AS-Path Prepending: There is no rose without a thorn

Inbound traffic engineering (ITE) - -the process of announcing routes to, e.g., maximize revenue or minimize congestion - -is an essential task for Autonomous Systems (ASes). AS Path Prepending (ASPP) is an easy to use and well-known ITE technique that routing manuals show as one of the first alternatives to influence other ASes' routing decisions. We observe that origin ASes currently prepend more than 25% of all IPv4 prefixes. ASPP consists of inflating the BGP AS path. Since the length of the AS path is the second tie-breaker in the BGP best path selection, ASPP can steer traffic to other routes. Despite being simple and easy to use, the appreciation of ASPP among operators and researchers is diverse. Some have questioned its need, effectiveness, and predictability, as well as voiced security concerns. Motivated by these mixed views, we revisit ASPP. Our longitudinal study shows that ASes widely deploy ASPP, and its utilization has slightly increased despite public statements against it. We surprisingly spot roughly 6k ASes originating at least one prefix with prepends that achieve no ITE goal. With active measurements, we show that ASPP effectiveness as an ITE tool depends on the AS location and the number of available upstreams; that ASPP security implications are practical; identify that more than 18% of the prepended prefixes contain unnecessary prepends that achieve no apparent goal other than amplifying existing routing security risks. We validate our findings in interviews with 20 network operators

A BGP SOLVER FOR HOT-POTATO ROUTING SENSITIVITY ANALYSIS

Abstract The interactions between the IGP and BGP routing protocols which are running inside an ISP’s network are sometimes hard to understand. The problem becomes particularly complex when there are dozens of routers/links and several thousands of destination prefixes. In this paper, we present a publicly available routing solver to evaluate routing what-if scenarios. The solver is able to model the complete network of an ISP and given the external routes learned by this ISP, to compute the paths towards all the destination prefixes. We demonstrate the use of our routing solver, C-BGP, by showing the results of an analysis of the link/router failure sensitivity in a transit network. Based on the analysis’ results, we can pinpoint links/routers whose failure has an important impact on the selection of BGP routes. The deployment of protection techniques that are used for optical links, SONET-SDH and MPLS should be considered for these links/routers

A BGP Solver for Hot-Potato Routing Sensitivity Analysis

The interactions between the IGP and BGP routing protocols which are running inside an ISP's network are sometimes hard to understand. The problem becomes particularly complex when there are dozens of routers/links and several thousands of destination prefixes. In this paper, we present a publicly available routing solver to evaluate routing what-if scenarios. The solver is able to model the complete network of an ISP and given the external routes learned by this ISP, to compute the paths towards all the destination prefixes. We demonstrate the use of our routing solver, C-BGP, by showing the results of an analysis of the link/router failure sensitivity in a transit network. Based on the analysis' results, we can pinpoint links/routers whose failure has an important impact on the selection of BGP routes. The deployment of protection techniques that are used for optical links, SONET-SDH and MPLS should be considered for these links/routers. Keywords---Interdomain routing, BGP, network design

A BGP Solver for Hot-Potato Routing Sensitivity Analysis

The interactions between the IGP and BGP routing protocols which are running inside an ISP's network are sometimes hard to understand. The problem becomes particularly complex when there are dozens of routers/links and several thousands of destination prefixes. In this paper, we present a publicly available routing solver to evaluate routing what-if scenarios. The solver is able to model the complete network of an ISP and given the external routes learned by this ISP, to compute the paths towards all the destination prefixes. We demonstrate the use of our routing solver, C-BGP, by showing the results of an analysis of the link/router failure sensitivity in a transit network. Based on the analysis' results, we can pinpoint links/routers whose failure has an important impact on the selection of BGP routes. The deployment of protection techniques that are used for optical links, SONET-SDH and MPLS should be considered for these links/routers