IP anycast, with its innate ability to find nearby resources in a robust and efficient fashion, has long been considered an important means of service discovery. The growth of P2P applications presents appealing new uses for IP anycast. Unfortunately, IP anycast suffers from serious problems: it is very hard to deploy globally, it scales poorly by the number of anycast groups, and it lacks important features like load-balancing. As a result, its use is limited to a few critical infrastructure services such as DNS root servers. The primary contribution of this paper is a new IP anycast architecture, PIAS, that overcomes these problems while largely maintaining the strengths of IP anycast. PIAS makes use of a proxy overlay that advertises IP anycast addresses on behalf of group members and tunnels anycast packets to those members. The paper presents a detailed design of PIAS and evaluates its scalability and efficiency through simulation. We also present preliminary measurement results on anycasted DNS root servers that suggest that IP anycast provides good affinity. Finally, we describe how PIAS supports two important P2P and overlay applications.

/pdf/towards-a-global-ip-anycast-service-2xr1pr4z64.pdf

Towards a global IP anycast service

Several recently proposed multicast protocols use in-packet Bloom filters to encode multicast trees. These mechanisms are in principle highly scalable because no per-flow state is required in the routers and because routing decisions can be made efficiently by simply checking for the presence of outbound links in the filter. Yet, the viability of previous approaches is limited by the possibility of forwarding anomalies caused by false positives inherent in Bloom filters. This paper explores such anomalies, namely (1) packets storms, (2) forwarding loops and (3) flow duplication. We propose stateless solutions that increase the robustness and the scalability of Bloom filter-based multicast protocols. In particular, we show that the parameters of the filter need to be varied to guarantee the stability of the packet forwarding, and we present a bit permutation technique that effectively prevents both accidental and maliciously created anomalies. We evaluate our solutions in the context of BloomCast, a source-specific inter-domain multicast protocol, using analytical methods and simulations.

/pdf/forwarding-anomalies-in-bloom-filter-based-multicast-3sfubzu0lj.pdf

Forwarding anomalies in Bloom filter-based multicast

Despite its growing use in critical infrastructure services, the performance of IP(v4) Anycast and its interaction with IP routing practices is not well understood. In this paper, we present the results of a detailed measurement study of IP Anycast. Our study uses a two-pronged approach. First, using a variant of known latency estimation techniques, we measure the performance of current commercially operational IP Anycast deployments from a large number (>20,000) of vantage points. Second, we deploy our own small-scale anycast service that allows us to perform controlled tests under different deployment and failure scenarios. To the best of our knowledge, our study represents the first large-scale evaluation of existing anycast services and the first evaluation of the behavior of IP Anycast under failure.We find that: (1) IP Anycast, if deployed in an ad-hoc manner, does not offer good latency-based proximity, (2) IP Anycast, if deployed in an ad-hoc manner, does not provide fast failover to clients, (3) IP Anycast typically offers good affinity to all clients with the exception of those that explicitly load balance traffic across multiple providers, (4) IP Anycast, by itself, is not effective in balancing client load across multiple sites. We thus propose and evaluate practical means by which anycast deployments can achieve good proximity, fast failover and control over the distribution of client load. Overall, our results suggest that an IP Anycast service, if deployed carefully, can offer good proximity, load balance, and failover behavior.

/pdf/a-measurement-based-deployment-proposal-for-ip-anycast-2mb4iz6otf.pdf

A measurement-based deployment proposal for IP anycast

This memo defines an address allocation policy in which the address of
the Rendezvous Point (RP) is encoded in an IPv6 multicast group
address. For Protocol Independent Multicast - Sparse Mode (PIM-SM),
this can be seen as a specification of a group-to-RP mapping
mechanism. This allows an easy deployment of scalable inter-domain
multicast and simplifies the intra-domain multicast configuration as
well. This memo updates the addressing format presented in RFC 3306.
[STANDARDS-TRACK]

/pdf/embedding-the-rendezvous-point-rp-address-in-an-ipv6-559t0nhg8s.pdf

Embedding the Rendezvous Point (RP) Address in an IPv6 Multicast Address

Existing anycast routing protocols solely route packets to the closest group member. In this paper, we introduce density-based anycast routing, a new anycast routing strategy particularly suitable for unstable networks. Instead of routing packets merely on proximity information to the closest member, density-based anycast routing considers the number of available anycast group members for its routing decision. To evaluate the benefits of densitybased routing, we present a unified model to analyze pure proximitybased, pure density-based, as well as combined routing strategies. With an extensive simulation study, we then evaluate these strategies in multiple mobile scenarios. The two main results are that (i) density-based routing increases the probability of successful packet delivery when the network is unstable; and (ii) for particular mobile scenarios, density-based routing finds even shorter routes compared to traditional proximity-based routing. Finally, we discuss implementation issues and propose a solution to dynamically adapt the protocol’s parameter settings.

Density-Based vs. Proximity-Based Anycast Routing for Mobile Networks

This document describes a mechanism to allow for an arbitrary number of Rendevous Points (RPs) per group in a single shared-tree Protocol Independent Multicast-Sparse Mode (PIM-SM) domain.

/pdf/anycast-rendevous-point-rp-mechanism-using-protocol-4ej4p7r391.pdf

D. Kim

Papers

Anycast Rendevous Point (RP) mechanism using Protocol Independent Multicast (PIM) and Multicast Source Discovery Protocol (MSDP)