ENHANCED FAST REROUTING MECHANISMS FOR PROTECTED TRAFFIC IN MPLS NETWORKS Lemma Hundessa Gonfa UPC. Universitat Polit`ecnica de Catalunya Barcelona (Spain). February, 2003 Thesis Advisor: Prof. Jordi Domingo-Pascual A THESIS SUBMITTED IN FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE Doctor en Inform`atica ENHANCED FAST REROUTING MECHANISMS FOR PROTECTED TRAFFIC IN MPLS NETWORKS Lemma Hundessa Gonfa Thesis Advisor: Prof. Jordi Domingo-Pascual vi To my wife Dr. Truwork whose patience, love, support and encouragement enabled me to complete this thesis and was of great help in difficult times. To my parents for their interest and encouragement of my academic success since a very early age. Finally, to great Samson Gobena and Begashaw, in memory. viii ABSTRACT Multiprotocol Label Switching (MPLS) fuses the intelligence of routing with the per- formance of switching and provides significant benefits to networks with a pure IP architecture as well as those with IP and ATM or a mix of other Layer 2 technologies. MPLS technology is key to scalable virtual private networks (VPNs) and end-to-end quality of service (QoS), enabling efficient utilization of existing networks to meet future growth. The technology also helps to deliver highly scalable, differentiated end-to-end IP services with simpler configuration, management, and provisioning for both Internet providers and end-users. However, MPLS is a connection-oriented ar- chitecture. In case of failure MPLS first has to establish a new label switched path (LSP) and then forward the packets to the newly established LSP. For this reason MPLS has a slow restoration response to a link or node failure on the LSP. The thesis provides a description of MPLS-based architecture as a preferred technol- ogy for integrating ATM and IP technologies, followed by a discussion of the moti- vation for the fast and reliable restoration mechanism in an MPLS network. In this thesis first we address the fast rerouting mechanisms for MPLS networks and then we focus on the problem of packet loss, packet reordering and packet delay for protected LSP in MPLS-based network for a single node/link failure. In order to deliver true service assurance for guaranteed traffic on a protected LSP we use the fast rerouting mechanism with a preplanned alternative LSP. We propose enhancements to current proposals described in extant literature. Our fast rerouting mechanism avoids packet disorder and significantly reduces packet delay during the restoration period. An extension of the Fast Rerouting proposal, called Reliable and Fast Rerouting (RFR), provides some preventive actions for the protected LSP against packet loss during a failure. RFR maintains the same advantages of Fast Rerouting while elimi- ix x nating packet losses, including those packet losses due to link or node failure (circu- lating on the failed links), which were considered to be ”inevitable” up to now. For the purpose of validating and evaluating the behavior of these proposals a sim- ulation tool was developed. It is based on the NS, a well-known network simulator that is being used extensively in research work. An extension featuring the basic functionality of MPLS (MNS) is also available for the NS, and this is the basis of the developed simulation tool. Simulation results allow the comparison of Fast Rerouting and RFR with previous rerouting proposals. In addition to this we propose a mechanism for multiple failure recovery in an LSP. This proposal combines the path protection, segment protection and local repair methods. In addition to the multiple link/node failure protection, the multiple fault tolerance proposal provides a significant reduction of delay that the rerouted traffic can experience after a link failure, because the repair action is taken close to the point of failure. Then we proceed to address an inherent problem of the preplanned alternative LSP. As alternative LSPs are established together with the protected LSP it may happen that the alternative is not the optimal LSP at the time the failure occurs. To over- come this undesired behavior, we propose the Optimal and Guaranteed Alternative Path (OGAP). The proposal uses a hybrid of fast-rerouting and a dynamic approach to establish the optimal alternative LSP while rerouting the affected traffic using the preplanned alternative LSP. This hybrid approach provides the best of the fast rerouting and the dynamic approaches. At the same time we observed that the protection path becomes in fact unprotected from additional failures after the traffic is rerouted onto it. To address this we propose a guarantee mechanism for protection of the new protected LSP carrying the affected xi traffic, by establishing an alternative LSP for the rerouted traffic after a failure, avoiding the vulnerability problem for the protected traffic. Finally, we present a further optimization mechanism, adaptive LSP, to enhance the existing traffic engineering for Quality of Services (QoS) provision and improve network resource utilization. The adaptive LSP proposal allows more flexibility in network resource allocation and utilization by adapting the LSP to variations in all network loads, resulting in an enhancement of existing MPLS traffic engineering. The remainder of this thesis is structured as follows. In Chapter 1, we present the explanation of general MPLS concepts, definition and architecture. In Chapter 2, we present the state of art, the problem of rerouting and the different mechanisms to pro- tect networks from link failures. These techniques range from central to distributed, from simple dynamic local to preestablished global repair mechanisms implemented from the physical layer to the IP layer. In Chapter 3, we propose the enhanced fast rerouting mechanism that reduces the additional packet delay and avoids packet re- ordering during the restoration period on a single link failure in MPLS networks. In Chapter 4, we present an extension mechanism of fast rerouting called the Reliable and Fast Rerouting (RFR) restoration mechanism. This prevents all packet losses during the restoration period while maintaining the previous advantages by using an additional local buffer in each LSR. In this chapter we present a mathematical model for validation of the recovery time and the buffer size needed for the implementation of the proposed mechanism. In Chapter 5, we show the application of the proposed mechanism (RFR) for TCP traffic as well as the effect of link failure in TCP traffic in spite of the reliable transport protocol. Chapter 6 describes a multiple failures tolerance mechanism in a protected LSP. In Chapter 7, we present the proposal that addresses the drawback of the preplanned technique in terms of optimal protection path. At the same time the proposal handles the vulnerability problem for rerouted traffic. In Chapter 8, we present an experimental proposal and preliminary results for a further optimization mechanism that takes into account dynamic changes of network status. Finally, we conclude presenting the summary of our contributions and direction for future work. xii ACKNOWLEDGEMENTS I wish to thank the many people who have, in one way or the other, made this thesis possible. I apologize that I cannot list all the people that I am thankful to. I would like to express my sincere thanks to my director of thesis Professor Jordi Domingo-Pascual, for giving me the opportunity to work in his research group, for trusting in my commitment, for his guidance and encouragement, and finally for the financial funding provided. I would also like to acknowledge Professor Mateo Valero for believe in me, for treating me as if I was one of his own PhD students and for all the help and support extended in requesting financial support from UPC. I am deeply indebted to both of them. I also do not forget that my presence here has been made possible by my former institute, “Instituto Superior Polit´ecnico Jos´eAntonio Echeverr´ıa”, ISPJAE, and thanks also to Dr. Juan Chavez Amarro. I am extremely grateful to Adri´an Cristal, with whom I have discussed several issues in this thesis, especially on the simulation. He allowed me to feel part of his family, likewise to Cristina, Ardiana and Leo. The same to Sanjeevan Kanapathipillai whose help, stimulating suggestions, encouragement, and discussion in many topics helped me in all the time of research to face all kind of adversities. I am grateful to Prof. Eduard Ayugad´e, for guiding me to the appropriate line of investigation in the department according to my interests and for his concern of my studies and situation. I wish to express my gratitude to all members of the Integrated Broadband Commu- nications System Research Group: Xavier, Sergio, Carlos V., Xavi, Rene, Carles K., Albert and especially to Josep Mangues, Jaume Masip, and Dr. Josep Sol´e-Pareta. xiii xiv My life in Barcelona (Spain) would have been much harder if it were not for many friends who helped me on different circumstances. Starting from my arrival at Madrid. Wubalem, Tefera, Yirgalem, Tsegaye, Dereje, Yoseph, Dawit, Mesfin, Robel, Denekachew, Teshome, Meaza, Behailu, Wondifraw, Fitala, Tamrat, Elena, Dinberu, Sonia, Kifle, Constansa, Quino, Isabel, Fernando, Rodrigo, Oscar, Jos´eAntonio, Vero, Douglas, Nori, Paqui, and my distinguish Friday’s football team members de- serve special mention. My stay here has served to value helpful and trusted friends, and provided me the opportunity to meet many good friends. Special thanks go to Nega, Asnake, Daniel Tesfaye, Berhanu Moges, Gashaw, Gosaye, Abebayehu, Gudeta and Kebede for their help, support and friendship. I appreciate the friendship of my fellow researchers: Alex, Alex Ramirez, Beatriz, Blaise, Carlos, Carlos Molina, Daniel, Dany, Germ´an, Javier, Jesus, Jesus Acosta, Jos´e, Lorenzo, Manel, Oscar Ardaiz, Oscar Camacho, Oscar, Lepe, Pedro, Ram´on, Suso, Victor, Jaume, Fernando, Ayose, Oliver, Ruben, Juan Iv´an, Ruben Alvaro, Raimir, Francisco, Larisa, Olimpia, Fran, Xavi, Marco, Carmelo, Alejandro, Amilcar, and system support people (Alex, Xavi, Victor, Joan, etc).