Beichuan Zhang

Named data networking

Named Data Networking (NDN) is one of five projects funded by the U.S. National Science Foundation under its Future Internet Architecture Program. NDN has its roots in an earlier project, Content-Centric Networking (CCN), which Van Jacobson first publicly presented in 2006. The NDN project investigates Jacobsons proposed evolution from todays host-centric network architecture (IP) to a data-centric network architecture (NDN). This conceptually simple shift has far-reaching implications for how we design, develop, deploy, and use networks and applications. We describe the motivation and vision of this new architecture, and its basic components and operations. We also provide a snapshot of its current design, development status, and research challenges. More information about the project, including prototype implementations, publications, and annual reports, is available on named-data.net.

NLSR: named-data link state routing protocol

This paper presents the design of the Named-data Link State Routing protocol (NLSR), a routing protocol for Named Data Networking (NDN). Since NDN uses names to identify and retrieve data, NLSR propagates reachability to name prefixes instead of IP prefixes. Moreover, NLSR differs from IP-based link-state routing protocols in two fundamental ways. First, NLSR uses Interest/Data packets to disseminate routing updates, directly benefiting from NDNs data authenticity. Second, NLSR produces a list of ranked forwarding options for each name prefix to facilitate NDNs adaptive forwarding strategies. In this paper we discuss NLSRs main design choices on (1) a hierarchical naming scheme for routers, keys, and routing updates, (2) a hierarchical trust model for routing within a single administrative domain, (3) a hop-by-hop synchronization protocol to replace the traditional network-wide flooding for routing update dissemination, and (4) a simple way to rank multiple forwarding options. Compared with IP-based link state routing, NLSR offers more efficient update dissemination, built-in update authentication, and native support of multipath forwarding.

Observing the evolution of internet as topology

Characterizing the evolution of Internet topology is important to our understanding of the Internet architecture and its interplay with technical, economic and social forces. A major challenge in obtaining empirical data on topology evolution is to identify real topology changes from the observed topology changes, since the latter can be due to either topology changes or transient routing dynamics. In this paper, we formulate the topology liveness problem and propose a solution based on the analysis of BGP data. We find that the impact of transient routing dynamics on topology observation decreases exponentially over time, and that the real topology dynamics consist of a constant-rate birth process and a constant-rate death process. Our model enables us to infer real topology changes from observation data with a given confidence level. We demonstrate the usefulness of the model by applying it to three applications: providing more accurate views of the topology, evaluating theoretical evolution models, and empirically characterizing the trends of topology evolution. We find that customer networks and provider networks have distinct evolution trends, which can provide an important input to the design of future Internet routing architecture.

The (in)completeness of the observed internet AS-level structure

Despite significant efforts to obtain an accurate picture of the Internets connectivity structure at the level of individual autonomous systems (ASes), much has remained unknown in terms of the quality of the inferred AS maps that have been widely used by the research community. In this paper, we assess the quality of the inferred Internet maps through case studies of a sample set of ASes. These case studies allow us to establish the ground truth of connectivity between this set of ASes and their directly connected neighbors. A direct comparison between the ground truth and inferred topology maps yield insights into questions such as which parts of the actual topology are adequately captured by the inferred maps, which parts are missing and why, and what is the percentage of missing links in these parts. This information is critical in assessing, for each class of real-world networking problems, whether the use of currently inferred AS maps or proposed AS topology models is, or is not, appropriate. More importantly, our newly gained insights also point to new directions towards building realistic and economically viable Internet topology maps.

In search of the elusive ground truth: the internet's as-level connectivity structure

Despite significant efforts to obtain an accurate picture of the Internets actual connectivity structure at the level of individual autonomous systems (ASes), much has remained unknown in terms of the quality of the inferred AS maps that have been widely used by the research community. In this paper we assess the quality of the inferred Internet maps through case studies of a set of ASes. These case studies allow us to establish the ground truth of AS-level Internet connectivity between the set of ASes and their directly connected neighbors. They also enable a direct comparison between the ground truth and inferred topology maps and yield new insights into questions such as which parts of the actual topology are adequately captured by the inferred maps, and which parts are missing and why. This information is critical in assessing for what kinds of real-world networking problems the use of currently inferred AS maps or proposed AS topology models are, or are not, appropriate. More importantly, our newly gained insights also point to new directions towards building realistic and economically viable Internet topology maps.

IPv4 address allocation and the BGP routing table evolution

The IP address consumption and the global routing table size are two of the vital parameters of the Internet growth. In this paper we quantitatively characterize the IPv4 address allocations made over the past six years and the global BGP routing table size changes during the same period of time. About 63,000 address blocks have been allocated since the beginning of the Internet, of which about 18,000 address blocks were allocated during our study period, from November 1997 to August 2004. Among these 18,000 allocations, 90% of them started being announced into the BGP routing table within 75 days after the allocation, while 8% of them has not been used up to now. Among all the address blocks that have ever been used, 45% of them were split into fragments smaller than the original allocated blocks; without these fragementations, the current BGP table would have been about half of its current size. Furthermore, we found that the evolution of BGP routing table consists of both the appearance of new prefixes and the disappearance of old prefixes. While the change of the BGP routing table size only reflects the combined results of the two processes, the dynamics of either process is much higher than that of the BGP table size. Finally, we classify routing prefixes into covering and covered ones, and examine their evolution separately. For the covered prefixes, which account for almost half of the BGP table size, we infer their practical motives such as multihoming, load balancing, and traffic engineering, etc., via a classification method.

On the Aggregatability of Router Forwarding Tables

The rapid growth of global routing tables has raised concerns among many Internet Service Providers. The most immediate concern regarding routing scalability is the size of the Forwarding Information Base (FIB), which seems to be growing at a faster pace than router hardware can support. This paper focuses on one potential solution to this problem - FIB aggregation, i.e., aggregating FIB entries without affecting the forwarding paths taken by data traffic. Compared with alternative solutions to the routing scalability problem, FIB aggregation is particularly appealing because it is a purely local software optimization limited within a router, requiring no changes to routing protocols or router hardware. To understand the feasibility of using FIB aggregation to extend router lifetime, we present several FIB aggregation algorithms and evaluate their performance using routing tables and updates from tens of networks. We find that FIB aggregation can reduce the FIB table size by as much as 70% with small computational overhead. We also show that the computational overhead can be controlled through various mechanisms.

Identifying BGP routing table transfers

BGP routing updates collected by monitoring projects such as RouteViews and RIPE have been a vital source to our understanding of the global routing system. The updates logged by these monitoring projects are generated either by individual route changes, or are part of BGP table transfer. In particular, a session reset between a monitoring station and its BGP peers can result in the peer sending its entire BGP routing table to the monitoring station. In this paper, we present a Minimum Collection Time (MCT) algorithm that accurately identify the start and duration of routing table transfers. Using three months of data from 14 different peers, MCT can identify routing table transfers triggered by BGP session resets with 100% accuracy, and can pinpoint the exact starting time of table transfers in 90% of the cases.

On the role of routing in named data networking

A unique feature of Named Data Networking (NDN) is that its forwarding plane can detect and recover from network faults on its own, enabling each NDN router to handle network failures locally without relying on global routing convergence. This new feature prompts us to re-examine the role of routing in an NDN network: does it still need a routing protocol? If so, what impact may an intelligent forwarding plane have on the design and operation of NDN routing protocols? Through analysis and extensive simulations, we show that routing protocols remain highly beneficial in an NDN network. Routing disseminates initial topology and policy information as well as long-term changes in them, and computes the routing table to guide the forwarding process. However, because the forwarding plane is capable of detecting and recovering from failures quickly, routing no longer needs to handle short-term churns in the network. Freeing routing protocols from short-term churns can greatly improve their scalability and stability, enabling NDN to use routing protocols that were previously viewed as unsuitable for real networks.

Analysis of BGP Update Surge during Slammer Worm Attack

Although the Internet routing infrastructure was not a direct target of the January 2003 Slammer worm attack, the worm attack coincided in time with a large, globally observed increase in the number of BGP routing update messages. Our analysis shows that the current global routing protocol BGP allows local connectivity dynamics to propagate globally. As a result, any small number of edge networks can potentially cause wide-scale routing overload. For example, two small edges ASes, which announced less than 0.25% of BGP routing table entries, contributed over 6% of total update messages observed at monitoring points during the worm attack. Although BGP route flap damping has been proposed to eliminate such undesirable global consequences of edge instability, our analysis shows that damping has not been fully deployed even within the Internet core. Our simulation further reveals that partial deployment of BGP damping not only has limited effect, but may also worsen the routing performance under certain topological conditions. The results show that it remains a research challenge to design a routing protocol that can prevent local dynamics from triggering global messages in order to scale well in a large, dynamic environment.