Network Working Group Christian Vogt Internet-Draft Ericsson Intended status: Informational October 19, 2009 Expires: April 22, 2010 Source Address Validation Improvement Protocol Framework draft-vogt-savi-framework-00 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. 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The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 22, 2010. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Vogt Expires April 22, 2010 [Page 1] Internet-Draft SAVI Protocol Framework October 2009 Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract The Source Address Validation Improvement protocol was developed to complement ingress filtering with finer-grained IP source address validation. To enable the deployment of the SAVI protocol in networks of various kinds, the protocol was designed to be modular and extensible. This document describes and motivates this design, explains how protocol components fit into this framework, and compares the properties of existing protocol components. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Protocol Model . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Deployment Options . . . . . . . . . . . . . . . . . . . . . . 5 4. Scalability Optimizations . . . . . . . . . . . . . . . . . . . 5 5. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . 7 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8 Vogt Expires April 22, 2010 [Page 2] Internet-Draft SAVI Protocol Framework October 2009 1. Introduction While ingress filtering [BCP38] provides a way to validate IP source addresses at an aggregated level, there is not yet a standardized mechanism for IP source address validation at a finer granularity. Having a finer granularity would be helpful in a number of situations, including filtering traffic from customer interfaces implemented as ports in an IP-aware switch or a router, or general improvements in filtering accuracy in enterprise networks. Depending on the situation, there may be a requirement for blocking spoofed packets or merely logging packets that appear to be spoofed. Partial solutions exist to prevent hosts from spoofing the IP source address of another host in the same IP link (e.g., the "IP source guard"), but are proprietary. The purpose of the IETF working group on Source Address Validation Improvements, SAVI, is to standardize a protocol, henceforth called the "SAVI protocol", that prevent hosts attached to the same IP link from spoofing each other's IP addresses. These methods are to complement ingress filtering with finer-grained protection. To enable the deployment of the SAVI protocol in networks of various kinds, the protocol was designed to be modular and extensible. This document describes and motivates this design, explains how protocol components fit into this framework, and compares the properties of existing protocol components. 2. Protocol Model Since the IP source address of a packet generally takes no role in forwarding and can therefore be selected arbitrarily at the time of packet transmission without jeopardizing packet delivery, methods for IP source address validation must augment packet forwarding with an explicit check on whether a given packet's IP source address is legitimate. Such check can happen at different granularity: The classic standard for IP source address validation, ingress filtering [BCP38], functions at the granularity of networks. It achieves this by verifying that the prefix of an IP source address routes to the network from which the packet was received. An advantage of ingress filtering is simplicity, because the decision of whether to accept or to reject an IP source address can be made solely based on the information available from routing protocols. A disadvantage of ingress filtering is that it is insufficient for finer-grained IP source address validation, due to the aggregated nature of the information available from routing protocols. The SAVI protocol was designed to overcome this disadvantage, by providing IP source address validation at the granularity of individual IP addresses. Vogt Expires April 22, 2010 [Page 3] Internet-Draft SAVI Protocol Framework October 2009 This happens in three steps: 1. Identifying which IP source addresses are legitimate for a host, based on monitoring packets exchanged by the host. 2. Binding a legitimate IP address to a physical-layer or link-layer property of the host's network attachment. This property, called a "binding anchor", must be verifiable in every packet that the host sends, and harder to spoof than the host's IP source address itself. 3. Enforcing that the IP source addresses in packets match the binding anchors to which they were bound. The functioning of the SAVI protocol allows for multiple forms of deployment, since a SAVI protocol instance may be located anywhere on the IP link to which the hosts attach. One way to locate a SAVI protocol instance is in the hosts' default router. Thus, IP source addresses are validated in packets traversing the default router, yet the IP source addresses in packets exchanged locally on the IP link may bypass validation. Another way to locate a SAVI protocol instance is in a switch between the hosts and their default router. Thus, packets may undergo IP source address validation even if exchanged locally on the link. The closer a SAVI protocol instance is located to the hosts, the more effective the SAVI protocol is. This is because each of the three steps in which the SAVI protocol validates IP source addresses can best be accomplished in a position close to the host: 1. Identifying a host's legitimate IP source addresses is most efficient close to the host, because the likelihood that the host's packets bypass a SAVI protocol instance, and hence cannot be monitored, increases with the distance between the protocol instance and the host. 2. Selecting a binding anchor for a host's IP source address is easiest close to the host, because the properties of an IP link's physical layer and link layer are unique for a given host only on the link segment directly attaching to the host. 3. Enforcing a host's use of an legitimate IP source address is most reliable when pursued close to the host, because the likelihood that the host's packets bypass a SAVI protocol instance, and hence do not undergo IP source address validation, increases with the distance between the protocol instance and the host. The preferred location of SAVI protocol instances is therefore close Vogt Expires April 22, 2010 [Page 4] Internet-Draft SAVI Protocol Framework October 2009 to hosts, such as in switches that directly attach to the hosts whose IP source addresses are being validated. 3. Deployment Options The functioning of the SAVI protocol, as summarized by the three steps listed in Section 2, is deployment-specific in two ways: 1. The identification of legitimate IP source addresses is dependent on the IP address assignment method in use on a link, since it is through assignment that a host becomes the legitimate user of an IP source address. 2. Binding anchors are dependent on the technology used to build the link on which they are used, as binding anchors are link layer properties of a host's network attachment. To facilitate the deployment of the SAVI protocol in networks of various types, the SAVI protocol is designed in a modular and extensible manner, so as to support different IP address configuration methods and to function with various binding anchors. Naturally, both the permitted IP address assignment methods and the selection of a type of binding anchor have an impact on the strength of IP source address validation. This impact is explained in the first sub-section below. The impact on strength further motivates a priority to resolve situations where a single IP source address is attempted to be bound to different binding anchors through different IP address assignment methods. This prioritization is explained in the second sub-section below. 3.1. IP Address Assignment Methods Enumeration and prioritization of IP address assignment methods to be added. 3.2. Binding Anchors Enumeration of binding anchors to be added, along with a discussion of the security properties of those. 4. Scalability Optimizations The preference to locate SAVI protocol instances close to hosts implies that multiple SAVI protocol instances must be able to co- exist in order to support large IP links. Although the SAVI protocol functions independently of the number of protocol instances per IP Vogt Expires April 22, 2010 [Page 5] Internet-Draft SAVI Protocol Framework October 2009 link, co-existence of multiple protocol instances without further measures can lead to high memory requirements: Since each SAVI protocol instance creates bindings for the IP source addresses of all hosts on the IP link, bindings are replicated across multiple protocol instances. High memory requirements, in turn, increase the cost of a SAVI protocol instance. This is problematic in particular for SAVI protocol instances that run on a switch, since it may significantly increase the cost of such a switch. To reduce the memory requirements for SAVI protocol instances on IP links with multiple protocol instances, the SAVI protocol enables the storage of bindings without replication. This requires manual disabling of IP source address validation on switch ports that connect to other switches running a SAVI protocol instance. Each SAVI protocol instance is then responsible for validating IP source addresses only on those ports to which hosts either attach directly, or through other switches without a SAVI protocol instance. On ports towards other switches running a SAVI protocol instance, IP source addresses are not validated. The switches running SAVI protocol instances thus form a "protection perimeter". The IP source addresses in packets passing the protection perimeter are validated by the ingress SAVI protocol instance, but no further validation takes place as long as the packets remain within, or leave the protection perimeter. Figure Figure 1 illustrates the concept of the protection perimeter. The figure shows an IP link with six switches, of which four, denoted "SAVI switch", run a SAVI protocol instance. The protection perimeter created by the four SAVI protocol instances is shown as a dotted line in the figure. IP source address validation is enabled on all switch ports on the protection perimeter, and it is disabled on all other switch ports. Four hosts, denoted A through D in the figure, attach to the protection perimeter. In the example of figure Figure 1, the protection perimeter includes one of the legacy switches, located in the middle of the depicted IP link topology. This is useful because it enables a single, unpartitioned protection perimeter. A single protection perimeter minimizes memory requirements for the SAVI protocol instances, because every binding is kept only once, namely, by the SAVI protocol instance that attaches to the host being validated. Excluding the legacy switch from the protection perimeter would result in two smaller protection perimeters to the left and to the right of the depicted IP link topology. The memory requirements for the SAVI protocol instances would then be higher: Since IP source address validation would be activated on the two ports connecting to the legacy switch, the SAVI protocol instances adjacent to the legacy switch would replicate all bindings from the respective other Vogt Expires April 22, 2010 [Page 6] Internet-Draft SAVI Protocol Framework October 2009 protection perimeter. The reason why it is possible to include the legacy switch in the protection perimeter is because the depicted IP link topology guarantees that packets cannot enter the protection perimeter via this legacy switch. Without this guarantee, the legacy switch would have to be excluded from the protection perimeter in order to ensure that packets entering the protection perimeter undergo IP source address validation. .............. protection perimeter --> : +--------+ : +---+ +---+ : | SAVI | : | A | | B | <-- hosts : | switch | : +---+ +---+ : +--------+ : ...|......|.............................: | : : +--------+ +--------+ +--------+ : : | SAVI |----------| legacy | | SAVI | : : | switch | | switch |----------| switch | : : +--------+ +--------+ +--------+ : : | ...............................|........: : +--------+ : +--------+ : | SAVI | : | legacy | : | switch | : | switch | : +--------+ : +--------+ :............: | | +---+ +---+ hosts --> | C | | D | +---+ +---+ Figure 1: Protection perimeter concept 5. Acknowledgment The author would like to thank the SAVI working group for a thorough technical discussion on the design and the framework of the SAVI protocol, as captured in this document. This document was generated using the xml2rfc tool. 6. References [BCP38] Paul, P. and D. Senie, "Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing", RFC 2827, BCP 38, May 2000. Vogt Expires April 22, 2010 [Page 7] Internet-Draft SAVI Protocol Framework October 2009 Author's Address Christian Vogt Ericsson 200 Holger Way San Jose, CA 95134 United States Email: christian.vogt@ericsson.com Vogt Expires April 22, 2010 [Page 8]