Orhan Ergun 24 Comments

MPLS Design Question

MPLS Design Question – MPLS is one of the most commonly used encapsulation method today. Especially on Wide Area Networks of the Service Providers, Large Enterprises and some datacenters.

Service Providers sell MPLS services to customers for decades. When customers want to have Service Provider redundancy so two MPLS circuit from different Service Providers, Inter AS MPLS service is created between those providers.

Or customers have a location where their MPLS service provider don’t have there but customer wants to have end to end MPLS connectivity between their all locations, again Inter MPLS Service is created between the providers.

If you are a visual learners and want to understand the basics of Inter AS MPLS VPN Options, check my youtube channel and subscribe for the more design videos.

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Orhan Ergun 9 Comments

BGP Design Case Study

Below BGP design case study is taken from the Orhan Ergun’s CCDE Practical Workbook.In the new version of the workbook there are more than 50 case studies are shared for many technologies.

If you are in the network design field or want to learn about it,don’t miss the book.

Scenario :
Network A is a customer of Network Z, Network B is a peer of Network Z.
Network A becomes transit customer of Network B.
Network A announces aggregate to Network Z and more specific prefixes, and to Network B. Network B sends more specific to its peer Z.
Network Z only announces the aggregate to the world. Network B doesn’t announce anything to the upstream SP.

What is the impact of this design ?
Is there any problem ? If there is , how you can fix ? 

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Orhan Ergun 35 Comments


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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Orhan Ergun No Comments

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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Orhan Ergun 99 Comments

OSPF Design Discussion

OSPF Design – In the below picture, where should you place an OSPF ABR (Area Border Router) to scale OSPF design ? Why ?

Please share your thoughts in the comment box below.

First 5 correct answers will get my CCDE Preparation Workbook for free. Please subscribe to email list so I can see your email address for communication.

OSPF Design


Orhan Ergun 30 Comments

VPN Design discussion

In this post, I will give you a business requirements and information about the business of a fictitious company,together we will try to find an optimal solution for the given questions.

There will be many valid solution as you will see from the comments, we will have to make tradeoffs between each design goals while selecting one design vs another.  Read more

Orhan Ergun 25 Comments

VRF-Lite+GRE/dot1q or MPLS L3 VPN

I am going to create a new category on the blog which we will discuss together the different technologies,protocols, designs and architecture.

You can suggest a discussion topics and you all please welcome to join the discussions in the comment box of each topic.

I want to throw a first topic for the discussions !

Which Enterprise Architecture is more complex ? ( Did you read network complexity article in the blog ? )

VRF-lite with GRE/dot1q or MPLS L3VPN ?  Read more