BGP PIC Edge - Prefix Independent Convergence

BGP PIC Edge provides sub second convergence time in the case of edge link or node failure. BGP PIC is a useful for MPLS VPN service and can be provided by the Service provider as a value added service thus might provide additional revenue. BGP PIC provides sub second converge time in case link or node failure, and BGP PIC edge covers the edge failure cases.

Sub second convergence is not possible without PIC – Prefix Independent Convergence for BGP.  

I am explaining this topic in deep detail in “BGP Zero to Hero” course.


Figure -1 BGP PIC (Prefix Independent Convergence) Edge

In order BGP PIC Edge to work, edge IBGP devices ( Ingress PEs and ASBRs ) need to support BGP PIC and also they need to receive backup BGP next hop.  

In the above topology, R1 is the ingress PE, R4 and R5 are the ASBR nodes.Route Reflector is shown in the data path but it is not recommended in real network design.  

Unfortunately backup next hop is not sent when BGP Route Reflector is introduced since RR selects and advertise only the best path for the given prefix.

For example, in the above topology, R6 and R7 both sends, network but R1 can learn from the RR only one exit point (BGP next-hop), either R4 or R5.   

There are many ways to send more than one best path from BGP RR but let’s not talk about them in this article, instead let’s assume, R1 learns the prefix from R4 and R5.  

How BGP PIC Edge Works ?  

Let’s assume link between R1 learns the prefix from R4 and R5 and choose the best exit point as R4. In this case R5 is marked as backup/alternate next hop and programmed into the FIB (Forwarding Information Base) of R1.  

Let’s examine some failure and see how BGP PIC takes an action.   – BGP PIC edge in case of edge link fails but ASBR doesn’t set next-hop self-  

In case R4-46 link fails and R4 doesn’t set next-hop to itself (No next-hop self). In that case, link between R4 and r6 is advertised to the IGP. When R4-R6 link fails, R1 learns the failure from the IGP. BGP Next-hop tracking feature helps here.

IGP protocols register to the BGP Next-hop tracking process (Similar to IGP to BFD registration right ? )  

When R1 learns the link failure between R4-R6, it immediately changes the BGP next hop for the prefix to the R5. This switchover is done in less than a second regardless of the number of prefixes. Which mean even though you have million of BGP prefixes which need to be updated, still sub second convergence. (In this example for the simplicity only prefix)   – BGP PIC edge in case of edge link fails and ASBR set’s next-hop self –  

When R4 sets BGP next hop to it self (It is done by setting the loopback as next-hop), since the loopback interface won’t go down, even though R1 learns the link failure (if the R4-R6 link is redistributed into IGP) from IGP, it doesn’t trigger BGP next-hop tracking to fails the BGP next hop , because BGP next hop for the prefix is not the R4-R6 link address but the R4 loopback.

In this case R1 continue to send the traffic for the prefix to the R4. But since the link between R4-R6 fails, when R4 receives the traffic destined to, it should send towards R5 immediately. (That’s why in the beginning I said, not only Ingress nodes, but also ASBRs should learn the alternate next-hop)  

When do you set next-hop self on the edge BGP node ?

In MPLS VPN environment it is the best practice and almost mandatory to set the BGP next hop to the PE loopback. With that, transport LSP can be created to that PE loopback. So far in the examples, BGP PIC edge protected the link failures.   – BGP PIC edge in case of edge node failure –   What if R4 fails ? How R1 would reach to that failure ?  

In case R4 fails, IGP will trigger the BGP Next-hop tracking and R1 can change the next-hop as R5 for all the BGP prefixes. Convergence is again sub-second regardless of a number of BGP prefixes.   

BGP PIC Edge Conclusion :

  • BGP PIC – Prefix Independent Convergence is a BGP data plane convergence mechanism , not a control plane. Thus convergence time is only related with IGP convergence and prefix independent. If you have 500K full internet routing table, all of them will be installed in the FIB before the failure as a backup route and when the failure happens, next BGP next hop is used immediately.
  • BGP PIC is also known as BGP Fast Reroute.
  • BGP PIC is very suitable for MPLS VPN service, especially when the customer pay and ask tight convergence time in any failure.
  • When BGP PIC is enabled, adding backup path for the million pf prefixes require additional memory and CPU, thats why resources should be monitored carefully
  • BGP PIC is not necessarily only a BGP feature though. Since BGP can take advantage of recursion, hierarchical data plane arrangement. It is also not a Cisco proprietary protocol, most of the vendors implement BGP PIC today, Juniper is implementing BGP PIC as well, you can read it from here.
  • In an IP environment without tunneling (GRE, L2tpv3,IPinIP) or encapsulation (MPLS) intermediate nodes which are not converged yet would send the packet back to R4 since they would think that R4 is still reachable so it would be temporary loop. In the case of MPLS or other tunneling mechanisms intermediate nodes wouldn’t need BGP so they would just send packet to second best path as per the R4 request.

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

Cisco CCDE v3 Training

71:39:34 Hours
225 Lectures


BGP Training

22:46:48 Hours
22 Lectures


Cisco CCIE Service Provider Training

108:43:00 Hours
258 Lectures