The Survey of current IPFRR Mechanisms Jozef Papán, Pavel Segeč, Peter Palúch, Ľudovít Mikuš, Marek Moravčík * Faculty of Management Science and Informatics, University of Zilina, Univerzitna 8215/1, 010 26 Zilina, e-mail: {jozef.papan, pavel.segec, peter.paluch}@fri.uniza.sk Abstract — The primary idea of the IP Fast Reroute (IPFRR) technology is to reduce the network recovery time after a link or router failure within an ISP network. The key feature of existing IPFRR mechanisms for reaching low recovery time is the usage of pre-computed alternative backup paths. These alternative backup paths have to be pre-calculated before a network failure will occur. The calculation of the alternative backup path utilizes the specific information about destination networks, and thus most of existing IPFRR mechanisms are dependent on the distance- vector routing protocols (RIP, EIGRP). Other IPFRR mechanisms requires an additional information about the network topology, and therefore strongly depend on the usage of link-state routing protocols (OSPF, IS-IS). The paper is focusing on the analysis of existing IPFRR mechanisms and is identifying and presenting theirs primary problematic areas. Keywords—IPFRR; IP Fast Reroute; Survey; Pre-calculations; Pre-computing; Analysis; I. INTRODUCTION Once a network link or a router failure occurs, a process of the network convergence begins. During the network convergence process affected networks are experiencing serious connectivity problems, where different destinations could become unreachable. This may cause many other difficulties, as for example for time critical services (such as Voice over IP). To address these problems Fast Reroute (FRR) mechanisms has been developed. The first FRR mechanism was developed for the Multiprotocol Label Switching (MPLS) technology [1], and it uses explicit backup path. The research of IP Fast Reroute (IPFRR) mechanisms suitable for IP networks have begun immediately. The strategic goal of all existing IPFRR mechanisms is to achieve a very short failure recovery time after the failure of a link or router is detected. Existing IPFRR mechanisms are actually able to reach the network recovery time up to 50 milliseconds [2] [3]. The restoration of communication by means of a IPFRR mechanism is significantly faster as the process of the network convergence managed by means of a routing protocol itself(see Fig. 1) [4][5]. 20 - 50 500+ time [ms] 200 0 The IP Fast Reroute repair The routing protocol repair Fig. 1. Comparison of IPFRR and routing protocol repair time Significant portion of the overall network recovery time is the time, which is required detect the failure itself. Therefore be able to achieve a fast network recovery time one of the main activities is fast failure detection and a need to minimize the time of the main failure detection process [2] [3].Actually we identify several types of failure detection mechanisms that could be classified as:  Independent detection mechanisms, such as the Bidirectional Forwarding Detection protocol (BFD) [6].  Physical detection mechanisms, such as loss of light, loss of carrier, increase in bit error rate, etc. [2].  Routing protocol detection mechanisms, such as hello mechanisms [2]. IPFRR mechanisms may incorporate mentioned detection mechanisms, which reduce the failure detection time to few milliseconds. Once a fast failure detection mechanism detects the failure of a link or a neighboring router, the router will remove from its routing table all paths, which depends on the failed link or next hop router. Than the IPFRR mechanism will provide the router with alternative routing information, which will be used as an alternative pre-calculated path to bypass failed link or router (see Fig. 2). The alternative backup path must not traverse via failed link. Alternative IPFRR path Primary path S D N Fig. 2. The IP Fast Reroute mechanism