K. Varadhan, R. Govindan, and D. Estrin. Persistent route oscillations in interdomain routing. Computer Networks (Amsterdam, Netherlands: 1999.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....are no routing loops. This example shows that our algorithm continues to work correctly even in certain badly configured systems. 9. Related Work One of the first works to report on BGP convergence problems showed that there are routing policies that cause External BGP (E BGP) to diverge [21]. Griffin and Wilfong [7] performed an analysis of E BGP convergence properties using graph theoretic methods. They showed that even checking whether an E BGP configuration can converge is an NP Complete problem. Various solutions have been proposed to address the E BGP convergence problem. ....

K. Varadhan, R. Govindan, and D. Estrin. Persistent Route Oscillations in Inter-domain Routing. Computer Networks, 32:1--16, 2000.

....it allows these policies to override distance metrics in favor of policy concerns. In contrast to pure distance vector protocols such as RIP [2] 14] BGP is not safe in the sense that routing policies can conflict in a manner that causes BGP to diverge, resulting in persistent route oscillations [21]. Moreover, the safety of BGP routing policies may not be robust with respect to network failures. Recent studies have highlighted the adverse effects of interdomain routing instability [16] 17] Although it is not known if any of the observed BGP instability has been caused by policy conflicts, ....

....A. Related Work Bertsekas et al. 1] prove convergence for a distributed version of the Bellman Ford shortest path algorithm. Because of the differences between BGP and shortest path routing mentioned above, these results do not directly apply to a protocol such as BGP. In Varadhan et al. [21], the convergence properties of an abstraction of BGP is studied. They describe a system (similar to BAD GADGET of Figure2) as an example of policies which lead to divergence. In their setting, a node must update each time it receives a new route to origin advertisement from one of its ....

[Article contains additional citation context not shown here]

K. Varadhan, R. Govindan, and D. Estrin. Persistent route oscillations in inter-domain routing. ISI technical report 96-631, USC/Information Sciences Institute, 1996.

....1.5 Mbps 2 1 Fig. 7. Policy routing example for two users with different traffic types ples, there would be a longer chain of rules) This type of oscillation in which each AS in a cycle of ASs repeatedly selects the same sequence of routers is referred to as persistent route oscillations [25]. Policy conflicts can generally be avoided by reducing manual configuration, and using routing policy registry servers or repositories. Such servers contain databases of registered domain policies. The Border Gateway Protocol (BGP) the standard inter domain routing protocol in today s ....

K. Varadhan, R. Govindan, and D. Estrin, ""persistent route oscillations in inter-domain routing"," Computer Networks, vol. 32, no. 1, pp. 1--16, January 2000.

....a motivation for information flow control. Work in firewall configuration has proposed a high level specification language that uses a high level abstraction based on formal logic [4] Our work builds heavily on the many specific BGP anomalies noted by previous work in routing instability [38], delayed convergence [24, 27] route reflector configuration [12, 32] route flap dampening [30] accidental misconfiguration [29] and the difficulties in route prediction for traffic engineering [14] The work of Griffin et al. on the Stable Paths Problem and General Stable Paths Problem is an ....

VARADHAN, K., GOVINDAN, R., AND ESTRIN, D. Persistent route oscillations in inter-domain routing. Computer Networks 32, 1 (2000), 1--16.

.... flap damping, a widely deployed mechanism on BGP routers to improve routing stability, can surprisingly exacerbate the convergence time of relatively stable routes [19] Worse of all, under unconstrained route selection condition, persistent route oscillations may occur for certain situations [16]. For such cases, routes won t be able to converge at all. Fortunately, this remains as a theoretical exercise and has not been observed in practice. 2.2.2 Convergence Model A simplified model for BGP convergence and the associated lower and upper bounds are presented in [6] This model is based ....

....ASs. BGP is not a simple shortest AS path first algorithm. The choice could be overridden by the local policies set on an AS. These policies are chosen by ASs independently so that they may lead to conflicts. In the worst case, persistent route lO oscillation will occur and route won t converge [16]. Here is an example from [16] Each AS is represented as a node and its preference function is listed in the table. Most preferred route of DO, D1, D2 are r2, r0, rl respectively, and they will never choose rl, r2, and r0 respectively. r0 rl r2 DO r0 r2 D1 r0 rl D2 r2 rl DlC( ....

[Article contains additional citation context not shown here]

K. Varadhan, R. Govindan, and D. Estrin, "Persistent Route Oscillations in Inter-Domain Routing," Computer Networks, March 2000.

....use of BGP. In particular, it is not clear how the BGP convergence in a single VPN will be impacted by the number of other VPN routes being supported over the same infrastructure. Policy interaction. BGP policies can interact in unexpected and counter intuitive ways to produce routing anomalies [24], 25] and these can even occur within a single autonomous system [26] 27] 28] 29] We need to investigate if anomalous policy conflicts can arise either within a single service provider or between providers in BGP MPLS VPNs of RFC 2547. ACKNOWLEDGMENTS Formalizing a rapidly ....

Kanan Varadhan, Ramesh Govindan, and Deborah Estrin, "Persistent route oscillations in inter-domain routing," Computer Networks, vol. 32, pp. 1--16, 2000.

....be a general mechanism for improving BGP convergence. In this paper, we present a new technique that can substantially reduce BGP convergence time. It should be noted that, because BGP allows each AS to independently formulate its routing policies, BGP might never converge on any stable routes [7], 8] In this paper we assume that any route change will eventually result in a new stable route if one exists, or result in the destination being declared unreachable. III. ASSERTIONS FOR IMPROVING ROUTING CONVERGENCE IN SIMPLE PATH VECTOR PROTOCOLS We de fi ne a route convergence period as ....

K. Varadhan, R. Govindan, and D. Estrin, "Persistent Route Oscillations in Inter-Domain Routing," Tech. Rep. 96631, SRI Network Information Center, Feb. 1996.

....or malicious routers can, among other things, force other ASes to accept bad or inefficient routes, hijack address ranges, or simply flood the network with useless route information. The security limitations of BGP are compounded by the fact that the protocol itself does not always converge [23]. Because BGP is potentially unstable at any time, it is particularly difficult to analyze. Complexity is always at odds with security. Getting the routing system to work at an acceptable level has taken huge effort in terms of designing, implementing, and deploying protocols. Moreover, as the ....

K. Varadhan, R. Govindan, and D. Estrin. Persistent Route Oscillations in Inter-Domain Routing. Computer Networks, 32(1):1--16, 2000.

....Research Projects Agency (DARPA) under contract number MDA972 99 C 0024. nentially [13] Finally, the distributed nature of the BGP algorithm makes it extremely dicult to predict its behavior. For example, researchers have discovered that some routing policy combinations can cause BGP to diverge [23]. Many surprising discoveries like this( 9] 13] 22] 21] show the unpredictability and instability of BGP. These changes made three problems of BGP more prominent. First, BGP is vulnerable to attacks from a single router. Such a concern is demonstrated to be valid by a failure [5] in which ....

K. Varadhan, R. Govindan, and D. Estrin. Persistent route oscillations in inter-domain routing. Computer Networks, 32(1):1-16, 2000.

....to post on servers or to redistribute to lists, requires prior specific permission and or a fee. SIGCOMM 02, August 19 23, 2002, Pittsburgh, Pennsylvania, USA. Copyright 2002 ACM 1 58113 570 X 02 0008 . 5.00. delayed convergence [24] persistent oscillations due to policy interactions [18, 40], and instability caused by the propagation of worms [9] In this paper we examine another source of unreliability: the misconfiguration of the routers that speak BGP. We know from numerous studies of highly reliable systems, such as aircraft, bank databases, and the telephone network, that human ....

.... deficiencies [26] In a continuation of that work they showed that convergence properties of path vector protocols such as BGP are much worse than previously assumed [24] It has also been shown that independent and uncoordinated policies in BGP can lead to persistent route oscillations [18, 40]. Most recently, the impact of Internet worms on BGP stability has been studied [9] Our study complements all of this work by analyzing the impact of another source of instability in inter domain routing: the misconfiguration of BGP speaking routers. Our study is preceded by various efforts that ....

K. Varadhan, R. Govindan, and D. Estrin. Persistent Route Oscillations in Inter-Domain Routing. Computer Networks, 32(1), 1999.

....applies local policies to select the best route for each prefix and to decide whether to advertise this route to the neighbor. Changes in these policies can trigger new advertisements. A group of ASes may have conflicting policies that lead to repeated advertising and withdrawing of routes [2, 3]. In addition, intradomain routing or topology changes may cause some routers to select new BGP routes and advertise them to neighboring ASes. BGP routing changes can cause performance problems. A single event, such as a link failure, can trigger a long sequence of updates as the routers ....

K. Varadhan, R. Govindan, and D. Estrin, "Persistent route oscillations in inter-domain routing," Tech. Rep. 96-631, USC/ISI, February 1996.

....is below the LOCAL PREF value of route r 1 . All client routers choose route r 0 because the IGP cost is lower than the IGP cost for route r 1 . IX. RELATED WORK The first work to report on BGP convergence problems showed that there are routing policies that cause External BGP (E BGP) to diverge [20]. More recently, Griffin and Wilfong [7] performed an analysis of E BGP convergence properties using graph theoretic methods. They showed that even checking whether an E BGP configuration can converge is an NPComplete problem. Various solutions have been proposed to address the E BGP convergence ....

K. Varadhan, R. Govindan, and D. Estrin. Persistent Route Oscillations in Inter-Domain Routing. Technical Report 96-631, USC/ISI, 1996.

....routes are likely to be valid for longer periods of time. In the case of RIP, a sharp real time bound for the convergence time also gives an upper bound for the life time of loops (which indeed can be created) Convergence is an even more complicated issue for BGP. Varadhan, Govindan and Estrin [52] demonstrated circumstances in which routes to a given destination persistently oscillate. The extent to which it is a practical problem for BGP on the Internet is not well understood. Grin and Wilfong [20] demonstrated that even if the BGP topology of the Internet were known, it would be ....

....the Internet topology. Villamizar et al. 53] suggest a method for route ap damping . The idea in their approach is to slow down the propagation of potentially unstable routes. While this does not eliminate route oscillations, it reduces their practical impact on performance. Varadhan et al. [52] use a formal model to derive a condition which characterizes convergent con gurations for a special class of topologies rings. Grin and Wilfong [20] described a formal model of BGP and proved that deciding convergence in that model is NP hard. In [19] Grin et al. demonstrated a condition ....

K. Varadhan, R. Govindan, and D. Estrin. Persistent route oscillations in inter-domain routing. ISI Technical Report 96-631, USC/Information Sciences Institute, 1996.

....in practice is a hard problem. BGP is designed to allow maximum flexibility in route preference policies. This makes it possible to set up a divergent BGP system while completely respecting the protocol standard. The problem of divergence is studied in several papers [3] 4] 5] 6] [7]. We will focus our attention on a different problem the length of the convergence process. While conflicting policies Or u simply rejects (uv)P , while accepting (uv)Q 0 7803 7476 2 02 17.00 (c) 2002 IEEE. v u 0 P (u v)Q Fig. 1. A dispute between u and v that would cause divergence ....

K. Varadhan, R. Govindan, and D. Estrin, "Persistent route oscillations in inter-domain routing," ISI Technical Report 96-631, USC/Information Sciences Institute, 1996.

....in practice is a hard problem. BGP is designed to allow maximum flexibility in route preference policies. This makes it possible to set up a divergent BGP system while completely respecting the protocol standard. The problem of divergence is studied in several papers [3] 4] 5] 6] [7]. We will focus our attention on a different problem the length of the convergence process. While conflicting policies that would cause divergence are theoretically possible, many practitioners claim that such policies are rarely (if ever) used in practice. However, even then, it is important to ....

K. Varadhan, R. Govindan, and D. Estrin, "Persistent route oscillations in inter-domain routing," ISI Technical Report 96-631, USC/Information Sciences Institute, 1996.

....tool for the routers made by some specific vendors. We should point out that these are limitations of any testing method for BGP, not just ours. Policies, in general, are a complex and ill understood part of the BGP protocol. For example, each AS can set its policy independently. It was shown [20] that policies which appear reasonable locally may be mutually inconsistent. Furthermore, testing whether a given set of routing policies are mutually consistent is NP hard [4] There are other difficulties with BGP testing. A design philosophy of BGP is to maintain route stability, so if the ....

K. Vardhan, R. Govindan, and D. Estrin. Persistent route oscillations in inter-domain routing. Technical Report 96-631, USC/ISI, 1996.

....as well as a window in which BGP updates with common attributes may be bundled into a single update for greater protocol efficiency. The standard recommends thirty seconds as the MinRouteAdver interval plus minus some additional random jitter. A number of recent studies, including Varadhan et al. [7] and Griffin and Wilfong [8] have explored BGP routing divergence. BGP allows the administrator of an autonomous system to specify arbitrarily complex policies. In BGP divergence, Griffin and Wilfong show that it is possible for autonomous systems to implement unsafe, or mutually unsatisfiable ....

Kannan Varadhan, Ramesh Govindan, and Deborah Estrin, "Persistent Route Oscillations in Inter-Domain Routing," Tech. Rep. USC CS TR 96631, Department of Computer Science, University of Southern California, Feb. 1996.

....as well as a window in which BGP updates with common attributes may be bundled into a single update for greater protocol eciency. The standard recommends thirty seconds as the MinRouteAdver interval plus minus some additional random jitter. A number of recent studies, including Varadhan et al. [7] and Grin and Wilfong [8] have explored BGP routing divergence. BGP allows the administrator of an autonomous system to specify arbitrarily complex policies. In BGP divergence, Grin and Wilfong show that it is possible for autonomous systems to implement unsafe, or mutually unsatis able ....

Kannan Varadhan, Ramesh Govindan, and Deborah Estrin, \Persistent Route Oscillations in Inter-Domain Routing," Tech. Rep. USC CS TR 96631, Department of Computer Science, University of Southern California, Feb. 1996.

....as well as a window in which BGP updates with common attributes may be bundled into a single update for greater protocol efficiency. The standard recommends thirty seconds as the MinRouteAdver interval plus minus some additional random jitter. A number of recent studies, including Varadhan et al. [7] and Griffin and Wilfong [8] have explored BGP routing divergence. BGP allows the administrator of an autonomous system to specify arbitrarily complex policies. In BGP divergence, Griffin and Wilfong show that it is possible for autonomous systems to implement unsafe, or mutually unsatisfiable ....

Kannan Varadhan, Ramesh Govindan, and Deborah Estrin, "Persistent Route Oscillations in Inter-Domain Routing," Tech. Rep. USC CS TR 96631, Department of Computer Science, University of Southern California, Feb. 1996.

....providers. That is, an AS does not provide transit service for its providers and peers. The interaction of locally defined routing policies can have global ramifications for the stability of the BGP system. Conflicting local policies among a collection of ASes can result in BGP route oscillations [7]. We call a collection of routing policies safe if they can never lead to BGP divergence. Verifying the safety of a set of routing policies is computationally expensive [8] and would require ASes to reveal their (often proprietary) routing policies. Safety is not guaranteed even if each AS ....

K. Varadhan, R. Govindan, and D. Estrin, "Persistent route oscillations in inter-domain routing," Tech. Rep. 96-631, USC/ISI, February 1996.

....and pathological. In a subsequent paper [13] they identi ed reasons behind many of those unexpected routing messages and described remedies for them. Labovitz et al. 11, 12] have also shown that signi cant correlation exists between network usage and instability observed for BGP. Varadhan et al. [21] showed that there are routing policies that can cause BGP routes to oscillate and never converge to a stable con guration. Govindan et al. 6] subsequently described an architecture for coordinating routing policies and avoiding routing instabilities that can arise due to con icting poli cies. ....

K. Varadhan, R. Govindan, and D. Estrin. Persistent Route Oscillations in Inter{Domain Routing. ISI technical report 96-631, USC/Information Sciences Institute, 1996.

....interdomain routing protocol employed on the Internet. As required of any interdomain protocol, BGP allows policy based metrics to override distance based metrics and enables each autonomous system to independently define its routing policies with little or no global coordination. Varadhan et al. [11] have shown that there are collections of routing policies that together are not safe in the sense that they can cause BGP to diverge. That is, an unsafe collection of routing policies can result in some autonomous systems exchanging BGP routing messages indefinitely, without ever converging to a ....

....is strictly larger. 1 Introduction BGP [9, 7, 10] allows each autonomous system to independently formulate its routing policies, and it allows these policies to override distance metrics in favor of policy concerns. In contrast to pure distance vector protocols such as RIP [8] Varadhan et al. [11] have shown that there are routing policies that are unsafe in the sense that they can cause BGP to diverge. Although it seems that BGP divergence has not yet occurred in practice, it could potentially introduce a great deal of instability into the global routing system. The goal of this paper is ....

[Article contains additional citation context not shown here]

K. Varadhan, R. Govindan, and D. Estrin. Persistent route oscillations in inter-domain routing. ISI technical report 96631, USC/Information Sciences Institute, 1996.

....result of a similar bound for path vector algorithms. The adoption of the path vector is widely and incorrectly believed to provide BGP with significantly improved convergence properties over traditional DV protocols, including RIP [12] A number of recent studies, including Varadhan et al. [23] and Griffin and Wilfong [8] have explored BGP routing divergence. As we describe in the next Section, BGP allows the administrator of an autonomous system to specify arbitrarily complex policies. In BGP divergence, Griffin and Wilfong show that it is possible for autonomous systems to implement ....

K. Varadhan, R. Govindan, and D. Estrin. Persistent Route Oscillations in Inter-Domain Routing. Technical Report USC CS TR 96-631, Department of Computer Science, University of Southern California, Feb. 1996.

....community, there have been two threads of prior research into the following properties of BGP: stability and convergence delays. Stability: The first thread started with the observation that there existed certain policy configurations which could cause persistent route oscillations in BGP [19]. Later, Griffin and Wilfong [6] showed the intractability of determining a safe policy configuration for BGP. Finally, Rexford and Gao [20] proved that if BGP s policy expressiveness is confined to a simple set of policies, persistent route oscillations cannot occur. Independently, Labovitz et ....

K. Varadhan, R. Govindan, and D. Estrin, "Persistent Route Oscillations in Inter-Domain Routing," Computer Networks, March 2000.

No context found.

K. Varadhan, R. Govindan, and D. Estrin. Persistent route oscillations in interdomain routing. Computer Networks (Amsterdam, Netherlands: 1999.

No context found.

K. Varadhan, R. Govindan, D. Estrin, "Persistent Route Oscillations in Inter-Domain Routing", in Computer Networks, Mar 2000.

No context found.

K. Varadhan, et al. Persistent route oscillations in inter-domain routing. Computer Networks, Vol.32(No.1):1--16, 2000.

No context found.

K. Varadhan, R. Govindan, and D. Estrin. Persistent Route Oscillations in Inter-Domain Routing. Computer Networks, March 2000.

No context found.

Kannan Varadhan, Ramesh Govindan, and Deborah Estrin. Persistent route oscillations in inter-domain routing. Computer Networks (Amsterdam, Netherlands: 1999.

No context found.

K. Varadhan, R. Govindan, and D. Estrin. Persistent Route Oscillations in Inter-domain Routing. Computer Networks, 32:1--16, 2000.

No context found.

K. Varadhan, R. Govindan, and D. Estrin. Persistent route oscillations in inter-domain routing. ISI technical report 96-631, USC/Information Sciences Institute, 1996.

No context found.

K. Varadhan, R. Govindan, and D. Estrin. Persistent route oscillations in interdomain routing. Computer Networks (Amsterdam, Netherlands: 1999.

No context found.

Kannan Varadhan, Ramesh Govindan, and Deborah Estrin. Persistent route oscillations in inter-domain routing. Computer Networks, 32(1):1--16, 1999.

No context found.

Varadhan, K., R. Govindan, and D. Estrin, "Persistent Route Oscillations in Inter-domain Routing, "Tech. Rep. 96-631, USC/ISI, February, 1996.

No context found.

K. Varadhan, R. Govindan, and D. Estrin. Persistent Route Oscillations in Interdomain Routing. Computer Networks, 32:1--16, 2000. 4

No context found.

K. Varadhan, R. Govindan, and D. Estrin. Persistent Route Oscillations in Inter-domain Routing. Computer Networks, 32:1--16, 2000.

No context found.

K. Varadhan, R. Govindan, and D. Estrin. Persistent Route Oscillations in Inter-domain Routing. Computer Networks, 32:1--16, 2000.

No context found.

K. Varadhan, R. Govindan, and D. Estrin. "Persistent Route Oscillations in Inter-Domain Routing ". Computer Networks, 32:1-16, 2000.

No context found.

K. Varadhan, R. Govindan, and D. Estrin. Persistent Route Oscillations in Inter-Domain Routing. Computer Networks, 32(1):1--16, 2000.

No context found.

VARADHAN, K., GOVINDAN, R., AND ESTRIN, D. Persistent route oscillations in inter-domain routing. Computer Networks 32,1 (2000), 1--16.

No context found.

K. Varadhan, R. Govindan, and D. Estrin. "Persistent Route Oscillations in Inter-Domain Routing ". Computer Networks, 32:1-16, 2000.

No context found.

Kannan Varadhan, Ramesh Govindan, and Deborah Estrin. Persistent route oscillations in inter-domain routing. Computer Networks, 32(1):1-16, January 2000.

No context found.

Kannan Varadhan, Ramesh Govindan, and Deborah Estrin. Persistent Route Oscillations in Inter-Domain Routing. Technical Report CS-TR-96-631, University of Southern California, March 1996.

No context found.

Kannan Varadhan, Ramesh Govindan, and Deborah Estrin. Persistent route oscillations in interdomain routing. Computer Networks, 32(1):1--16, 2000.

No context found.

K. Varadhan, R. Govindan, and D. Estrin. Persistent Route Oscillations in Inter-Domain Routing. Computer Networks, March 2000.

No context found.

Kannan Varadhan, Ramesh Govindan, and Deborah Estrin. Persistent Route Oscillations in Inter-Domain Routing. Technical Report 96-631, USC/Information Sciences Institute, March 1996.

No context found.

K. Varadhan, R. Govindan, and D. Estrin. Persistent route oscillations in inter-domain routing. Computer Networks, 32(1):1--16, 2000.

No context found.

K. Varadhan, R. Govindan, and D. Estrin, "Persistent Route Oscillations in Inter-Domain Routing," Tech. Rep. 96631, SRI Network Information Center, Feb. 1996.

No context found.

K. Varadhan, R. Govindan, and D. Estrin, \Persistent route oscillations in inter-domain routing," Tech. Rep. 96-631, USC/ISI, February 1996.

No context found.

K. Varadhan, R. Govindan, and D. Estrin, \Persistent route oscillations in inter-domain routing," Tech. Rep. 96-631, USC/ISI, February 1996.

First 50 documents  Next 50

Online articles have much greater impact   More about CiteSeer.IST   Add search form to your site   Submit documents   Feedback  

CiteSeer.IST - Copyright Penn State and NEC