Orhan Ergun No Comments

What is IRU ? Indefeasible Right of Use ?

What is IRU (a.k.a Indefeasible Right of Use)  ?  If you are working in the Operator, Service Provider or Telco/Carrier networks, you probably heard this term. If you haven’t, you need to learn it. Read more

Orhan Ergun 3 Comments

Interdatacenter broadcast control – ARP Proxy in OTV and EVPN

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.  Read more

Orhan Ergun 1 Comment

Should I use Cisco OTV for the Datacenter Interconnect ?

Should I use Cisco OTV for the Datacenter Interconnect? This question comes from not only from my students but also the companies which I provide consultancy.

I will not go through the OTV details, how it works, design recommendations etc. But let me remind you what is OTV and why OTV is used , Where it makes sense very briefly.  Read more

Orhan Ergun 2 Comments

What is VLAN Load Balancing?

In layer 2 switching, the Ethernet frames should be received from the same port where it was sent, otherwise layer 2 switching or switching loop occurs.

Let me explain this concept with the topology depicted below (Figure -1).


vlan load balancingFigure -1 VLAN load balancing

In the above figure, either Port 1 or Port2 is used to send the traffic, and the same port should be used to receive the traffic. The switches use MAC addresses to process the Ethernet frames. Read more

Driss Jabbar 8 Comments


VXLAN EVPN – VxLAN is an overlay technology that encapsulates a Layer 2 frame into UDP header to extend your Layer 2 domain over a Layer 3 underlay infrastructure. Within the UDP header, there is VxLAN header, within this header you have a VxLAN Network identifier (VNI) represented by 24 bits, it means that you have more than 16 million logical networks (recall that you can configure up to 4096 VLANs only)



The idea behind developing such kind of technologies is to overcome some business and technical requirements in todays’ Datacenter architectures such as:


  • Datacenter interconnect, workloads live migration.
  • Using infrastructure resources efficiently and getting rid of any scalability issues related to Spanning tree or VLANs number.
  • Limiting resources consumption due to flooding symptom.


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Orhan Ergun 1 Comment


HSRP VRRP GLBP Comparison– In this post I am going to cover the similarities and the differences between HSRP VRRP and GLBP protocols.

All these technologies provide first hop redundancy for the hosts.

I will use the below table for HSRP VRRP GLBP Comparison and the design attributes listed in it.

For the more technology comparison tables such as MPLS , Quality of Service , Multicast, VPNs , Security and more please click here.


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Orhan Ergun 3 Comments

Common Networking Protocols in LAN, WAN and Datacenter

Spanning Tree, Link Aggregation , VLAN and First Hop Redundancy protocols are used in Campus, Service Provider Access and Aggregation and in the Datacenter environment. There are definitely other protocols which are common across the Places in the Networks but in order to keep this article short and meaningful I choose these four. Read more

Orhan Ergun 1 Comment

Bridging, Provider Bridging, Provider Backbone, and Shortest Path Bridging

I received an interesting comment to my last post on networkcomputing  It was about Avaya’s SPB and how it served in the core of the network at the Sochi Olympics.

For those who are not familiar with acronym, SPB stands for Shortest Path Bridging and it is used for large scale bridging in the data center (Though it is not limited to datacenter environment).

Since the Idea behind of SPB is removing the Spanning Tree protocol and benefits from multipathing which can be easily achieved with layer 3 routing, with SPB,bridging can be implemented in a smarter way. Also better resiliency is achieved with SPB compare to the classical bridging.

In this post I will explain large scale bridging, layer 2 multipathing technologies, some vendor implementations such as Fabricpath of Cisco , SPB of Avaya. I will mention their pros and cons as well. Before going technical details of these technologies, let’s examine traditional/classical bridging, let’s see how large scale bridging problem is solved while examining resiliency and multipathing capabilities of each solution.

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Orhan Ergun 4 Comments

Active-Active Data center Design Models

Active-active data center design can be accomplished in many ways.

You want to have best possible data center design, don’t you  ?

I will mention from some technologies which are used in an active-active data center design at the end of this article.

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Orhan Ergun 1 Comment

What does East-West and North-South Traffic mean ?

East-West and North-South is the traffic pattern of an application in the context of a datacenter.

Applications residing in the datacenter can be built in many tiers. Three-tier application architecture is well known and commonly deployed by the application developers.

For smaller application deployments, two tier is not uncommon and for static , very small web server deployment, only one tier ( one or more server ) might be serving for web, business logic and database processes.


3 tiers application

Figure-1 Three tiers applications

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Orhan Ergun 2 Comments

Introduction to Disaster Avoidance

Companies have to protect their business critical applications. Avoiding data loss and downtime for the mission critical applications is extremely important.

Consider a scenario in which you have been informed that a storm is coming and will hit your datacenter. Read more

Orhan Ergun 1 Comment

Introduction to Disaster Recovery

Businesses want to choose reliable equipments, components and technologies while designing a network. You may deploy most reliable equipments from your trusted vendor or deploy most mature technologies with carefully do not forget eventually every system fails !

Depends on where is your datacenter located, different disasters may happen. For U.S  storm, tornado is not uncommon. I remember just couple years before because of major flooding, Vodafone couldn’t serve to their customer in Turkey for at least 1 day.

Disaster Recovery 2

Thus, resiliency is an important aspect of the design plan.Resiliency means, how fast you can react to failure with the simplest explanation.

Disaster recovery is the response and remediation that a company follows after a planned or unplanned failure. Businesses often have a secondary datacenter used mostly for backup. If the company has multiple datacenter, they can be used as active/active though.

Secondary datacenter can take the responsibility in the case of a primary datacenter fails if it is used as backup.

Recovery time will depend on business requirements.For the mission critical applications, business may tolerate very short if not zero down time. Then the cost of the required equipments in primary and backup datacenters, skilled engineer who can manage that design, complexity of the design changes based on the expectation of business from the disaster recovery service.


The amount of data loss a company can tolerate, also known as its recovery point objective (RPO) is a very important parameter. Recovery time can be between 2 hours to days or even weeks, based on the company’s applications. Highly critical applications require less downtime and less data loss. For that reason, a disaster avoidance solution might be a better option for businesses with many highly critical applications.