Jean-Jacques Pansiot

An efficient algorithm to enable path diversity in link state routing networks

Multipath routing allows for load balancing and fast re-routing in order to improve the reliability and the efficiency of the network. Current IP routers only support Equal Cost MultiPath (ECMP) which guarantees that the forwarding paths do not contain loops. However, ECMP provides limited path diversity. In this paper, we present an efficient algorithm that allows routers to enable more path diversity: our algorithm let all routers compute at least the two best first hop distinct paths towards each destination and achieves a good tradeoff between path diversity and overhead. In addition, we propose a multipath routing scheme whose goal is to combine fast re-routing and load balancing loop-free routes. The low overhead of our scheme (no additional signaling messages and low complexity) and the nature of its loop-free rules allow to incrementally deploy it on current IP routers. Using actual, inferred, and generated topologies, we compare our algorithm to existing solutions.

Internet topology modeler based on map sampling

Creating a network topology is the first step in building a scenario for a network protocol simulation. The simulation results usually depend on the topology layout, especially for routing and multicasting protocols. Therefore the topology used should be generated with the highest possible accuracy. In particular, protocols designed for the Internet should be simulated over Internet-like topologies. Many topology generators currently exist but the discovery of power laws in the Internet has brought new constraints upon the generated topologies. We introduce a flexible novel way to create Internet-like topologies. It is based on an algorithm that performs a sampling on a measured Internet map. The created topologies accurately comply with the newly found power laws as well as other more common topology properties such as the average path length.

Topology Discovery at the Router Level: A New Hybrid Tool Targeting ISP Networks

For a long time, traceroute measurements combined with alias resolution methods have been the sole way to collect Internet router level maps. Recently, a new approach has been introduced with the use of a multicast management tool, mrinfo, and a recursive probing scheme. In this paper, after analyzing advantages and drawbacks of probing approaches based on traceroute and mrinfo, we propose a hybrid discovery tool, Merlin (MEasure the Router Level of the INternet), mixing mrinfo and traceroute probes. Using a central server controlling a set of distributed vantage points in order to increase the exploration coverage while limiting the probing redundancy, the purpose of Merlin is to provide an accurate router level map inside a targeted Autonomous System (AS). Merlin also takes advantage of alias resolution methods to reconnect scattered multicast components. To evaluate the performance of Merlin, we report experimental results describing its efficiency in topology exploration and reconstruction of several ASes.

Extracting intra-domain topology from mrinfo probing

Active and passive measurements for topology discovery have known an impressive growth during the last decade. If a lot of work has been done regarding inter-domain topology discovery and modeling, only a few papers raise the question of how to extract intra-domain topologies from measurements results. In this paper, based on a large dataset collected with mrinfo, a multicast tool that silently discovers all interfaces of a router, we provide a mechanism for retrieving intra-domain topologies. The main challenge is to assign an AS number to a border router whose IP addresses are not mapped to the same AS. Our algorithm is based on probabilistic and empirical IP allocation rules. The goal of our pool of rules is to converge to a consistent router to AS mapping. We show that our router-to-AS algorithm results in a mapping in more than 99% of the cases. Furthermore, with mrinfo, point-to-point links between routers can be distinguished from multiple links attached to a switch, providing an accurate view of the collected topologies. Finally, we provide a set of large intra-domain topologies in various formats.

Quantifying ases multiconnectivity using multicast information

Redundant connectivity (or multiconnectivity) between adjacent autonomous systems (ASes) is important for interdomain traffic engineering and fast recovery in case of failures. However, the redundancy of ASes business relationship links has not been quantitatively studied, mainly due to the difficulty of obtaining relevant data. In this paper, we show that the mrinfo multicast monitoring tool can provide useful data about the Internet topology and such redundant links in particular. Our analysis relies on more than four years of daily queries to about ten thousand routers mapped into more than two hundred ASes. We demonstrate that peering links between ASes are frequently redundant. In particular, our analysis shows that more than half of the studied ASes pairs are connected through multiple physical links. We then refine our analysis by considering the different types of ASes and their business relationships. A particular result of our analysis is that at least 75% of the peer-to-peer relationships between adjacent Tier-1 ASes are redundant, i.e., the connections between these ASes involve several physical links. Our analysis is conservative, providing so a lower bound, as some links might not be seen by mrinfo due to ISPs filtering policies.

Influence of Network Topology on Protocol Simulation

Simulation is one of the most widely used techniques for designing network protocols. A simulation framework provides a sandbox where a harmful design flaw can easily be detected and removed. This is done prior to implementation and experimentation in an operational environment as it is easier and cheaper to carry out. However, simulation results can be distorted if the simulation model is unrealistic. In particular the topology model used by a protocol simulation can have a great impact on the results. In this paper we present a comparison of the results of an oriented multicast protocol simulation performed on some of the major topology models currently in use in the network research community.

Graceful Convergence in Link-State IP Networks: A Lightweight Algorithm Ensuring Minimal Operational Impact

The use of real-time multimedia or mission-critical applications over IP networks puts strong pressure on service providers to operate disruption-free networks. However, after any topological change, link-state Interior Gateway Protocols (IGPs), such as IS-IS or OSPF, enter a convergence phase during which transient forwarding loops may occur. Such loops increase the network latency and cause packet losses. In this paper, we propose and evaluate an efficient algorithm aimed at avoiding such traffic disruptions without modifying these IGPs. In case of an intentional modification of the weight of a link (e.g., to shut it down for maintenance operations or to perform traffic engineering), our algorithm iteratively changes this weight, splitting the modification into a sequence of loop-free transitions. The number of weight increments that need to be applied on the link to reach its target state is minimized in order to remain usable in existing networks. Analysis performed on inferred and real Internet service provider (ISP) topologies shows that few weight increments are required to handle most link shutdown events (less than two intermediate metrics for more than 85% of the links). The evaluation of our implementation also reveals that these minimal sequences can be computed in a reasonable time.

MERLIN: MEasure the router level of the INternet

In this paper, we present a new router-level Internet mapping tool called MERLIN. MERLIN takes advantage of mrinfo, a multicast management tool that collects all IPv4 multicast enabled interfaces of a router and all its multicast links towards its neighbors. Our new probing tool fixes mrinfo technical limitations and eases the deployment of multicast probing campaign. We deploy and evaluate the performance of MERLIN at large scale. We investigate the completeness of MERLIN by providing a lower bound on the proportion of information that it may miss. We also demonstrate that the use of several vantage points is crucial to circumvent IGMP filtering in order to increase the amount of collected routers. MERLIN is a valuable tool for collecting the router-level Internet topology.

Analysis and Comparison of Internet Topology Generators

The modeling of Internet topology is of vital importance to network researchers. Some network protocols, and particularly multicast ones, have performances that depend heavily on the network topology. That is why the topology model used for the simulation of those protocols must be as realistic as possible. In particular a protocol designed for the Internet should be tested upon Internet-like generated topologies. In this paper we provide a comparative study of three topology generators. The first two are among the latest available topology generators and the third is a generator that we have created. All of them try to generate topologies that model the measured Internet topology. We check their efficiency by comparing the produced topologies with the topology of a recently collected Internet map.

Network fingerprinting: TTL-based router signatures

Fingerprinting networking equipment has many potential applications and benefits in network management and security. More generally, it is useful for the understanding of network structures and their behaviors. In this paper, we describe a simple fingerprinting mechanism based on the initial TTL values used by routers to reply to various probing messages. We show that main classes obtained using this simple mechanism are meaningful to distinguish routers platforms. Besides, it comes at a very low additional cost compared to standard active topology discovery measurements. As a proof of concept, we apply our method to gain more insight on the behavior of MPLS routers and to, thus, more accurately quantify their visible/invisible deployment.