I missed writing , missed writing a post lot on the website specifically !. Because I know you are reading right now and wonder where I have been.

I just checked and seen that my last post was on October 26. More than 2 months , I didn’t share anything on the website. I wanted to come here and share something , technical or social , but believe me guys November and December 2017 was so busy from my side.

One of the activity which took my time during this period was Telecom Operator design training which I did in Kenya/Nairobi on November. Safaricom Kenya – Incumbent Telecom Operator/Internet Service Provider.

It was 5 days training and IP/MPLS Backbone planners , Transport network engineers, mobile access and core engineers , fix and mobile wireless service engineers (They have very good fiber penetration in the country) many people attended this training.

Most of the topics were from my CCDE training blueprint but after couple discussions with their lead engineers, we removed CCDE Practical scenarios and couple other topics , as they won’t attend CCDE exam , but added other technologies which they are considering to implement and some of those technologies is Continue reading

Many of my students have been asking whether CCDE Practical/Lab Exam Result policy is still the same.

As you might know after CCDE 2017 May exam cancellation , practical exam results can be learned after 8 to 12 weeks. This mean, if you attend CCDE Practical exam, you cannot learn the result (Pass or fail) on the same day. It was the case until CCDE 2017 May exam.

You used to finish the 8 hours exam and when you click the end exam button, exam result was just there !

This is not the case anymore. Last CCDE Practical exam was on November 2017 and the attendees are still waiting their results as of today. There is no any new announcement by Cisco and I would expect the same thing for February 27, 2018 CCDE Practical exam.

Learning exam result is good probably for the exam security but I hear complaints from the students and i think some of my readers are thinking the same.

They say, if they knew that they failed , they could schedule the next exam. Exam results of the previous one arrives right before the next one , thus , candidates cannot find a time to Continue reading

GLBP stands for Gateway Load Balancing Protocol. In this article, I will explain where GLBP is used , where it shouldn’t be used with the topologies.

GLBP is a Cisco preparatory protocol. In most networks, design requirements might be to use only standard based protocols. If that is the case, GLBP is not a standard based protocol and business cannot use it.

Unlike HSRP and VRRP, GLBP supports flow based load balancing.

HSRP and VRRP can only supports active/standby redundancy or Vlan based load balancing.

GLBP was invented to provide an active-active traffic forwarding the network traffic but there is almost no use case in today networks.

In some cases, GLBP has create more problem than it should solve.

Figure – GLBP at the Enterprise Internet Edge

In the above picture, I depict classical Enterprise Internet edge network. Firewall, Layer 2 switch and Internet Gateways.

Service Providers don’t use stateful devices such as Firewall at the Internet edge.

If in this network, GLBP is used, firewall would send an ARP for the default gateway and only one of the Internet Gateway routers would be used as a default gateway. If there would be two firewalls, another firewall could Continue reading

What is urban and rural area ? What is underserved area in networking ?

These definitions are heavily used in networking. And all broadband network designers take always these definitions into an account while they do their design. I think knowing these definitions as a network engineer is valuable for you.

In general, a rural area or countryside is a geographic area that is located outside towns and cities

Whatever is not urban is considered rural area though some people uses less populate than urban but more populated than rural area as suburban area

Typical urban areas have a high population and large settlements

Typical rural areas have a low population density and small settlements

Underserved areas where there is no good network coverage (Broadband , Voice or any other data types)

Unserved areas where there is no network coverage at all

For example,if mobile operator will place a cell sites in an urban area, since the population density will be too high, they consider to place more cell sites than if they place those cell sites in a rural area.

FTTx planers consider to change their ODN (Optical Distribution Network) design entirely depends on they are doing FTTx deployment in Continue reading

I am very glad to announce that Roy Lexmond from my April CCDE training class passed CCDE Practical exam yesterday in France.

Below is his success story and here is his earlier feedback for the class. I should say that He really likes the design and open to learn new things and very clever.

Please join me to congratulate Roy for his great achievement!

On 19th May in France (Paris) I passed CCDE practical exam. My preparation was done with the cisco learning network excelsheet, Ciscolive video’s, internetworkexpert SP&CCDE courses, Orhan Ergun CCDE Bootcamp and www.orhanergun.net. I attended the Orhan Ergun bootcamp in April-May with lots of great people which helped me prepare well. I really think that the bootcamp helped me to focus on key technologies and discuss them with other people (very important for me) and to understand how to approach the exam.

It was a challenge and took me 2 years, my satisfaction is extreme! and learned alot during those 2 years and still learning. My next goal will be CCIE-SP wich covers some great content inline with the topics the CCDE already covered.

Roy Lexmond

Senior Network Engineer at Routz

CCIE#26557/CCDP/CCDE

I promise to Continue reading

Flat OSPF network, or single area OSPF networks are real. In fact most of the OSPF network today deployed, is flat OSPF networks. But how many routers can be placed safely in an OSPF area ? Any number from the real world OSPF deployment ? I will share in this post.

Let me explain what it is first and then will share you some numbers from the real network which I engaged recently.

As you might know, OSPF has two levels of hierarchy. Backbone and Non-Backbone areas.

Why Non-Backbone Areas are used in OSPF?

The reason is scalability and manageability. At least in theory. I don’t see so many multi area OSPF design though I teach in very detail in my CCDE classes. But that is for the exam purpose.

There are some very large scale networks use OSPF for scalability, so, IP but satellite (Sometimes called an Access POP) POPs are in Non-Backbone area they place.

But there is manageability aspects of having multi area OSPF design. They group their slow speed access and metro or aggregation networks in different OSPF areas and place high speed backbone/core routers in a backbone OSPF area (Area 0).

But, we generally forget Continue reading

CCDE Study Guide – Are you looking for a book that will teach you all the topics on advanced technical networking? If so, I would be very pleased to recommend CCDE Study Guide written by Marwan Al-Shawi to you.

As one of the professionals who contributed immensely to this book, I must admit that Marwan wrote this book in collaboration with a number of savvy designers. IT experts who contributed to this wonderful book include Russ White, Andre Laurent, Denise Fishbourne, Ivan Papeljnak, and Orhan Ergun. In fact, all the IT concepts in this book are enlightening! The book has many drawings, which will assist learners to understand network design.

Today, I spoke with one of my old friend, an expert in CCDE, who read Marwan’s book, and his comment was this: “The book contains pictures that explain a thousand words.”

The most important topics of the networking design, especially for the CCDE exam, are layer 3 technologies such as IGP, BGP, MPLS, Inter-AS MPLS, and IPv6 and VPNs. These topics are extensively covered in this book.

These topics are very important because CCDE exam is a layer 3 infrastructure exam and because these technologies provide an Continue reading

I would like to share with you every week some networking resources , can be video , article , book , diagram , another website etc.

Whatever I believe can be useful for the computer network engineers, mobile network providers, satellite engineers ,transmission experts, datacenter engineers, basically whatever I am interested in and I like, I will share in a blog post.

There will not be any order of importance among the resources. You can open and go through anyone you want.

I will try to limit the list with 5 resources as I want you to read the posts that I publish on the website. Sometimes can be more than 5 though!

Let’s get started!

TCP vs QUIC – Quic is a new transport protocol I think everyone should have a look at. What are the high level differences between them etc.

TCP vs QUIC: A New Transport Protocol

2. Below post explains how BGP As-Path prepending , when it is done more than couple times , can be dangerous for the attacks on BGP information security

Excessive BGP AS-PATH prepending is a self-inflicted vulnerability

3. This presentation is one of the best presentation about BGP Continue reading

When it comes to multi domain or Inter datacenter communication, minimizing the broadcast traffic between the datacenters is an important scaling requirement.

Especially if you are dealing with millions of end hosts, localizing the broadcast traffic is critical to save resources on the network and the end hosts. Resources are bandwidth , CPU , memory and so on.

In this post I will mention how ARP cache is populated in OTV and EVPN technologies and the importance of ARP proxy function.

Classical approach to control broadcast traffic by localizing it within a datacenter is Proxying.

ARP is a good example of broadcast packet and ARP Proxy or Proxy ARP works either based on control or data plane learning.

Idea is, destination MAC address can be learned from the local device which keeps ARP cache and ARP traffic doesn’t have to traffic over datacenter interconnect links.

I said ARP cache can be populated either via control or data plane learning and let me give an example for each one of them.

OTV as a Cisco preparatory protocol advertise the MAC addresses through IS-IS. MAC reachability information is learned via control plane. But OTV doesn’t advertise MAC to IP binding through IS-IS. Continue reading

One of the advantages of EIGRP Feasible Successor is that it speeds up the EIGRP. In fact, if there is a Feasible Successor in the EIGRP network, such network converges faster than OSPF or IS-IS.

• But what is EIGRP Feasible Successor and how can we find EIGRP Feasible Successor?
• If there is EIGRP Feasible Successor, how does EIGRP converges faster than OSPF or ISIS?

In this post, I will explain the answers to the above questions.

EIGRP Feasible Successor is a backup node that can satisfy the EIGRP feasibility condition.

Feasibility condition simply means that the backup router should be loop-free.

Let’s examine the topology shown below (Figure-1) to understand how EIGRP finds loop-free alternate/backup node.

Figure-1 EIGRP Feasibility Condition

From the Router A’s point of view, Router B and Router C are the equal cost routers; as a result, both ABD and ACD path can be used in the network. What’s more, Router A installs both Router B and Router C not only in the EIGRP topology table but also in the routing table.

There is no backup router in the above topology since Router A uses both Router B and Router C to reach the destination Continue reading

Finally, informational EIGRP RFC 7868 has been published.It is not anymore Cisco’s EIGRP, it is an open standard. Without a most critical feature of EIGRP,can we really say that? Why Cisco doesn’t share the most important feature which can help in large scale EIGRP design although industry has been asking from them for a long time ?

EIGRP RFC 7868 specifies EIGRP Dual Algorithm, EIGRP Packets such as Update, Query and Reply, EIGRP Operation, and EIGRP Metrics (K1,K2,….K6).

And since EIGP is RFC anymore, other vendors can legally implement EIGRP. There was couple of open source EIGRP implementations already,but with the RFC status, seeing new implementations among the big vendors would not be a big deal.

In addition to EIGRP packet types and metric values, there are a couple of important things to understand about EIGRP.

Among them is how EIGRP, as a distance vector protocol, calculates a best path and advertise it to the neighbors.

Understanding what is EIGRP successor, EIGRP feasible successor, EIGRP feasibility condition, metric values and usage in real life deployments is among the most important parameters in EIGRP that should be properly understood.

EIGRP RFC is an 80-page document, which provides detailed Continue reading

BGP Best External is used in Active Standby BGP Topologies generally but not limited with that.BGP Best External feature helps BGP to converge much faster by sending external BGP prefixes which wouldn’t normally be sent if they are not overall BGP best path.

I am explaining this topic in great detail in my Live/Webex “BGP Zero to Hero” course.

There are BGP best internal, BGP best external and BGP Overall best path.

BGP Best external in an active-standby scenarios can be used in MPLS VPN, Internet Business Customers, EBGP Peering Scenarios, Hierarchical large scale Service Provider backbone and many others.

But,How active-standby scenario connection with BGP is created ? In which situation people use active-standby instead of active-active connection ?

Let’s start with the below scenario.

Figure -1 BGP Active-Standby Path Selection Example

First thing you should know that common reason for active-standby or primary-backup link is one link is more expensive than the other.Cost doesn’t have to be a $$ cost only but also be based on latency, performance and bandwidth.

In Figure-1 : IBGP is running in the Service Provider network. Between R1 , R2 and R3 there is an IBGP Continue reading