Efficient Synthesis of Network Updates

Software-defined networking (SDN) is revolutionizing the networking industry, but current SDN programming platforms do not provide automated mechanisms for updating global configurations on the fly. Implementing updates by hand is challenging for SDN programmers because networks are distributed systems with hundreds or thousands of interacting nodes. Even if initial and final configurations are correct, naively updating individual nodes can lead to incorrect transient behaviors, including loops, black holes, and access control violations. This paper presents an approach for automatically synthesizing updates that are guaranteed to preserve specified properties. We formalize network updates as a distributed programming problem and develop a synthesis algorithm based on counterexample-guided search and incremental model checking. We describe a prototype implementation, and present results from experiments on real-world topologies and properties demonstrating that our tool scales to updates involving over one-thousand nodes

Automated Formal Analysis of Internet Routing Configurations

Today\u27s Internet interdomain routing protocol, the Border Gateway Protocol (BGP), is increasingly complicated and fragile due to policy misconfigurations by individual autonomous systems (ASes). To create provably correct networks, the past twenty years have witnessed, among many other efforts, advances in formal network modeling, system verification and testing, and point solutions for network management by formal reasoning. On the conceptual side, the formal models usually abstract away low-level details, specifying what are the correct functionalities but not how to achieve them. On the practical side, system verification of existing networked systems is generally hard, and system testing or simulation provide limited formal guarantees. This is known as a long standing challenge in network practice --- formal reasoning is decoupled from actual implementation. This thesis seeks to bridge formal reasoning and actual network implementation in the setting of the Border Gateway Protocol (BGP), by developing the Formally Verifiable Routing (FVR) toolkit that combines formal methods and programming language techniques. Starting from the formal model, FVR automates verification of routing models and the synthesis of faithful implementations that carries the correctness property. Conversely, starting from large real-world BGP systems with arbitrary policy configurations, automates the analysis of Internet routing configurations, and also includes a novel network reduction technique that scales up existing techniques for automated analysis. By developing the above formal theories and tools, this thesis aims to help network operators to create and manage BGP systems with correctness guarantee

Optimal route reflection topology design

An Autonomous System (AS) is a group of Internet Protocol-based networks with a single and clearly defined external routing policy, usually under single ownership, trust or administrative control. The AS represents a connected group of one or more blocks of IP addresses, called IP prefixes, that have been assigned to that organization and provides a single routing policy to systems outside the AS. The Internet is composed of the interconnection of several thousands of ASes, which use the Border Gateway Protocol (BGP) to exchange network prefixes (aggregations of IP addresses) reachability advertisements. BGP advertisements (or updates) are sent over BGP sessions administratively set between pairs of routers. BGP is a path vector routing protocol and is used to span different ASes. A path vector protocol defines a route as a pairing between a destination and the attributes of the path to that destination. Interior Border Gateway Protocol (iBGP) refers to the BGP neighbor relationship within the same AS. When BGP neighbor relationship are formed between two peers belonging to different AS are called Exterior Border Gateway Protocol (eBGP). In the last case, BGP routers are called Autonomous System Border Routers (ASBRs), while those running only iBGP sessions are referred to as Internal Routers (IRs). Traditional iBGP implementations require a full-mesh of sessions among routers of each AS

Improving end-to-end availability using overlay networks

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2005.Includes bibliographical references (p. 139-150).The end-to-end availability of Internet services is between two and three orders of magnitude worse than other important engineered systems, including the US airline system, the 911 emergency response system, and the US public telephone system. This dissertation explores three systems designed to mask Internet failures, and, through a study of three years of data collected on a 31-site testbed, why these failures happen and how effectively they can be masked. A core aspect of many of the failures that interrupt end-to-end communication is that they fall outside the expected domain of well-behaved network failures. Many traditional techniques cope with link and router failures; as a result, the remaining failures are those caused by software and hardware bugs, misconfiguration, malice, or the inability of current routing systems to cope with persistent congestion.The effects of these failures are exacerbated because Internet services depend upon the proper functioning of many components-wide-area routing, access links, the domain name system, and the servers themselves-and a failure in any of them can prove disastrous to the proper functioning of the service. This dissertation describes three complementary systems to increase Internet availability in the face of such failures. Each system builds upon the idea of an overlay network, a network created dynamically between a group of cooperating Internet hosts. The first two systems, Resilient Overlay Networks (RON) and Multi-homed Overlay Networks (MONET) determine whether the Internet path between two hosts is working on an end-to-end basis. Both systems exploit the considerable redundancy available in the underlying Internet to find failure-disjoint paths between nodes, and forward traffic along a working path. RON is able to avoid 50% of the Internet outages that interrupt communication between a small group of communicating nodes.MONET is more aggressive, combining an overlay network of Web proxies with explicitly engineered redundant links to the Internet to also mask client access link failures. Eighteen months of measurements from a six-site deployment of MONET show that it increases a client's ability to access working Web sites by nearly an order of magnitude. Where RON and MONET combat accidental failures, the Mayday system guards against denial- of-service attacks by surrounding a vulnerable Internet server with a ring of filtering routers. Mayday then uses a set of overlay nodes to act as mediators between the service and its clients, permitting only properly authenticated traffic to reach the server.by David Godbe Andersen.Ph.D