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Design considerations for network mergers and acquisitions

Network mergers and acquisitions are the processes which can be seen in any type of businesses. As a network designers, our job to identify the business requirements of both existing networks and the merged network and finding best possible technical solutions for the business.

There are many different areas which need to be analyzed carefully. Wrong business requirement gathering and design analyze, definitely lead to catastrophic failures.

Business and network analysis and technical information gathering are the key steps and there are many questions which need to be asked and answered should be well understood.

Network mergers and acquisitions is also called as Network integration.

Below are the key points for any type of network mergers and acquisitions projects.

  • Business analysis and information gathering

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OSPF Multi-Area Adjacency | OSPF Area Placement | RFC 5185

OSPFv2 by default setup only one adjacency over a single link. But this can be an issue some time and as a network designer you should understand the consequences and know the available solutions.

Placing a link in wrong OSPF area can create an OSPF sub optimal routing especially in hub and spoke topology.

In IS-IS or OSPFv3, this wouldn’t be an issue because IS-IS and OSPFv3 allow link to be placed in more than area or level. (In IS-IS, area is assigned to the router, not to the link. Thus I use level keyword)

Let’s look at the below network to understand what is the issue and how OSPF multi-area adjacency can solve the sub optimal routing problem. Read more

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IS-IS Design considerations on MPLS backbone

IS-IS Design considerations on MPLS backbone

Using IS-IS with MPLS require some important design considerations. IS-IS as a scalable link state routing protocol has been used in the Service Provider networks for decades.

In fact, eight of the largest nine Service Providers use IS-IS routing protocol on their network as of today. Read more

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BGP Peering – Private, Public, Bilateral and Multilateral Peering

BGP Peering

BGP Peering is an agreement between different Service Providers. It is an EBGP neighborship between different Service Providers to send BGP traffic between them without paying upstream Service Provider.


To understand BGP peering, first we must understand how networks are connected to each other on the Internet. The Internet is a collection of many individual networks, which interconnect with each other under the common goal of ensuring global reachability between any two points.


BGP peering
BGP Peering and Transit Links

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What is reliability in networking ?

What is reliability in networking ? Why reliability is an important design tool ? I will provide the answers of these questions with the examples in this post.

Reliability is within the reasonable amount of time, which depends on the application type and architecture, delivering the legitimate packets from source to destination.

This time is known as delay or latency and it is one of the packet delivery parameters. Consistency of delay known as jitter and it is very important for some type of applications such as voice and video, jitter is our second delivery parameters.

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BGP Next-Hop Behaviour in IP and MPLS Networks

One of my CCDE bootcamp students asked a question about next hop in MPLS VPN network. So, I would be very pleased to explain the BGP next hop behaviour both in IP and MPLS network in this post.

Let’s start with this IP network shown below (Figure-1).

IBGP next-hop

Figure-1 IBGP Next Hop handling in IP networks

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How fast is your network?

You always wonder how fast is your network, right? How long does it take the information travel over the network?

I will share with you this special article, which you can use to find the speed of your network and define it with a numerical number.

I will use ring, partial mesh and full-mesh physical topologies to explain the concept.

Note : I assume bandwidth of all the links in the examples are the same for simplicity.

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Pim Sparse Mode

Pim sparse mode – Multicast is used to send the data to the multiple receivers at the same time. Multicast reduces the load on the servers (Senders/Source in multicast term), provides efficient capacity usage on the network links.

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MPLS Design Case Study

MPLS Design – MPLS Design Case Studies are the useful resources to learn the design details of MPLS.

You will be provided a brief information about the business and technical requirements. You can share your answer at the comment section below.

Note: This is only one of the case studies in the DesignWorld.

DesignWorld provides video and written content for the network designers.

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EIGRP vs OSPF  – Below comparison table is your primary resource for the OSPF and EIGRP routing protocols when you compare them from the design point of view.

Knowing and understanding these design practices will not only help you for the real life network design but also will help for the any design certification exams.

If you have any question regarding the parameters in the comparison chart, please share in the comment so I can provide more information.

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MANET: Mobile Ad Hoc Networks

The MANET stands for mobile ad hoc network; in practice, the term generally applies to ad hoc wireless networks of sufficient complexity that some internal routing mechanism is needed to enable full connectivity.

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Single Vs. Dual Carrier Design

Companies don’t always have high availability. What’s more, there is always a concern of budget and complexity with the high availability even though a number of factors need to be considered during network design.

If the applications of the company do not require high availability, dual carrier or two links to the same carrier is not necessary.

Multihoming refers to a connection to the two different carriers/service providers even though two routers via two links to the same provider is not considered multihomed.

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IS-IS Suboptimal Routing Design

If you design multi level IS-IS network and if you have more than one exit (L1-L2 routers) from the Level 1 domain, you will likely create a suboptimal routing. Multi-level IS-IS design is for large-scale network. What’s more, most of the real life networks use only flat Level 2 IS-IS as their interior gateway protocol (IGP).


is-is routing protocol


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IGP LDP Synchronization

I implore all my readers to always remember this topic: IGP LDP synchronization. It is important to use IGP LDP synchronization to avoid blackholing, especially when MPLS networks fails to function effectively.


igp ldp synchronization


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Routing design

Understanding everything about routing design is no brainer, especially if you have the chart below on your wall.

The table below highlights the pros and cons of each routing protocol. Of course, you need to consider the design attributes shown in Figure A before embarking on routing design.

Should you like the comparison of the routing protocols illustrated in the table below or should you want to see similar comparison for other technologies, feel free to add your comment in the comment section.

Another boon for all my readers!

If you are interested in network design or considering CCDE, CCDP, or CCDA certification, you can subscribe for membership here so that you can peruse all the design resources (Videos , Tests , Case Studies , and E-Books).

Figure A: Comparison of Routing Protocols

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Dual Core Network Design

Dual Core Network Design – Dual core design, also known as dual plane or disjoint plane topologies, refers to a highly redundant network chosen by companies whose main objective is to improve the resiliency of their network. Created using different data planes, dual core design is implemented by companies that receive the service from the different service providers. Put simply, big companies use dual core design in order to improve their network. Institutions that generally use this design are found in Europe; they include banks, hospitals, and other financial institutions. What’s more, some companies outside Europe use this design.

The links – passing through same fiber conduit, building, town, or city – are identified as Shared Risk Link Group (SRLG) since they share the same fate if there are any technical glitches. It is pertinent to carefully identify SRLG links between the providers. And if there are shared links, diverge links should be demanded.

core network design


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Bad Network Design

Bad Network Design – Availability of  a system is mainly measured with two parameters. Mean time between failure (MTBF) and Mean time to repair (MTTR)

MTBF is calculated as average time between failures of a system. MTTR is the average time required to repair a failed component (Link, node, device in networking terms)

Operator mistakes is widely seen as the source of the failure of the systems. Thus although it is not individually used to calculate availability value of a system, Mean time between mistakes (MTBM) is commonly used term among the network engineers.

Most failures are caused by human error;estimate range between 70 to 80 percent. How can so many people are so incompetent?

Actually they are not ! It’s a design problem.

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HSRP, VRRP and GLBP are the three commonly used first hop redundancy protocols in local area networks and the data center.

In this post, I will briefly describe them and highlight the major differences. I will ask you a design question so we will discuss in the comment section below.

hsrp vrrp glbp

source: Orhan Ergun CCDE Study Guide – Workbook

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Free CCDE Workbook Winners!

Last week I sent a below questions and asked the optimal place for an OSPF ABR (Area Border Router). There was a high level of participation. Thanks everyone who shared their thoughts. Hopefully they didn’t do it only for a free CCDE Workbook prize 🙂


CCDE WorkbookAnswer is Router G or H because

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Your Design Should Be Usable!

Whatever you design , it should be usable first. Computer network design is not an exception.You are not designing a network to support one service only such as VPN or Internet.It should give enough functionality for today and future needs.

Your design should be usable today and the future !

It was so common to use TDM and Ethernet, IP or MPLS as a transport mechanism at the Access and Aggregation network and for the mobile backhaul. TDM is for the real time , delay , loss, jitter sensitive traffic, Ethernet is for the general data applications.

Building a TDM based network is good for real time applications but expensive at the same time. Thus if you will design a converge transport network, you need to understand your business requirements first.

Which services business want to offer ? What are the trends ?

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Network Design Best Practices – Simplicity

Network Design should be simple! Simplicity is the first network design best practice that I want you to remember. If you have been in the field long enough, you have probably heard about the KISS principle.

If you are a regular follower of my blog, you have maybe heard about the SUCK principle as well.

KISS stands for Keep It Simple Stupid. But do you really know what the simple part is ?  Can every part of the network be a simple ?

Unfortunately NOT ! It just cannot be ! But still you should on simplifying as much of your network as possible.

As I have indicated in the past here, intelligence should be at the edge of the networks and network core should be as simple as possible. If you read the above article, you will see some examples. ( There are different opinions about the place of simplicity in networks. Some researchers believe that if the core has some intelligence the overall network complexity is reduced ).

Networks have many protocols, technologies. Understanding each of them might be easy but interaction between them creates complexity.

In my CCDE training sessions, I like to give the Pepper and Salt example to explain this point.

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Root Cause Analysis

Designers should be trained to identify the real issues for customers in computer network designs. Developing an excellent solution for the wrong problem can cause more damage than doing nothing at all. Finding the right issue is vital for assisting customers.

Imagine a customer tells you that they need a CGN (Carrier Grade NAT) solution and wants you to design their network.

Instead of jumping immediately to that solution, you should take time to determine the real issue.

After analysing the problem, you find the customer’s real issue was an IP address exhaustion. Then you come up with a range of solutions that include IPv6, CGN, asking for a new block from registry, existing address redesign.

You should keep in mind the advantages and disadvantages for each solution, and also include possible future benefits and potential issues.

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Orhan Ergun 4 Comments

CCDE Practical Training Demo Video

I have been delivering CCDE practical training for quite some time. Couple months ago I have started a survey for my CCDE training. 134 people voted and here is the results.

ccde practical class

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Orhan Ergun July 2015 CCDE Training

Attention CCDE Practical & CCIE Career Track Candidates!

I am pleased to announce that my next online WebEx CCDE live stream training will begin on July 20th, 2015.
This class will be recorded and distributed to all students for their future review.

This class will not only help CCDE students pass their practical exam, but also aid CCIE candidates fill in knowledge gaps and further their understand of technical concepts and theory.

Course will be delivered over a one month period, 3 days a week, 3 hours per session.
This is to allow the student to digest the information as well as work through the topics presented.
This approach not only aids in your retention of the information presented, but is also HIGHLY cost effective since ancillary training costs (travel and lodging) are nil.
Students may also take future CCDE offerings free of charge until they pass their CCDE.

To find out what previous students are saying about this course (click here).
Success stories of previous students as well as their thoughts on my training versus others (click here).
To watch a sample video module (click here).

What is covered ?

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Why and Where Ring topology is used ?

Ring topology is used mostly for economical reason. It is very common topology in the service provider access, and it is not so uncommon in Aggregation and Core ( Backbone ) networks as well.

Long haul links are expensive thus in order to provide last mile connectivity in the Service Provider access domain, nodes might be connected to the closest nodes which have similar functionality. Read more