Segment Routing Traffic Engineering

Segment Routing Traffic Engineering - First, you need to remember MPLS-Traffic engineering operation. MPLS-traffic engineering requires four steps, as shown below, for its operation. Link information such as bandwidth, IGP metric, TE metric, and SRLG is flooded throughout the IGP domain by the link state protocols.

The path is calculated either with CSPF in a distributed manner or with offline tools as a centralized fashion. If a suitable path is found, it is signalled via RSVP-TE and the RSVP assigns the label for the tunnels. The traffic is placed in the tunnels.


Figure - IP MPLS Traffic Engineering

In the diagram shown above – if the traffic flows between R1 and R5 when the packet travels to R2 – the IGP chooses the top path as the shortest path. This is because the cost of R2 to R5 through R3 is smaller than that of R2 to R5 through R6. As you must have observed, R2-R6-R7-R4 link is not used during this operation.

With MPLS-traffic engineering, both the top and bottom path can be used. The top path has high latency and high throughput path; as a result, it can be used for data traffic. On the other hand, the bottom path has low latency, low throughput path, and expensive link; thus, it can be used for latency sensitive traffic, including voice and video. To complete this operation, we need to create two MPLS-traffic engineering tunnels: one tunnel for data and the other tunnel for voice traffic. After doing that, we can place CBTS (Class based traffic selection) option of MPLS TE and voice traffic into voice LSP (TE tunnel).

Next, we can identify data traffic and place it into LSP (TE tunnel). How can we achieve the Traffic Engineering operation with Segment Routing? Segment routing traffic engineering I have explained Node/Prefix SID in one of the previous sections. Now, you know that Node/Prefix SID is assigned to the loopback addresses of all segment router enabled devices, and SID is unique in the routing domain.

Also, there is another SID type flooded with IGP packet. Adjacency Segment ID While Adjacency SID is unique to the local router, it is globally not as unique as Node/Prefix SID. Routers automatically allocate an Adjacency Segment ID to their interfaces, especially when the segment routing is enabled on the device.

    In the topology shown above, R2 allocates Adjacency SID to the interface of R6. Label 22001 is the adjacency SID of R2 towards R3 interface, and it is used for steering traffic from the shortest path (perhaps, you do not desire to use only the shortest path). Label 16005 is the Node/Prefix SID of R5. If the packet is sent from R1 to R5 with two SID, 22001 and 16005 (since R2 usually send 22001 for its local adjacency), R1 will send the packet to R2; R2 will pop 22001, sending the remaining packet towards R6 with16005 – which is Node/Prefix SID of R5. R6 will send the packet to R7 because it is the shortest path to R5.

Node/Prefix SID is used in the shortest path routing, and it has ECMP capability. What’s more, Adjacency SID is used in explicit path routing. NOTE: While Adjacency SID is used for Explicit Path Routing, Node/Prefix SID follows the shortest path. I will provide more examples so that you can understand how to use node and Adjacency SID to provide an explicit path for the traffic flows.


Figure - Node and adjacency segment id

Our aim is to send traffic between router A and router J; however, we do not want to use E-G link. In this operation, we will use the A-C-E-F-H-J path. To achieve our aim, we need to reach E. After that, we will divert the traffic to the E-F link. Next, F will transfer the traffic to J, which is the final destination. Router A should put three label/Segment ID on the packet.

SID 1600, the first SID, will travel to router E. The second SID is 16002, which is the Adjacency SID for the R2-R3 interface. This SID is unique, and it is known only by the ingress router, not by C. The third SID is 16003, which is the Node/Prefix SID of Router J. Router C receives the packet with three SID, pops the 16001, and sends the remaining two labels to router E. Router E receives the packet with 16002 SID, which is the Adjacency SID towards router F. Thus, router E pops it, and sends the remaining packet to router F.

Router F receives the packet with SID 16003, which is the Node/Prefix SID of router J. So, router F follows the shortest path, sending the packet to router H as well as swapping 16003 with 16003 without changing it. If router J sends implicit null label, router H pops the 16003 and undergoes PHP, sending the IP packet to the router J. If we want to carry out this operation using MPLS-TE, we can create an explicit path by providing ERO. Also read : Segment routing fundamentals

Created by
Orhan Ergun

Orhan Ergun, CCIE/CCDE Trainer, Author of Many Networking Books, Network Design Advisor, and Cisco Champion 2019/2020/2021

He created OrhanErgun.Net 10 years ago and has been serving the IT industry with his renowned and awarded training.

Wrote many books, mostly on Network Design, joined many IETF RFCs, gave Public talks at many Forums, and mentored thousands of his students.  

Today, with his carefully selected instructors, OrhanErgun.Net is providing IT courses to tens of thousands of IT engineers. 

View profile

Daniel Lardeux
Daniel Lardeux Senior Network Consultant at Post Telecom

I passed the CCDE Practical exam and Orhan’s CCDE course was very important contributor to my success. I attended the CCDE course of Orhan Ergun in July and it was exactly what I needed, Orhan is taking the pain to break down the different technologies.

Roy Lexmond
Roy Lexmond Senior Network Designer at Routz CCDE #20150017 & CCIE R&S; #26557

After I attended Orhan Ergun’s CCDE course I passed the CCDE practical exam.I really enjoyed the course a lot ...

Nicholas Russo
Nicholas Russo Network Consulting Engineer (CCDE/CCIEx2), Cisc

I signed up for Orhan’s CCDE training. This training is very technically detailed and the use-cases, quizzes, scenarios, and mind maps are all great resources in the overall training program. Orhan teaches his students to think like a network designer ...

Slide Heading
Slide Heading Network Systems Engineer at Conscia A/S CCIE #42544 (SP) & CCDE #20160015

Orhan is forcing you to take off the implementation hat that most of us have been wearing for many years, instead he is providing a new fancy design hat, which makes you see and deal with the issues presented ...

Kim Pedersen
Kim Pedersen CCIE in RS and SP (#29189) CCDE#20170021

I’ve used Orhan’s self-paced CCDE training material. If you are interested in knowing how all the technologies go together in a coherent design i can highly recommend it.I also enjoyed the Quizzes which helped pick out my weak spots in selecting ...

Laurent Metzger
Laurent Metzger 3xCCIE/CCDE Senior Network Architect

Hi Orhan. I passed the CCDE exam on February 22. I read everything that you put on your Self Paced CCDE Training course and it was very helpful in my success. Thank you very much.

Martin J. Duggan
Martin J. Duggan Network Architect at AT&T;, Ciscopress Author CCDE #20160006 & CCIE#7942

I attended Orhan’s April 201610 days CCDE Bootcamp. I am CCDE now !

You can tell Orhan has a great deal of experience, it really comes through when he presents his design case studies and the CCDE Practical scenarios.

Muhammad Abubakar
Muhammad Abubakar Lead Network Architect – CCDE #20160016 2xCCIE #26693 2xJNCIE VCIX

Your excellent CCDE materials and amazing Bootcamp helped me tremendously through my learning journey.Also thank you very much for being available whenever I have a design question or a complex design topics. I can’t compare your design skills ...

Jennifer Pai
Jennifer Pai Network/Security Engineer at KNET Technology

Thanks Orhan very much for this course. It helped strengthen my “Network design mind”.

Ruslan Silyayev
Ruslan Silyayev Solution Architect at R.I.S.K Company

Training by Orhan is not a CCDE preperation training only. It will be useful for engineers which are dealing with design. You want to pass CCDE exam or learn network design, then don’t look at anywhere else!

Sameer Meher
Sameer Meher Solutions Architect at 23 Wards/Japan

Orhan Ergun’s CCDE course was really very good. CCDE Level Intelligence was delivered very well and with very useful case studies and the scenarios, I am thankful to Orhan for all his help!

Ken Young
Ken Young Senior Technical Architect Province of Nova Scotia, 2xCCIE #41597 | CCDE #20170047

If anyone wants to understand network design and architecture, also pass CCDE exam , I recommend you to attend Orhan’s online courses! I am a CCDE now but learning is a journey, we will be together in your other courses too Orhan!

Matt Cross
Matt Cross Technical Architect at Heartland – CCDE #2019::7

Orhan did an excellent job of filling in the gaps of knowledge that I had that took me to the finish line of the practical exam CCDE. The community of people that Orhan facilitates are both engaging and supportive of the journey to CCDE. Orhan ...

Shiling Ding
Shiling Ding Sentinel Technologies – CCDE #2019::12

Just passed the CCDE Practical exam! I attended Orhan Ergun’s CCDE training program , used Orhan’s Instructor Led and Self-Paced CCDE training and Online CCDE Practical Scenarios during my CCDE journey. Orhan’s CCDE In Depth book is an excellent summary ...

Abelardo Basurto
Abelardo Basurto Solutions Architect at Cisco Systems – CCDE 2018::6

Hi everyone, I’ve just passed the CCDE Exam. My Number is CCDE 2018::6 I attended to Online CCDE Bootcamp of Orhan. I want to thank Orhan not only for the great book and bootcamp, but also for his commitment, availability and willingness to assist the ...

Hady Mohamed Abdellah
Hady Mohamed Abdellah Network Architect Hamad International Airport Qatar – CCDE 2018::1

Hi guys, I’m so happy that I passed the exam. I’ve already got my number CCDE 2018::1. Thanks to Orhan for being the best CCDE instructor in the world. I highly recomend Orhan’s CCDE Training and In-Depth-CCDE ...

Bryan Bartik
Bryan Bartik Sr. Systems Engineer at CompuNet – CCDE 20170059

Hi Orhan I passed CCDE Practical exam on November 2017 ! I really enjoyed your materials and quizzes and use cases. They were definitely helpful in my preparation. Thanks a lot !

Giedrius Trapkauskas
Giedrius Trapkauskas Network Solutions Architect at Liberty Global – CCDE 20180004

I attended Orhan’s CCDE Training in Istanbul and it was very helpful in my preparation. I passed the exam recently and I want to say Thank you Orhan! For those who want to pass the CCDE exam, definitely start with ...

Alaa Issa
Alaa Issa Sr.Solutions Architect – CCDE#20180033 3xCCIE ( Collab|DC|Security )#27146

I registered to Orhan’s training in Feb 2017. From that time, I attended Orhan’s training several times. The depth of knowledge which Orhan has is amazing, and how to present such consistent knowledge to the ...

Mazin Ahsan Design Lead Engineer | Solutions Engineer | CCDE License # 20160030 | CCIE Licence # 23892

I passed the CCDE Practical Lab exam on November 17,2016 from supplications of elders and dedication from my Sensei Mr. Orhan Ergun I took different CCDE bootcamps in the past. Orhan has the most depth and expertise ...

Jeff Patterson CCDE# 2018::11

Hi Orhan I wanted to pass along my appreciation for the outstanding training material. I used the online CCDE training provided by Orhan as well as the In-Depth-CCDE book and passed the exam in February 2018. Thank you Orhan!

Mehdi Sfar
Mehdi Sfar Network and Security Architect / CCDE #20210003 | CCIE R&S; #51583

I signed up for Orhan’s CCDE Self paced Course. This course, along with the CCDE In Depth book, helped me for my CCDE Practical as well as Written exams. It pushed me to ask the "WHY" questions and allowed ...

Related courses

Segment Routing Training

11:26:03 Hours
31 Lectures


MPLS Zero to Hero Training

30:07:04 Hours
51 Lectures


Cisco CCIE Service Provider Training

108:43:00 Hours
258 Lectures