Why the Fuss About MPLS?

mpls-iconIf you want to be blown away with an MPLS text, check out MPLS-Enabled Applications: Emerging Developments and New Technologies. While not a required component for my CCIE R&S Training Part 4 course, it would be a nice supplement.

I am going to use this excellent text as the foundation for a series of blog posts that I consider to be most important for CCIE R&S and SP students as they seek to master MPLS.

One of the first questions we should ask, is why MPLS? What issues can it solve? Well, the first IETF MPLS Working Group Meeting occurred in April of 1997. At that meeting, the engineers identified four main items they sought to address with the new technology:

  1. Scalability of network layer routing– this refers to the ability to aggregate forwarding information using labels. This is clearly witnessed today in the most popular application of MPLS technologies – the Layer 3 VPN. I love to watch the amazement on student’s faces when they build an L3VPN for the first time. They are initially bewildered by the BGP-free core that results, and the fact that no router in the topology requires full route information for all of the prefixes in the scenario. For many students, it is at this moment they embrace the inclusion of MPLS in their lab and written exams.
  2. Greater flexibility in delivering routing services– this refers to the use of labels to identify traffic that is to receive special service and pathing not based strictly on destination-based forwarding. While not a requirement for R&S track students, this gives rise to DiffServ Aware Traffic Engineering and is a concern for SP students.
  3. Increased performance– refers to optimization of network performance through a new, simple paradigm of label-swapping. In his excellent book,MPLS Fundamentals for Cisco Press, Luc De Ghein refers to this as the “bogus benefit” of MPLS. He points out that thanks to technologies like Cisco Express Forwarding, the performance gains with MPLS are negligible. But Minei and Lucek quickly point out in MPLS-Enabled Applications that the performance gains of MPLS should be viewed in a greater context than just individual nodes. When one considers traffic engineering and fast rerouting of traffic in the network as a whole, performance gains thanks to MPLS are certainly significant.
  4. Simplify integration of routers with cell switched based technologies– in April of 1997, many networks features a core of ATM switches surrounded by routers that were fully meshed with ATM connections. As we know, full meshing router connections gets out of hand real fast, so the idea was to allow the ATM devices to peer with routers. Today the problem has actually changed. More and more networks feature an MPLS core, with ATM switches interconnected via Layer 2. Now the number of adjacencies for ATM switches is the issue. This has all led to work on Generalized MPLS (GMPLS). This is the idea of a common control plane that covers a vast scope of devices such as routers, ATM switches, SONET/SDH equipment, optical cross-connects, etc. More information on this concept can be found inRFC 3945, Generalized Multi-Protocol Label Switching (GMPLS) Architecture.

For R&S candidates in particular, I think understanding the rationale behind MPLS technology is critical before delving into detailed study. I hope you will join me for more blog posts on key MPLS technologies.

10 thoughts on “Why the Fuss About MPLS?

  1. Hello Anthony,

    This would be my first post on your blog and I would like to say, first of all, what a great job you’re doing and I appreciate it.

    Also, I just recently embarked on the journey to becoming CCIE certified and have decided to ensure that I have an in-depth understanding of everything in the blueprint and the certification guide and as such, I would like to ask permission if it’s okay to drop my questions in the comments section of your posts as I don’t have any means to contact you directly (if it would be possible to reach you directly, it would be awesome).

    So, here’s my first question, When configuring the destination IP address in ERSPAN, do you use the IP address of the sniffing station or the closest layer 3 interface connected to the station (assuming the station is connected to a low end layer 2 switch that is then connected to a router)?


  2. Hello Anthony,

    Re: CEF – since I don’t see this explicitly listed as a topic in the CCIE LAB requirements, to what extent do I need to know it for the LAB?

    Thanks in advance!

    1. It would be a written thing more than anything else. For the lab – we just always make sure it is on (which it is by default) since so many features require it.

  3. Anthony,

    TL;DR what are the differences (pro and cons) of L3 vs MPLS forwarding.


    I’m currently studying JNCIA-Junos JN0-102 (well that a mouthful) through CBT Nuggets. In video 5 (layer 2 and layer 2.5) you mention MPLS.

    I’m trying to wrap my mind around the concept of MPLS. So far I understand that it uses frames instead of IP headers to forward traffic. Furthermore since you don’t look at
    layer 3 you could set up L3VPNS and run IPv6 traffic through an IPv4 MPLS cloud in-case you don’t want to doublestack or set up teredo tunneling.

    But still why would you use it besides these specific cases today when you got L3 forwarding based on IP which seems less complex and when issues with routing tables which was eating up precious RAM doesn’t seem to much of problem anymore.

    Finally to what extend do you need to know L2.5 for JNCIA-Junos JN0-102

    1. MPLS is kind of like the Swiss Army Knife of networking right now. It is being used for many different purposes by many different entities. By far, the most popular usage still today, however, is the Layer 3 MPLS VPN. Here is an article that discusses the pros and cons of these structures. Read each bullet post carefully, they contain a ton of great information. http://codeidol.com/community/telecom/advantages-and-disadvantages-of-mpls-layer-3-vpns/7515/

      I wish the JNCIA exam tackled this more in depth. Sadly, you can expect about one question total in your exam and it will be VERY high level.

      Finally, if your interest is peaked about MPLS, check out the CCIE course on VPNs which covers it and a lot more – https://www.cbtnuggets.com/it-training/cisco-ccie-rs-v5-all-in-one-4-0-vpn-technologies

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