Posts from ‘CCDE’
Understanding Third-Party Next-Hop
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 update carries explicit next-hop value, which is used by receiving side, as opposed to the “implicit” next-hop calculated as the sending router’s address – the source address in the IP header carrying the routing update. Such “explicit” next-hop is called “third-party” next-hop IP address, allowing for pointing to a different next-hop, other than advertising router. Intitively, this is only possible if the advertising and receiving router are on a shared segment, but the “shared segment” concept could be generalized and abstracted. Every popular distance-vector protocols support third party next-hop – RIPv2, EIGRP, OSPF and BGP all carry explicit next-hop value. Look at the figure below – it illustrates the situation where two different distance-vector protocols are running on the shared segment, but none of them runs on all routers attached to the segment. The protocols “overlap” at a “pivotal” router and redistribution is used to provide inter-protocol route exchange.
Tags: bgp, CCDE, ccie, eigrp, ospf, rip, third-party next-hop
Abstract
In this blog post we are going to review a number of MPLS scaling techniques. Theoretically, the main factors that limit MPLS network growth are:
- IGP Scaling. Route Summarization, which is the core procedure for scaling of all commonly used IGPs does not work well with MPLS LSPs. We’ll discuss the reasons for this and see what solutions are available to deploy MPLS in presence of IGP route summarization.
- Forwarding State growth. Deploying MPLE TE may be challenging in large network as number of tunnels grow like O(N^2) where N is the number of TE endpoints (typically the number of PE routers). While most of the networks are not even near the breaking point, we are still going to review techniques that allow MPLS-TE to scale to very large networks (10th of thousands routers).
- Management Overhead. MPLS requires additional control plane components and therefore is more difficult to manage compared to classic IP networks. This becomes more complicated with the network growth.
The blog post summarizes some recently developed approaches that address the first two of the above mentioned issues. Before we begin, I would like to thank Daniel Ginsburg for introducing me to this topic back in 2007.
Tags: CCDE, ccie, hierarchical bgp, hierarchical lsp, MPLS, mpls-te, rsvp-te
Are you wondering what the month of August 2010 will bring for INE fans?
Try all new, online bootcamps in the following disciplines:
- MPLS
- BGP
- CCNA
- CCNP
- CCDA
Watch the blog and your email for all of the exciting new details.
Join the INE Experts Online in August
This goal of this post is breif discussion of main factors controlling fast convergence in OSPF-based networks. Network convergence is a term that is sometimes used under various interpretations. Before we discuss the optimization procedures for OSPF, we define network convergence as the process of synchronizing network forwarding tables after a topology change. Network is said to be converged when none of forwarding tables are changing for “some reasonable” amount of time. This “some” amount of time could be defined as some interval, based on the expected maximum time to stabilize after a single topology change. Network convergence based on native IGP mechanisms is also known as network restoration, since it heals the lost connections. Network mechanisms for traffic protection such as ECMP, MPLS FRR or IP FRR offering different approach to failure handling are outside the scope of this article. We are further taking multicast routing fast recovery out of the scope as well, even though this process is tied to IGP re-convergence.
It is interesting to notice that IGP-based “restoration” techniques have one (more or less) important problem. During the time of re-convergence, temporary micro-loops may exist in the topology due to inconsistency of FIB (forwarding) tables of different routers. This behavior is fundamental to link-state algorithms, as routers closer to failure tend to update their forwarding database before the other routers. The only popular routing protocol that lacks this property is EIGRP, which is loop-free at any moment during re-convergence, thanks to the explicit termination of the diffusing computations. For the link state-protocols, there are some enhancements to the FIB update procedures that allow avoiding such micro-loops with link-state routing, described in the document [ORDERED-FIB].
Even though we are mainly concerned with OSPF, ISIS will be mentioned in the discussion as well. It should be noted that compared to IS-IS, OSPF provides less “knobs” for convergence optimization. The main reason is probably the fact that ISIS is being developed and supported by a separate team of developers, more geared towards the ISPs where fast convergence is a critical competitive factor. The common optimization principles, however, are the same for both protocols, and during the conversation will point out at the features that OSPF lacks while IS-IS has for tuning. Finally, we start our discussion with a formula, which is further explained in the text:
Convergence = Failure_Detection_Time + Event_Propagation_Time + SPF_Run_Time + RIB_FIB_Update_Time
The formula reflects the fact that convergence time for a link-state protocol is sum of the following components:
- Time to detect the network failure, e.g. interface down condition.
- Time to propagate the event, i.e. flood the LSA across the topology.
- Time to perform SPF calculations on all routers upon reception of the new information.
- Time to update the forwarding tables for all routers in the area.
Tags: CCDE, ccie, fast convergence, ospf, sub-second convergence, timer tuning
As my 4-year recertification timeline was about to lapse, I had to go and pay $350 to recertify 
There was no other challenge, as I picked CCDE written for recertification, keeping in mind to take the practical test again this year. To my greatest surprise, the exam was almost the same it was in September 2007, when I took the beta version. Just this time the number of questions was 100 not 170 and they give you chance to review and navigate among the questions (just like it was in old CCIE Written). Apparently, the CCDE written test engine has never been updated the way that CCIE R&S Written was, with the new scoring model based on 1000 points. Since 2007 I spent considerable amount of time studying (back then I went unprepared, but still passed with 70 point) so the exam went disappointedly easy, as I haven’t seen anything new that I didnt see in 2007. As usual, the main focus is on IP Routing with the addition of Tunneling techniques (MPLS, GRE, IPSec) along with QoS, Network Management and Network Security. You may find the very detailed blueprint here (though formatting is broken in a number of places):
http://www.cisco.com/web/learning/le3/ccde/ccde_exam_information.html
The books I found most helpful to prepare were:
- Definitive MPLS Network Designs
- BGP Design and Implementation
- IS-IS: Deployment in IP Networks
- OSPF: Anatomy of an Internet Routing Protocol
- Optimum Routing Designs (you may mainly concentrate on IGP protocols and refer to the book above for BGP)
- EIGRP for IP: Basic Operation and Configuration
- Cisco IP Routing by Alex Zinin (for you hardcore routing fans)
- OSPF and ISIS: Choosing and IGP for Large Scale Network
- Layer 2 VPN Architectures
- Interconnections, 2nd edition: Bridges, Routers, Switches and Internetworking Protocols. (Just for fun reading and a lot of background information)
Lastly, anyone preparing for the CCDE certification – even though the written test is easy, do not take it lightly as you’ll need all the knowledge during the practical test. There are other challenges in the practical exam, but hopefully the plan I developed to deal with that will work for me – we’ll see 
Tags: CCDE, ccde blueprint, ccde written, recommended reading, vue
It is with great pride that we announce our esteemed colleague and friend, Scott Morris, quad-CCIE, has passed the Cisco Certified Design Expert (CCDE) exam. Scott joins a select few in the world to have passed this daunting certification. It seems like just yesterday (1998), when Scott passed the Cisco Design Specialist certification.
Please help us DoS attack the comments area of this site to help congratulate Scott!
CCDE #20090013
Scott Morris (left) and Keith Barker in a pre-celebration at Ice Lounge (Las Vegas, USA)
The Beta Test is over! Check out W-INE Radio at:
http://radio.ine.com:8000/listen.m3u
The station features Tech Talks and other fun, educational sessions, as well as CD quality tunes to study by!
The Podcast of our Core Knowledge Section Tech Talk is available at:
http://www.ine.com/podcasts/ckp1.mp3
Do you have programming suggestions? Just e-mail wineradio@ine.com
Our blog site continues to skyrocket in viewers and active participants. Thank you so much for supporting this site and reading and commenting on what we have to say. We love to teach and WRITE, and without your support, the blog WRITING part would certainly be wasted. ☺
One of the things I keep noticing about our blog is Cisco questions pretty unrelated to a particular blog in the comments for a certain post. I wanted to take this opportunity to remind all of our readers about a powerful resource on our site for any questions you might have. It is our Online Community at http://ieoc.com.
February 11, 2009: CCDE Practical Exam
Have you passed your CCDE written exam? Individuals that have completed the written portion of the CCDE exam can register immediately to take the practical portion of the exam. The next CCDE practical exam is scheduled for Wednesday, February 11, 2009, in Chicago, Illinois, US and London, UK. The cost of the exam is $1,400USD. Candidates must have passed the CCDE qualification exam prior to registration.
In this post I will try to summarize the things known so far about the CCDE written/practical exams and provide some (hopefully) useful tips and hint. Even though I didn’t receive my exam results yet, I think it’s still a good idea. At least, I’m still the person who “tried” and haven’t “failed” yet (at least unaware of that
The first question that people ask – would getting CCDA and CCDP help in achieving CCDE? That would help, a little. Most useful thing would be summarization your knowledge of IP Routing protocols and QoS topics. Plus, you can find some useful things in the new ARCH2 training course. However, I don’t think it is necessary to become a CCDP in order to get enough knowledge for taking CCDE.
Loading ...
