Jan
03
Continuing my review of titles from Petr’s excellent CCDE reading list for his upcoming LIVE and ONLINE CCDE Bootcamps, here are further notes to keep in mind regarding EIGRP. About the Protocol The algorithm used for this advanced Distance Vector protocol is the Diffusing Update Algorithm. As we discussed at length in this post, the metric is based upon Bandwidth and Delay values. For updates, EIGRP uses Update and Query packets that are sent to a multicast address. Split horizon and DUAL form... Read More
Dec
30
To start my reading from Petr's excellent CCDE reading list for his upcoming LIVE and ONLINE CCDE Bootcamps, I decided to start with: EIGRP for IP: Basic Operation and Configuration by Russ White and Alvaro Retana I was able to grab an Amazon Kindle version for about $9, and EIGRP has always been one of my favorite protocols. The text dives right in to none other than the composite metric of EIGRP and it brought a smile to my face as I thought about all of the misconceptions I had regarding... Read More
Sep
02
Abstract This publication briefly covers the use of 3rd party next-hops in OSPF, RIP, EIGRP and BGP routing protocols. Common concepts are introduced and protocol-specific implementations are discussed. Basic understanding of the routing protocol function is required before reading this blog post. Overview Third-party next-hop concept appears only to distance vector protocol, or in the parts of the link-state protocols that exhibit distance-vector behavior. The idea is that a distance-vector... Read More
Aug
14
In the first part of this series, we subdivided the processes of EIGRP into four discrete steps, and detailed troubleshooting the first two. This is taken from the 5-Day CCNP bootcamp: Discovery of neighbors Exchange of topology information Best path selection Neighbor and topology table maintenance Let us now discuss path selection and maintenance troubleshooting. We should all remember that we can view the topology table of EIGRP with the command show ip eigrp topology. Here we can see the... Read More
Dec
23
CCNA students can typically rattle off the fact that EIGRP uses Bandwidth and Delay in its composite metric calculation by default. In fact, they tend to know this as well as their own last name. But I often notice they might have some pretty big misconceptions about how this metric is really calculated, and how they can manipulate it. Here are some very important "Core Knowledge" facts that we need to keep in mind about the EIGRP metric: Read More
Nov
20
Every once in a while I come across a tip that is so exciting I want to share it with the world. I was recently going through one of the many posts I read, and saw the answer to a question that I have been wondering about for many years. Awesome job to Steve Shaw who came up with this. Here is the scenario. Read More
Aug
03
EIGRP is based on the concept of diffusing computations. When something changes in network topology, the routers that detect a loss of network prefix will send out EIGRP QUERY messages that propagate in circular waves similar to the ripples on water surface. Every queried router will in turn query its neighbors and so on, until all routers that knew about the prefix affected. After this, the expanding circle will start collapsing back with EIGRP REPLY messages. The maximum radius of that circle... Read More
May
01
The problem of unequal-cost load-balancing Have you ever wondered why among all IGPs only EIGRP supports unequal-cost load balancing (UCLB)? Is there any special reason why only EIGRP supports this feature? Apparently, there is. Let’s start with the basic idea of equal-cost load-balancing (ECLB). This one is simple: if there are multiple paths to the same destination with equal costs, it is reasonable to use them all and share traffic equally among the paths. Alternate paths are guaranteed to... Read More
Aug
02
DMVPN stands for Dynamic Multipoint VPN and it is an effective solution for dynamic secure overlay networks. In short, DMVPN is combination of the following technologies: 1) Multipoint GRE (mGRE) 2) Next-Hop Resolution Protocol (NHRP) 4) Dynamic Routing Protocol (EIGRP, RIP, OSPF, BGP) 3) Dynamic IPsec encryption 5) Cisco Express Forwarding (CEF) Assuming that reader has a general understanding of what DMVPN is and a solid understanding of IPsec/CEF, we are going to describe the role and... Read More
Feb
19
UPDATE: For more information on Redistribution see the video series Understanding Route Redistribution – Excerpts from CCIE R&S ATC Simple Redistribution Step-by-Step We're going to take our basic topology from the previous post Understanding Redistribution Part I , and configure to provide full connectivity between all devices with the most simple configuration. Then we are going to tweak some settings and see how they affect redistribution and optimal routing. This is going to be an... Read More

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