May
14
Hi Everyone! The Challenge People tend to underestimate the important of IGP routing features in modern network. So here is a small challenge scenario for you to practice OSPF traffic engineering. Take a look at the diagram below for information on the topology and link bandwidth. You may assume that every router has a loopback interface for network testing and OSPF router-id selection. There is a large cloud of media servers behind R4, and the users behind R1 need to use full 300Mbps of... Read More
Jan
01
In this blog post we are going to discuss some OSPF features related to convergence and scalability. Specifically, we are going to discuss Incremental SPF (iSPF), LSA group pacing, and LSA generation/SPF throttling. Before we begin, let's define convergence as the process of restoring the stable view of network after a change, and scalability as the property of the routing protocol to remain stable and well-behaving as the network grows. In general, these two properties are reciprocal, i.e.... Read More
Sep
17
This is the follow up discussion for the post titled, "Have you seen my Router ID?" The underlying issue here was trying to get OSPF to bypass the usual selection process for Router ID. The normal selection order is: Manual router ID configured under ospf process Highest IP address of a loopback in the up state in the respective routing table Highest IP address of an interface of an up state in the respective routing table If there are no up interfaces and you have not manually configured a... Read More
Sep
17
In yesterday's post, titled "Have you seen my Router ID?", a challenge section was provided. This post will focus on scrutinizing the section itself, from a strategy / analysis point of view. From a high level overview, we have two devices peering OSPF over a FastEthernet link, with some loopback networks advertised by one side, and received on the other router.  If that was all that the section was asking for, then it should be a task that anyone at CCNA level could complete.  When looking at... Read More
Sep
16
There is more than one possible solution for this challenge. Feel free to post your proposed answer in the comments section. We will try to keep comments hidden from public view, so that the fun isn't spoiled for others. Also, don't feel bad if the answer(s) aren't immediately apparent. A number of very bright people have been puzzled by this scenario.  Answers will be posted on Friday, September 18th. Read More
Sep
15
The feature we are going to talk about today may look a bit convoluted, but it demonstrates core OSPF behavior: combining link-state and distance-vector behaviors. The command capability transit was introduced in IOS 12.3T and is on by default. However, the description is rather confusing and does not explain the underlying mechanics. We are going to give an in-depth look at this feature now. What is Transit Capability? In short, this is a special property of a non-backbone area that allows... Read More
Aug
17
Intro There was a lot of blogging related to OSPF topics recently. In this post, I would like to clarify some common misunderstandings that many people have about OSPF route filtering. I have seen so many folks wrongfully understanding the underlying behavior so it's about time to make the things clear. Read More
Aug
05
As a former English Major at the University of Massachusetts, Amherst, I really loved the oxymoron. You remember those..."sharply dull" or "cruel kindness". Well, the OSPF protocol has one whopper of an oxymoron in its special areas - The Totally, Not-So-Stubby area! When we last left our Area 11 in Part 4 of this blog series, it was a Not-So-Stubby Area, with the default-information-originate command used on the Area Border Router (ABR) in order to ensure a default route existed in the area.... Read More
Jul
26
Welcome back to our series on OSPF areas. Click here for Part 1 of the series. It is time to focus on normal areas and stub areas in this post. Recall our topology: Read More
Jul
25
Thanks to one of our brilliant CCIE R/S Written students, Nish, for his request of this series of INE blog posts. Nish is still struggling a bit with the different OSPF area types and how exactly they impact Link State Advertisements (LSAs). In this series, we will tackle each of the different OSPF areas in great detail, confirming our Level 1 knowledge at the command line as we progress. Here is the network we will use in this first post. Notice this simple network can be constructed easily in... Read More

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