]> Tsinghua University

Beijing China jianping@cernet.edu.cn

Tsinghua University

Beijing China tolidan@tsinghua.edu.cn

Zhongguancun Laboratory

Beijing China liulb@zgclab.edu.cn

Huawei

Beijing China huangmingqing@huawei.com

Tsinghua University

Beijing China qlc19@mails.tsinghua.edu.cn

Huawei

Beijing China gengnan@huawei.com

General [REPLACE] Internet Engineering Task Force This document provides the gap analysis of existing inter-domain source address validation mechanisms, describes the fundamental problems, and defines the requirements for technical improvements.

Introduction Source address validation (SAV) is crucial for protecting networks from source address spoofing attacks. The MANRS initiative advocates deploying SAV as close to the source as possible , and access networks are the first line of defense against source address spoofing. However, access networks face various challenges in deploying SAV mechanisms due to different network environments, router vendors, and operational preferences. Hence, it is not feasible to deploy SAV at every network edge. Additional SAV mechanisms are needed at other levels of the network to prevent source address spoofing along the forwarding paths of the spoofed packets. The Source Address Validation Architecture (SAVA) proposes a multi-fence approach that implements SAV at three levels of the network: access, intra-domain, and inter-domain. If a spoofing packet is not blocked at the originating access network, intra-domain and inter-domain SAV mechanisms can help block the packet along the forwarding path of the packet. As analyzed in , intra-domain SAV for an AS can prevent a subnet of the AS from spoofing the addresses of other subnets as well as prevent incoming traffic to the AS from spoofing the addresses of the AS, without relying on the collaboration of other ASes. As complementrary, in scenarios where intra-domain SAV cannot work, inter-domain SAV leverages the collaboration among ASes to help block incoming spoofing packets in an AS which spoof the source addresses of other ASes. This document provides an analysis of inter-domain SAV. illustrates an example for inter-domain SAV. P1 is the source prefix of AS 1, and AS 4 sends spoofing packets with P1 as source addresses to AS 3 through AS 2. Assume AS 4 does not deploy intra-domain SAV, these spoofing packets cannot be blocked by AS 4. Although AS 1 can deploy intra-domain SAV to block incoming packets which spoof the addresses of AS 1, these spoofing traffic from AS 4 to AS 3 do not go through AS 1, so they cannot be blocked by AS 1. Inter-domain SAV can help in this scenario. If AS 1 and AS 2 deploy inter-domain SAV, AS 2 knows the correct incoming interface of packets with P1 as source address, and the spoofing packets can thus be blocked by AS 2 since they come from the incorrect interface.

An example for illustrating inter-domain SAV

There are many existing mechanisms for inter-domain SAV. This document analyzes them and attempts to answer: i) what are the technical gaps (), ii) what are the fundamental problems (), and iii) what are the practical requirements for the solution of these problems ().

Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Terminology

SAV Rule:

The rule that indicates the validity of a specific source IP address or source IP prefix.

Improper Block:

The validation results that the packets with legitimate source addresses are blocked improperly due to inaccurate SAV rules.

Improper Permit:

The validation results that the packets with spoofed source addresses are permitted improperly due to inaccurate SAV rules.

Existing Inter-domain SAV Mechanisms Inter-domain SAV is typically performed at the AS level and can be deployed at AS border routers (ASBR) to prevent source address spoofing. There are various mechanisms available to implement inter-domain SAV for anti-spoofing ingress filtering , which are reviewed in this section.

• ACL-based ingress filtering : ACL-based ingress filtering is a technique that relies on ACL rules to filter packets based on their source addresses. It can be applied at provider interfaces, customer interfaces, or peer interfaces of an AS, and is recommended to deploy at provider interfaces or customer interfaces . At the provider interface, ACL-based ingress filtering can block source prefixes that are clearly invalid in the inter-domain routing context, such as suballocated or internal-only prefixes of customer ASes . At the customer interface, ACL-based ingress filtering can prevent customer ASes from spoofing source addresses of other ASes that are not reachable via the provider AS. It can be implemented at border routers or aggregation routers if border ACLs are not feasible . However, ACL-based ingress filtering introduces significant operational overhead, as ACL rules need to be updated in a timely manner to reflect prefix or routing changes in the inter-domain routing system, which requires manual configuration to avoid improper block or improper permit.
• uRPF-based machanisms: A class of SAV mechanisms are based on Unicast Reverse Path Forwarding (uRPF) . The core idea of uRPF for SAV is to exploit the symmetry of inter-domain routing: in many cases, the best next hop for a destination is also the best previous hop for the source. In other words, if a packet arrives from a certain interface, the source address of that packet should be reachable via the same interface, according to the FIB. However, symmetry in routing does not always holds in practice, and to address cases where it does not hold, many enhancements and modes of uRPF are proposed. Different modes of uRPF have different levels of strictness and flexibility, and network operators can choose from them to suit particular network scenarios. We describe these modes as follows:
  • Strict uRPF : Strict uRPF is the most stringent mode, and it only permits packets that have a source address that is covered by a prefix in the FIB, and that the next hop for that prefix is the same as the incoming interface. This mode is recommended for deployment at customer interfaces that directly connect to an AS with suballocated address space, as it can prevent spoofing attacks from that AS or its downstream ASes .
  • Loose uRPF : Loose uRPF verifies that the source address of the packet is routable in the Internet by matching it with one or more prefixes in the FIB, regardless of which interface the packet arrives at. If the source address is not routable, Loose uRPF discards the packet. Loose uRPF is typically deployed at the provider interfaces of an AS to block packets with source addresses that are obviously disallowed, such as non-global prefixes (e.g., private addresses, multicast addresses, etc.) or the prefixes that belong to the customer AS itself .
  • FP-uRPF : FP-uRPF maintains a reverse path forwarding (RPF) list, which contains the prefixes and all their permissible routes including the optimal and alternative ones. It permits an incoming packet only if the packet's source address is encompassed in the prefixes of the RPF list and its incoming interface is included in the permissible routes of the corresponding prefix. FP-uRPF is recommended to be deployed at customer interfaces or peer interfaces, especially those that are connected to multi-homed customer ASes .
  • Virtual routing and forwarding (VRF) uRPF : VRF uRPF uses a separate VRF table for each external BGP peer. A VRF table is a table that contains the prefixes and the routes that are advertised by a specific peer. VRF uRPF checks the source address of an incoming packet from an external BGP peer against the VRF table for that peer. If the source address matches one of the prefixes in the VRF table, VRF uRPF allows the packet to pass. Otherwise, it drops the packet. VRF uRPF can also be used as a way to implement BCP38 , which is a set of recommendations to prevent IP spoofing. However, the operational feasibility of VRF uRPF as BCP38 has not been proven .
  • EFP-uRPF : EFP-uRPF consists of two algorithms, algorithm A and algorithm B. EFP-uRPF is based on the idea that an AS can receive BGP updates for multiple prefixes that have the same origin AS at different interfaces. For example, this can happen when the origin AS is multi-homed and advertises the same prefixes to different providers. In this case, EFP-uRPF allows an incoming packet with a source address in any of those prefixes to pass on any of those interfaces. This way, EFP-uRPF can handle asymmetric routing scenarios where the incoming and outgoing interfaces for a packet are different. EFP-uRPF has not been implemented in practical networks yet, but BCP84 suggests using EFP-uRPF with algorithm B at customer interfaces of an AS. EFP-uRPF can also be used at peer interfaces of an AS.
• Source-based remote triggered black hole (RTBH) filtering : Source-based RTBH filtering enables the targeted dropping of traffic by specifying particular source addresses or address ranges. Source-based RTBH filtering uses uRPF, usually Loose uRPF, to check the source address of an incoming packet against the FIB. If the source address of the packet does not match or is not covered by any prefix in the FIB, or if the route for that prefix points to a black hole (i.e., Null0), Loose uRPF discards the packet. This way, source-based RTBH filtering can filter out attack traffic at specific devices (e.g., ASBR) in an AS based on source addresses, and improve the security of the network.
• Carrier Grade NAT (CGN): CGN is a network technology used by service providers to translate between private and public IPv4 addresses within their network. CGN enables service providers to assign private IPv4 addresses to their customer ASes instead of public, globally unique IPv4 addresses. The private side of the CGN faces the customer ASes, and when an incoming packet is received from a customer AS, CGN checks its source address. If the source address is included in the address list of the CGN's private side, CGN performs address translation. Otherwise, it forwards the packet without translation. However, since CGN cannot determine whether the source address of an incoming packet is spoofed or not, additional SAV mechanisms need to be implemented to prevent source address spoofing .
• BGP origin validation (BGP-OV) : Attackers can bypass uRPF-based SAV mechanisms by using prefix hijacking in combination with source address spoofing. By announcing a less-specific prefix that does not have a legitimate announcement, the attacker can deceive existing uRPF-based SAV mechanisms and successfully perform address spoofing. To protect against this type of attack, a combination of BGP-OV and uRPF-based mechanisms like FP-uRPF or EFP-uRPF is recommended . BGP routers can use ROA information, which is a validated list of {prefix, maximum length, origin AS}, to mitigate the risk of prefix hijacks in advertised routes.

Gap Analysis Inter-domain SAV protects against source address spoofing attacks across all AS interfaces, including provider, customer, and peer interfaces. This section performs a gap analysis of existing SAV mechanisms at these interfaces to identify their technical shortcomings.

SAV at Provider Interface SAV at provider interface is recommended to deploy ACL-based ingress filtering and/or Loose uRPF to prevent spoofing source addresses from provider AS , and can utilize source-based RTBH filtering to configure SAV rules remotely. In the following, we expose the problems with existing inter-domain SAV mechanisms at the provider interface with a reflection attack scenario.

A scenario of the reflection attack from provider AS

As depicted in , a reflection attack is a type of cyber attack in which the attacker spoofs the victim's IP address (P1) and sends requests to server's IP address (P2) that respond to that type of request. The servers then send responses back to the victim, overwhelming its network resources. The arrows represent the commercial relationship between ASes. AS 3 is the provider of AS 4, and AS 4 is the provider of AS 1 and AS 2. Suppose AS 1 and AS 4 have deployed inter-domain SAV, while the other ASes have not. By applying ACL-based ingress filtering at the provider interface of AS 4, the ACL rules can block any packets with spoofed source addresses from AS 3 in P1 and P2, thus stopping the attack. However, this approach incurs heavy operational overhead, as it requires network operators to update the ACL rules promptly based on changes in prefixes or topology of AS 1 and AS 2. Otherwise, it may cause improper block or improper permit of legitimate traffic. Source-based RTBH filtering allows for the deployment of SAV rules on AS 1 and AS 4 remotely. However, in order to avoid improper block or improper permit, the specified source addresses need to be updated in a timely manner, which incurs additional operational overhead. Loose uRPF can greatly reduce the operational overhead because it uses the local FIB as information source, and can adapt to changes in the network. However, it can improperly permit spoofed packets. In , Loose uRPF is enabled at AS 4's provider interface, while EFP-uRPF is enabled at AS 4's customer interfaces, following . An attacker inside AS 3 or connected to it through other ASes may send packets with source addresses spoofing P1 to a server in AS 2 to attack the victim in AS 1. As AS 3 lacks deployment of inter-domain SAV, the attack packets will reach AS 4's provider interface. With Loose uRPF, AS 4 cannot block the attack packets at its provider interface, and thus resulting in improper permit.

SAV at Customer Interface To prevent the spoofing of source addresses within a customer cone, operators can enable ACL-based ingress filtering, source-based RTBH filtering, and/or uRPF-based mechanisms at the customer interface, namely Strict uRPF, FP-uRPF, VRF uRPF, or EFP-uRPF. However, ACL-based ingress filtering and source-based RTBH filtering need to update SAV rules in a timely manner and have the same operational overhead as performing SAV at provider interfaces, while uRPF-based mechanisms may cause improper block problems in two inter-domain scenarios: limited propagation of prefixes and hidden prefixes. In the following, we show how uRPF-based mechanisms may block legitimate traffic.

Limited Propagation of Prefixes In inter-domain networks, some prefixes may not be propagated to all domains due to various factors, such as NO_EXPORT or NO_ADVERTISE communities or other route filtering policies. This may cause asymmetric routing in the inter-domain context, which may lead to false positives when performing SAV with existing mechanisms. These mechanisms include EFP-uRPF, which we focus on in the following analysis, as well as trict uRPF, FP-uRPF, and VRF uRPF. All these mechanisms suffer from the same problem of improper block in this scenario.

Limited propagation of prefixes caused by NO_EXPORT

presents a scenario where the limited propagation of prefixes occurs due to the NO_EXPORT community attribute. AS 1 is the customer of both AS 2 and AS 3, and AS 4 is the provider of AS 2. The relationship between AS 3 and AS 4 can be either customer-to-provider (C2P) or peer-to-peer (P2P). AS 1 advertises prefix P1 to its provider, AS 2 and AS 3. Upon receiving the route for prefix P1 from AS 1, AS 3 propagates it to AS 4. However, AS 2 does not propagate the route for prefix P1 to AS 4 because AS 1 adds the NO_EXPORT community attribute in the BGP advertisement sent to AS 2. In this scenario, AS 4 learns the route for prefix P1 only from AS 3. Suppose AS 1 and AS 4 have deployed inter-domain SAV while other ASes have not, and AS 4 have deployed EFP-uRPF at the customer interface. Assuming that AS 3 is the customer of AS 4, if AS 4 deploys EFP-uRPF with algorithm A at customer interfaces, it will require packets with source addresses in P1 to only arrive from AS 3. When AS 1 sends legitimate packets with source addresses in P1 to AS 4 through AS 2, AS 4 improperly blocks these packets. The same problem applies to Strict uRPF, FP-uRPF, and VRF uRPF. Although EFP-uRPF with algorithm B can avoid improper block in this case, network operators need to first determine whether limited prefix propagation exists before choosing the suitable EFP-uRPF algorithms, which adds more complexity and overhead to network operators. Furthermore, EFP-uRPF with algorithm B is not without its problems. For example, if AS 3 is the peer of AS 4, AS 4 will not learn the route of P1 from its customer interfaces. In such case, both EFP-uRPF with algorithm A and algorithm B have improper block problems.

Hidden Prefixes Some servers' source addresses are not advertised through BGP to other ASes. These addresses are unknown to the inter-domain routing system and are called hidden prefixes. Legitimate traffic with these hidden prefixes may be dropped by existing inter-domain SAV mechanisms, such as Strict uRPF, FP-uRPF, VRF uRPF, or EFP-uRPF, because they do not match any known prefix. For example, Content Delivery Networks (CDN) use anycast to improve the quality of service by bringing content closer to users. An anycast IP address is assigned to devices in different locations, and incoming requests are routed to the closest location. Usually, only locations with multiple connectivity announce the anycast IP address through BGP. The CDN server receives requests from users and creates tunnels to the edge locations, where content is sent directly to users using direct server return (DSR). DSR requires servers in the edge locations to use the anycast IP address as the source address in response packets. However, these edge locations do not announce the anycast prefixes through BGP, so an intermediate AS with existing inter-domain SAV mechanisms may improperly block these response packets.

A Direct Server Return (DSR) scenario

illustrates a DSR scenario where the anycast IP prefix P3 is only advertised by AS 3 through BGP. In this example, AS 3 is the provider of AS 4, and AS 4 is the provider of AS 1 and AS 2. AS 1 and AS 4 have deployed inter-domain SAV, while other ASes have not. When users in AS 1 send requests to the anycast destination IP, the forwarding path is AS 1->AS 4->AS 3. The anycast servers in AS 3 receive the requests and tunnel them to the edge servers in AS 2. Finally, the edge servers send the content to the users with source addresses in prefix P3. The reverse forwarding path is AS 2->AS 4->AS 1. Since AS 4 does not receive routing information for prefix P3 from AS 2, EFP-uRPF with algorithm A/B, and all other existing uRPF-based mechanisms at the customer interface of AS 4 facing AS 2 will improperly block the legitimate response packets from AS 2.

SAV at Peer Interface To prevent spoofing traffic from peer ASes, SAV at peer interfaces can enable ACL-based ingress filtering, source-based RTBH filtering, and/or employ one of the following uRPF-based SAV mechanisms: FP-uRPF, VRF uRPF, or EFP-uRPF. ACL-based ingress filtering and source-based RTBH filtering have high operational overhead and uRPF-based SAV mechanisms share the same improper block problems with the inter-domain SAV mechanisms when applied at provider interfaces or customer interfaces. The improper block problems occur in cases of limited propagation of prefixes and hidden prefixes. For brevity, we do not analyze these problems again here. Moreover, if we apply EFP-uRPF with algorithm B at peer or customer interfaces, we may encounter improper permit problems, as explained below.

A scenario of the reflection attack from peer AS

depicts a scenario of a reflection attack originating from a peer AS. The direction of the commercial relationship between ASes is indicated by arrows. AS 3 is the lateral peer of AS 4, which is the provider of AS 1 and AS 2. Assuming that AS 1 and AS 4 have deployed inter-domain SAV and that EFP-uRPF with algorithm B is enabled at AS 4's peer and customer interfaces, a reflection attacker located in AS 3 or connected to it through other ASes can launch an attack on a victim in AS 1 by sending packets with spoofed source addresses in P1 to a server in AS 2. Since AS 3 does not perform SAV, the spoofed attack packets will arrive at the peer interface of AS 4, EFP-uRPF with algorithm B cannot block them since it allows packets with source addresses in prefix P1 on any of AS 4's peer interfaces.

Problem Statement Based on the above analysis, we conclude that existing inter-domain SAV mechanisms have limitations in asymmetric routing scenarios, and they may cause improper block or improper permit issues. They also incur high operational overhead when network routing changes dynamically. For ACL-based ingress filtering, network operators need to manually update ACL rules to adapt to network changes. Otherwise, they may cause improper block or improper permit issues. Manual updates induce high operational overhead, especially in networks with frequent policy and route changes. Source-based RTBH filtering has the similar problem as ACL-based ingress filtering. Strict uRPF and Loose uRPF are automatic SAV mechanisms, thus they do not need any manual effort to adapt to network changes. However, they have issues in scenarios with asymmetric routing. Strict uRPF may cause improper block problems when an AS is multi-homed and routes are not symmetrically announced to all its providers. This is because the local FIB may not include the asymmetric routes of the legitimate packets, and Strict uRPF only uses the local FIB to check the source addresses and incoming interfaces of packets. Loose uRPF may cause improper permit problems and fail to prevent source address spoofing. This is because it is oblivious to the incoming interfaces of packets. FP-uRPF and VRF uRPF improve Strict uRPF in multi-homing scenarios. However, they still have improper block issues in asymmetric routing scenarios. For example, they may not handle the cases of limited propagation of prefixes. These mechanisms use the local RIB to learn the source prefixes and their valid incoming interfaces. But the RIB may not have all the prefixes with limited propagation and their permissible incoming interfaces. EFP-uRPF allows the prefixes from the same customer cone at all customer interfaces. This solves the improper block problems of FP-uRPF and VRF uRPF in multi-homing scenarios. However, this approach also compromises partial protection against spoofing from the customer cone. EFP-uRPF may still have improper block problems when it does not learn legitimate source prefixes. For example, hidden prefixes are not learned by EFP-uRPF. Finally, existing inter-domain SAV mechanisms cannot work in all directions (i.e. interfaces) of ASes to achieve effective SAV. Network operators need to carefully analyze the network environment and choose approapriate SAV mechansim for each interface. This leads to additional operational and cognitive overhead, which can hinder the rate of adoption of inter-domain SAV.

Requirements for New Inter-domain SAV Mechanisms This section lists the requirements which can help bridge the technical gaps of existing inter-domain SAV mechanisms. These requirements serve as practical guidelines that can be met, in part or in full, by proposing new techniques.

Automatic Update The new inter-domain SAV mechanism MUST be able to adapt to dynamic networks and asymmetric routing scenarios automatically, instead of relying on manual update.

Accurate Validation The new inter-domain SAV mechanism SHOULD improve the validation accuracy in all directions of ASes over existing inter-domain SAV mechanisms. It SHOULD avoid improper block and minimize improper permit so that the legitimate traffic from an AS will not be blocked and the spoofed traffic will be reduced as much as possible. To avoid improper block, ASes that deploy the new inter-domain SAV mechanism SHOULD be able to acquire all the real data-plane forwarding paths. In cases where it is difficult to acquire all the real forwarding paths exactly, it is essential to obtain a minimal set of acceptable paths that cover the real forwarding paths to avoid improper block and minimize improper permit. Additionally, multiple sources of SAV-related information, such as RPKI ROA objects, ASPA objects, and collaborative advertisements of other ASes, can help reduce the set of acceptable paths and improve the validation accuracy.

Working in Incremental/Partial Deployment The new inter-domain SAV mechanism SHOULD NOT assume pervasive adoption and SHOULD provide effective protection for source addresses when it is partially deployed in the Internet. Not all AS border routers can support the new SAV mechanism at once, due to various constraints such as capabilities, versions, or vendors. The new SAV mechanism should not be less effective in protecting all directions of ASes under partial deployment than existing mechanisms.

Inter-domain SAV Scope The new inter-domain SAV mechanism should work in the same scenarios as existing inter-domain SAV mechanisms. Generally, it includes all IP-encapsulated scenarios:

• Native IP forwarding: This includes both global routing table forwarding and CE site forwarding of VPN.
• IP-encapsulated Tunnel (IPsec, GRE, SRv6, etc.): In this scenario, we focus on the validation of the outer layer IP address.
• Both IPv4 and IPv6 addresses.

Scope does not include:

• Non-IP packets: This includes MPLS label-based forwarding and other non-IP-based forwarding.

In addition, the new inter-domain SAV mechanism should not modify data-plane packets. Existing architectures or protocols or mechanisms can be inherited by the new SAV mechanism to achieve better SAV effectiveness.

Security Considerations SAV rules can be generated based on route information (FIB/RIB) or non-route information. If the information is poisoned by attackers, the SAV rules will be false. Legitimate packets may be dropped improperly or malicious traffic with spoofed source addresses may be permitted improperly. Route security should be considered by routing protocols. Non-route information, such as ASPA, should also be protected by corresponding mechanisms or infrastructure. If SAV mechanisms or protocols require information exchange, there should be some considerations on the avoidance of message alteration or message injection. The SAV procedure referred in this document modifies no field of packets. So, security considerations on data-plane are not in the scope of this document.

IANA Considerations This document does not request any IANA allocations.

References Normative References RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. BCP 38, RFC 2827, is designed to limit the impact of distributed denial of service attacks, by denying traffic with spoofed addresses access to the network, and to help ensure that traffic is traceable to its correct source network. As a side effect of protecting the Internet against such attacks, the network implementing the solution also protects itself from this and other attacks, such as spoofed management access to networking equipment. There are cases when this may create problems, e.g., with multihoming. This document describes the current ingress filtering operational mechanisms, examines generic issues related to ingress filtering, and delves into the effects on multihoming in particular. This memo updates RFC 2827. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document identifies a need for and proposes improvement of the unicast Reverse Path Forwarding (uRPF) techniques (see RFC 3704) for detection and mitigation of source address spoofing (see BCP 38). Strict uRPF is inflexible about directionality, the loose uRPF is oblivious to directionality, and the current feasible-path uRPF attempts to strike a balance between the two (see RFC 3704). However, as shown in this document, the existing feasible-path uRPF still has shortcomings. This document describes enhanced feasible-path uRPF (EFP-uRPF) techniques that are more flexible (in a meaningful way) about directionality than the feasible-path uRPF (RFC 3704). The proposed EFP-uRPF methods aim to significantly reduce false positives regarding invalid detection in source address validation (SAV). Hence, they can potentially alleviate ISPs' concerns about the possibility of disrupting service for their customers and encourage greater deployment of uRPF techniques. This document updates RFC 3704. This paper discusses a simple, effective, and straightforward method for using ingress traffic filtering to prohibit DoS (Denial of Service) attacks which use forged IP addresses to be propagated from 'behind' an Internet Service Provider's (ISP) aggregation point. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Because the Internet forwards packets according to the IP destination address, packet forwarding typically takes place without inspection of the source address and malicious attacks have been launched using spoofed source addresses. In an effort to enhance the Internet with IP source address validation, a prototype implementation of the IP Source Address Validation Architecture (SAVA) was created and an evaluation was conducted on an IPv6 network. This document reports on the prototype implementation and the test results, as well as the lessons and insights gained from experimentation. This memo defines an Experimental Protocol for the Internet community. This document describes a method by which a Service Provider may use an IP backbone to provide IP Virtual Private Networks (VPNs) for its customers. This method uses a "peer model", in which the customers' edge routers (CE routers) send their routes to the Service Provider's edge routers (PE routers); there is no "overlay" visible to the customer's routing algorithm, and CE routers at different sites do not peer with each other. Data packets are tunneled through the backbone, so that the core routers do not need to know the VPN routes. [STANDARDS-TRACK] Remote Triggered Black Hole (RTBH) filtering is a popular and effective technique for the mitigation of denial-of-service attacks. This document expands upon destination-based RTBH filtering by outlining a method to enable filtering by source address as well. This memo provides information for the Internet community. To help reduce well-known threats against BGP including prefix mis- announcing and monkey-in-the-middle attacks, one of the security requirements is the ability to validate the origination Autonomous System (AS) of BGP routes. More specifically, one needs to validate that the AS number claiming to originate an address prefix (as derived from the AS_PATH attribute of the BGP route) is in fact authorized by the prefix holder to do so. This document describes a simple validation mechanism to partially satisfy this requirement. [STANDARDS-TRACK] As the Internet has grown, and as systems and networked services within enterprises have become more pervasive, many services with high availability requirements have emerged. These requirements have increased the demands on the reliability of the infrastructure on which those services rely. Various techniques have been employed to increase the availability of services deployed on the Internet. This document presents commentary and recommendations for distribution of services using anycast. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This memo discusses architectural implications of IP anycast and provides some historical analysis of anycast use by various IETF protocols. Informative References MANRS Internet Society NIST Cisco Systems, Inc.

Acknowledgements Many thanks to Jared Mauch, Barry Greene, Fang Gao, Anthony Somerset, Kotikalapudi Sriram, Yuanyuan Zhang, Igor Lubashev, Alvaro Retana, Joel Halpern, Aijun Wang, Michael Richardson, Li Chen, Gert Doering, Mingxing Liu, John O'Brien, Roland Dobbins, etc. for their valuable comments on this document.