued in EIGRP router configuration mode. This command causes two primary actions:
In our Cisco routing and switching studies, we commonly study routing protocols such as RIP, OSPF, EIGRP, and BGP. However, there's a very scalable, fast converging, link-state routing protocol that often gets overlooked and forgotten. It's Intermediate System to Intermediate System (or IS-IS for short).
IS-IS is primarily found in service provider environments, but even if you're not in the service provider world, you still might run into it at some point during your career. So, I wanted to create a video to take away the fear, uncertainty, and doubt from IS-IS. In this video, we'll look at the basic theory surrounding IS-IS and then go through a simple configuration.
Enjoy the video!
Kevin Wallace, CCIEx2 (R/S and Collaboration) #7945
Once of EIGRP’s claims to fame is its fast convergence in the event of a link failure. However, one thing that might slow down this convergence is timer configuration. That's the focus of this blog post, which is the third in a series of posts on Understanding EIGRP. If you missed the first couple of posts, you can get them here:
Let's beging our discussion of EIGRP timers by considering a situation where two EIGRP neighbors are directly connected to one another. If the physical link between them fails, each router’s connected interface goes down, and EIGRP can fail over to a backup path (that is, a feasible successor route). Such a situation is shown in the following figure:
Routers R1 and R2, shown in the above figure, are directly attached to one another. Therefore, if the cable between them physically breaks, each of the router interfaces connecting to that link go down, and EIGRP realizes that it...
One of the big buzzwords you hear surrounding tech startups is pivot, which is what happens when a company is moving in one direction and makes a strategic decision to go in another direction. For example, the company we now know as Twitter was once known as Odeo, which was going to offer a way for people to subscribe to podcasts. However, with iTunes becoming a dominate force in podcast subscriptions, the decision was made to pivot to a micro-blogging platform.
Sometimes, we need to make a pivot in our own careers based on what we anticipate happening to the industry. For example, many local bookstores have disappeared because of Amazon.com. Blockbuster went bankrupt in their video rental business with the advent of NetFlix and streaming video services.
“The electric light did not come from the continuous improvement of candles.” –Oren Harari
Let’s now consider the networking industry. Personally, I’ve been working with Cisco routers since 1989...
In the first blog post in our Understanding EIGRP series, we were introduced to EIGRP’s features, in addition to a basic configuration example, and a collection of verification commands. Now, in this post, we’ll delve into the behind the scenes action of how EIGRP establishes a neighborship, learns a route to a network, determines what it considers to be the best route to that network, and attempts to inject that route into a router’s IP routing table.
EIGRP’s operations can be conceptually simplified into three basic steps:
Step 1. Neighbor Discovery: Through the exchange of Hello messages, EIGRP-speaking routers discover one another, compare parameters (for example, autonomous system numbers, K-values, and network addresses), and determine if they should form a neighborship.
Step 2. Topology Exchange: If neighboring EIGRP routers decide to form a neighborship, they exchange their full topology tables with each other. However, after the...
I used to work as a Network Design Specialist at Walt Disney World, in Florida. Their massive network contained over 500 Cisco routers (and thousands of Cisco Catalyst switches). What was the routing protocol keeping all of these routers in agreement about available routes? It was Enhanced Interior Gateway Routing Protocol (EIGRP). That’s the focus of this blog post, which is the first of a series of posts focusing on EIGRP.
If you already have your CCNA R/S certification (or higher), you’re probably well acquainted with EIGRP. However, unless you have an eidetic memory (like Sheldon Cooper on The Big Bang Theory TV show), you probably don’t remember every single EIGRP command and concept. Therefore, this series of blog posts is going to review and reinforce those fundamental EIGRP concepts, and even introduce a few other fun facts.
There’s a long-running debate about the fundamental nature of EIGRP. At its essence, is EIGRP a link...
If you’re studying for a Cisco certification, you might be debating what to do for your hands-on practice. Will you buy a home lab? What about using a simulator or an emulator?
Well, before spending any money, consider Cisco’s DevNet Sandbox. For example, let’s say you’re studying Collaboration technologies. You can (for FREE) access a Cisco Unified Communications Manager (CUCM) cluster (in your choice of CUCM version). You can even (virtually) get your hands on an IM and Presence server.
When I first discovered this, I actually felt guilty using it. After all, this resource is at Cisco’s DevNet site, and I’m not a developer. Fortunately, I was talking with one of Cisco’s DevNet folks at Cisco Live this year, and they told me it was not limited to developers. In fact, they encouraged me to let certification students know about this resource, and I’ve got to say it’s remarkable.
Please check out this new video I created to show...
You want to get your first (or next) Cisco certification, but do you have a specific preparation strategy, or are you just winging it? If you do have a structured framework you’re confidently executing against, congratulations! If not, allow me to share my seven-step framework for Cisco exam preparation.
When it comes to learning what you need to learn, the good news is, you’ve got options. Let’s compare a few:
The traditional approach, and the way I trained certification candidates for nearly fourteen years, is to take an official Cisco course from a Cisco Learning Partner (CLP). You might have the option of taking your course at a training facility or on-line, and you typically get access to the gear you need to perform lab tasks during the course. You also get Cisco’s official course material. However, a gotcha that many people don’t realize is that Cisco typically has different groups...
Yet another new topic on the new CCNA R/S v3 exam is BPDUGuard, which is an enhancement to Spanning Tree Protocol (STP) available on our Cisco Catalyst switches. Specifically, BPDUGuard can help prevent a Layer 2 topological loop by placing a port configured for PortFast into an Error-Disabled state if that port receives a Bridge Protocol Data Unit (BPDU).
This video demonstrates the operation of BPDUGuard, and then trains you on how to configure this simple yet powerful feature.
Kevin Wallace, CCIEx2 (R/S and Collaboration) #7945
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