MPLS Applications, what are the MPLS Applications?. MPLS Applications mean MPLS Services. So what can we do with MPLS basically.

Although the very first purpose of MPLS was fast switching, by the time services/applications with MPLS evolved and there are just so many reasons to use MPLS.

Below are some of the most common use case , or in other words, Applications with MPLS.

Important MPLS applications/services for the network designers are listed below.

VPN – Virtual Private Network is most common overlay mechanism in Networking. We have many of them, GRE, mGRE, IPSEC, DMVPN, GETVPN, LISP, FlexVPNs, MPLS VPNs and so on. But what are the important and fundamentals thing about VPNs?.In this post I will explain some of them.

OPEX and CAPEX are two important network design considerations. From the high level we should understand these two design requirements.

When it comes to Routing Security, BGP Origin and Path Validation should be understood very well.

It is the problem of all, not just large Service Providers. Enterprises, Service Providers, Mobile Operators, basically whoever are interacting with Global Routing.

IRR, RPKI, BGPSEC, Origin Validation and Path Validation are the fundamentals of BGP Routing Security. We have many other posts for the subject on the website but in this post I want to share with you new approach for BGP Path Validation. It is called as AS-Cones.

At the moment, it is still IETF draft but soon it is expected to be Standard RFC.

I discussed it with the inventor of the mechanisms, Melchior Aelmans along with many other routing security topic and decided to share with you!

In the below video, Orhan Ergun, Melchior Aelmans and Jeff Tantsura, discussing new approaches in BGP Security – Path Validation.

They explain ASPA – Autonomous System Provider Authorization , and another approach AS-Cone and they compare those two.

Not only BGP Security Path Validation, but they identify the current known problems of the Global Routing Table/DFZ, such as Hijacks, different types of hijacks, route leaks and they discuss some prevention techniques such Continue reading

Flat/Single Level vs. Multi Level IS-IS Design Comparison. Flat routing means, without hierarchy, entire topology information of the network is known by each and every device in the network.

IS-IS has two levels. Thus, for IS-IS, Multi Level means Two Level IS-IS. Level 1 and Level 2.

When we have two levels, Level 1 routers don’t know the topology of Level 2 and vice versa. By hiding topology information of different level routers, scalability is achieved. Reason we achieve more scalable network is when there is a failure or new information added or metric changes in one Level, another level doesn’t run SPF algorithm.

But what are the design consideration when we have Flat or Multi Level IS-IS networks. Is Multi Level IS-IS design, which mean, Hierarchical IS-IS design always good? Answer is no. Although Multi Level provides Scalability, it comes with extra complexity and end to end routing convergence time increase.

So, I prepared below comparison charts to discuss different design aspects when it comes to IS-IS Single vs. Multi Level design.

If you like this comparison chart, you can see more of them in my CCIE Enterprise Training.

When it comes to fast convergence, first thing that we need to understand what is convergence?

Convergence is the time between failure and the recovery. Link, circuits, routers, switches all eventually fails. As a network designers, our job is to understand the topology and whenever there is qrequirement, add backup link or node. Of course, not every network, or not every place in the network requires redundancy though. But let’s assume, we want redundancy, thus we add backup link or node and we want to recover from the failure as quickly as possible, by hoping before Application timeout.

But what is the time for us to say , this network is converging fast. Unfortunately, there is no numerical value for it. So, you cannot say, 30 seconds , or 10 seconds , or 1 second is fast convergence. Your application convergence requirement might be much below 1 second.

Thus, I generally call ‘ Fast Convergence’ is the convergence time faster than default convergence value. Let’s say, OSPF on Broadcast media is converging in 50 seconds, so any attempt to make OSPF convergence faster than 50 seconds default convergence value is OSPF Fast Convergence on Broadcast media.

There Continue reading

MTL – Multi Technology Lab consist of many technologies in a large topology. When network design is considered, there is no single protocol, many protocols interact with each other. In my CCIE Enterprise Infrastructure Training, I have many MTL (Multi Technology Lab), and students are able to watch the videos, and with the config files, they are able to perform each task in the Lab themselves.

From OSPF, EIGRP to BGP, QoS to Multicast, Layer 2 Technologies to Security, SD-WAN and many other technologies are all in the same lab. Traditionaly these kind of Labs were called as Mock Labs but better term is Multi Technology Lab. If you see on the social media next time one of this labs with OE logo, you know that it is MTL! Let me see your comment

You can check the schedule of next CCIE Enterprise Course by clicking here! 

OSPF is the most common network engineer interview topics without any doubt. Almost all network engineers faced with some OSPF questions in their interview. Thus I thought it is important to cover common questions and the answer with the blog post.

From OSPF LSAs to OSPF Areas, by having Multi Area Hierarchical OSPF for stability, OSPF security and OSPF Fast Convergence, I prepared many questions and explaining them in detail in the below video.

There are many questions in the video and if you liked the video, subscribe to Orhan Ergun YouTube Channel and share your thoughts in the comment section.

Note: OSPF Interview Questions in this video from basics to advanced level and studying this 65 minutes video will enhance your OSPF knowledge definitely!