Configuration changes are a common source of instability in networks, leading to outages, performance disruptions, and security vulnerabilities. Even when the initial and final configurations are correct, the update process itself often steps through intermediate configurations that exhibit incorrect behaviors. This paper introduces the notion of consistent network updates---updates that are guaranteed to preserve well-defined behaviors when transitioning mbetween configurations. We identify two distinct consistency levels, per-packet and per-flow, and we present general mechanisms for implementing them in Software-Defined Networks using switch APIs like OpenFlow. We develop a formal model of OpenFlow networks, and prove that consistent updates preserve a large class of properties. We describe our prototype implementation, including several optimizations that reduce the overhead required to perform consistent updates. We present a verification tool that leverages consistent updates to significantly reduce the complexity of checking the correctness of network control software. Finally, we describe the results of some simple experiments demonstrating the effectiveness of these optimizations on example applications.

/pdf/abstractions-for-network-update-3dox41dgf6.pdf

Abstractions for network update

A wireless telecommunication system comprises base stations for communicating with terminal devices. One or more base stations support a power boost operating mode in which a base station's available transmission power is concentrated in a subset of its available transmission resources to provide enhanced transmission powers as compared to transmission powers on these transmission resources when the base station is not operating in the power boost mode. A base station establishes an extent to which one or more base stations in the wireless telecommunications system support the power boost operating mode conveys an indication of this to a terminal device. The terminal device receives the indication and uses the corresponding information to control its acquisition of a base station of the wireless telecommunication system, for example by taking account of which base stations support power boosting and/or when power boosting is supported during a cell attach procedure.

Telecommunications apparatus and methods

The complexity of network management is widely recognized as one of the biggest challenges facing the Internet today. Point solutions for individual problems further increase system complexity while not addressing the underlying causes. In this paper, we argue that many network-management problems stem from the same root cause---the need to maintain consistency between the physical and logical configuration of the routers. Hence, we propose VROOM (Virtual ROuters On the Move), a new network-management primitive that avoids unnecessary changes to the logical topology by allowing (virtual) routers to freely move from one physical node to another. In addition to simplifying existing network-management tasks like planned maintenance and service deployment, VROOM can also help tackle emerging challenges such as reducing energy consumption. We present the design, implementation, and evaluation of novel migration techniques for virtual routers with either hardware or software data planes. Our evaluation shows that VROOM is transparent to routing protocols and results in no performance impact on the data traffic when a hardware-based data plane is used.

/pdf/virtual-routers-on-the-move-live-router-migration-as-a-3icw5y7mpg.pdf

Virtual routers on the move: live router migration as a network-management primitive

We present Dionysus, a system for fast, consistent network updates in software-defined networks. Dionysus encodes as a graph the consistency-related dependencies among updates at individual switches, and it then dynamically schedules these updates based on runtime differences in the update speeds of different switches. This dynamic scheduling is the key to its speed; prior update methods are slow because they pre-determine a schedule, which does not adapt to runtime conditions. Testbed experiments and data-driven simulations show that Dionysus improves the median update speed by 53--88% in both wide area and data center networks compared to prior methods.

/pdf/dynamic-scheduling-of-network-updates-1fmucv9mvs.pdf

Dynamic scheduling of network updates

Datacenter networks (DCNs) are constantly evolving due to various updates such as switch upgrades and VM migrations. Each update must be carefully planned and executed in order to avoid disrupting many of the mission-critical, interactive applications hosted in DCNs. The key challenge arises from the inherent difficulty in synchronizing the changes to many devices, which may result in unforeseen transient link load spikes or even congestions. We present one primitive, zUpdate, to perform congestion-free network updates under asynchronous switch and traffic matrix changes. We formulate the update problem using a network model and apply our model to a variety of representative update scenarios in DCNs. We develop novel techniques to handle several practical challenges in realizing zUpdate as well as implement the zUpdate prototype on OpenFlow switches and deploy it on a testbed that resembles real DCN topology. Our results, from both real-world experiments and large-scale trace-driven simulations, show that zUpdate can effectively perform congestion-free updates in production DCNs.

http://conferences.sigcomm.org/sigcomm/2013/papers/sigcomm/p411.pdf

zUpdate: updating data center networks with zero loss

Segment Routing (SR) leverages the source routing paradigm. A node
steers a packet through an ordered list of instructions, called
segments. A segment can represent any instruction, topological or
service-based. A segment can have a semantic local to an SR node or
global within an SR domain. SR allows to enforce a flow through any
topological path while maintaining per-flow state only at the ingress
nodes to the SR domain. Segment Routing can be directly applied to the
MPLS architecture with no change on the forwarding plane. A segment is
encoded as an MPLS label. An ordered list of segments is encoded as a
stack of labels. The segment to process is on the top of the stack.
Upon completion of a segment, the related label is popped from the
stack. Segment Routing can be applied to the IPv6 architecture, with a
new type of routing header. A segment is encoded as an IPv6 address.
An ordered list of segments is encoded as an ordered list of IPv6
addresses in the routing header. The active segment is indicated by
the Destination Address of the packet. The next active segment is
indicated by a pointer in the new routing header.

Segment Routing Architecture

Segment Routing (SR) leverages the source routing paradigm. A node
steers a packet through a controlled set of instructions, called
segments, by prepending the packet with an SR header. In the MPLS
dataplane, the SR header is instantiated through a label stack. This
document specifies the forwarding behavior to allow instantiating SR
over the MPLS dataplane.

Segment Routing with the MPLS Data Plane

This paper presents a solution aimed at avoiding losses of connectivity when an eBGP peering link is shut down by an operator for a maintenance. Currently, shutting down an eBGP session can lead to transient losses of connectivity even though alternate path are available at the borders of the network. This is very unfortunate as ISPs face more and more stringent service level agreements, and maintenance operations are predictable operations, so that there is time to adapt to the change and preserve the respect of the service level agreement.

/pdf/avoiding-disruptions-during-maintenance-operations-on-bgp-3nl83mazur.pdf

Avoiding disruptions during maintenance operations on BGP sessions

This document presents Topology Independent Loop-free Alternate Fast
Re-route (TI-LFA), aimed at providing protection of node and adjacency
segments within the Segment Routing (SR) framework. This Fast Re-route
(FRR) behavior builds on proven IP-FRR concepts being LFAs, remote
LFAs (RLFA), and remote LFAs with directed forwarding (DLFA). It
extends these concepts to provide guaranteed coverage in any IGP
network. A key aspect of TI-LFA is the FRR path selection approach
establishing protection over the expected post-convergence paths from
the point of local repair, dramatically reducing the operational need
to control the tie-breaks among various FRR options.

Topology Independent Fast Reroute using Segment Routing

Segment Routing (SR) allows for a flexible definition of end-to-end
paths within IGP topologies by encoding paths as sequences of
topological sub-paths, called "segments". These segments are
advertised by the link-state routing protocols (IS-IS and OSPF). This
draft describes the necessary IS-IS extensions that need to be
introduced for Segment Routing operating on an MPLS data-plane.

Bruno Decraene

Papers

Segment Routing Architecture

Segment Routing with the MPLS Data Plane

Avoiding disruptions during maintenance operations on BGP sessions

Topology Independent Fast Reroute using Segment Routing

IS-IS Extensions for Segment Routing