SAVNET Working Group W. Wang Internet-Draft A. Wang Intended status: Standards Track China Telecom Expires: 22 August 2025 18 February 2025 Intra-domain Source Address Validation (SAV) Solution Based on BM-SPF draft-wang-savnet-intra-domain-solution-bm-spf-00 Abstract This draft proposes a new intra-domain Source Address Validation (SAV) solution. This solution leverages the Bidirectional Metric- based Shortest Path First (BM-SPF) mechanism to avoid the complexity introduced by asymmetric routing for source address validation. It allows intra-domain routers to generate directly the SAV rule from the router's FIB table, based on the reality that the source and destination interface will be same if the IGP domain is symmetric assured. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 22 August 2025. Copyright Notice Copyright (c) 2025 IETF Trust and the persons identified as the document authors. All rights reserved. Wang & Wang Expires 22 August 2025 [Page 1] Internet-Draft BM-SPF-SAVNET February 2025 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions used in this document . . . . . . . . . . . . . . 3 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. The Procedure of this Mechanism . . . . . . . . . . . . . . . 3 4.1. SAV Procedure on AS Border Routers . . . . . . . . . . . 5 4.2. SAV Procedure on Customer-facing or Host-facing Routers . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.3. SAV Procedure on Internal Routers . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 7. Normative References . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction [I-D.ietf-savnet-intra-domain-architecture] proposed two use cases to describe the problems of existing intra-domain SAV mechanisms, and mentioned the intra-domain Source Address Validation (SAV) aims to achieve the following objectives: * To prevent outbound packets from intra-domain subnets (such as host networks or customer networks) from spoofing the source addresses of other intra-domain subnets or other Autonomous Systems (ASes) * To prevent inbound packets from external ASes from spoofing the source addresses of the local AS To achieve these goals, intra-domain SAV needs to focus on the validation mechanisms at three types of routers: host-facing routers, customer-facing routers, and AS border routers. Specifically, host- facing or customer-facing routers need to intercept spoofed packets from the connected networks whose source IP addresses do not belong to those networks. AS border routers need to intercept spoofed packets from other ASes whose source IP addresses belong to the local AS. Wang & Wang Expires 22 August 2025 [Page 2] Internet-Draft BM-SPF-SAVNET February 2025 It is better to find one general solution that can cover all of the above routers, increase the flexibility of intra-SAV deployment within the operator's network. The main challenge for such general solution is how to assure the symmetric routing on routers within the IGP domain. If such challenge is solved, the behavior of edge router(host facing, or customer facing), internal router(the best deployment point for the spine-leaf topology) and AS border router will be same: the SAV can be generated automatically based on the FIB table. [I-D.wang-lsr-bidirectional-metric-spf] proposes a mechanism to accomplish the Shortest Path First (SPF) calculation based on the bidirectional metrics of the links. Under such mechanism, the bidirectional link metrics that are used by the two neighbors to implement the SPF algorithm to calculate the path will be same, which can avoid the asymmetric routing, and them simplify the generation of SAV rule on intra domain IGP routers. 2. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] . 3. Terminology The following terms are used in this draft: BM-SPF: Bidirectional Metric based Shortest Path First Mechanism, defined in [I-D.wang-lsr-bidirectional-metric-spf]. 4. The Procedure of this Mechanism [I-D.wang-lsr-bidirectional-metric-spf] introduces the BM-SPF router capabilities announcement. Once the routers within the IGP domain know all of routers within its domain support and enable the BM-SPF feature, it can safely generate the SAV based on its FIB table. Figure 1 depicts an example of an AS that all routers within it support BM-SPF. Wang & Wang Expires 22 August 2025 [Page 3] Internet-Draft BM-SPF-SAVNET February 2025 + Packets with | spoofed P1/P2 +-------------------------+-------------------------+ | | | | AS \/ | | +---+#+----+ | | | Router 1 | | | +----------+ | | | | | | | | +----------+ | | | Router 2 | | | +----------+ | | / | \ | | / | \ | | / | \ | | 10.0.1.0/16 / |10.0.1.0/16 \ | | 10.0.1.1/24 / |10.0.1.2/24 \ | | +----------+ +----------+ +----------+ | | | Router 3 | | Router 4 | | Router 5 | | | +-----+#+--+ +---+#+----+ +---+#+----+ | | \ / | | | \ / | | | \ / | | | +---------------+ +-------+-------+ | | | Customer | | Host | | | | Network | | Network | | | | (P1) | | (P2) | | | +---------------+ +---------------+ | | | +---------------------------------------------------+ Figure 1: An example of an AS that all routers within it support BM-SPF In an AS that has fully deployed BM-SPF, the bidirectional metric values for SPF calculation on each path are the same. This indicates that when two routers are communicating, the packets between them will be transmitted through the same path. That is to say, when any router within this AS communicates with a peer, whether it is sending packets to that peer or receiving packets from that peer, the same interface is used. In this case, since there is no asymmetric routing, strict uRPF can be safely deployed on any router within the AS to form one SAV defence boundary. Typically, in spine-leaf topology scenario, if we deploy strict uRPF on the spine router, it can prevent leaves connected to the same spine node from spoofing each other, and also the address of other ASes, thus reduces the burden to deploy SAV mechanism on every edge router, as that in conventional deployment. Wang & Wang Expires 22 August 2025 [Page 4] Internet-Draft BM-SPF-SAVNET February 2025 4.1. SAV Procedure on AS Border Routers In Figure 1, Router 1 (the border router) has all the intra-domain prefixes that learned from the IGP protocol. It can generates simply an blocklist containing all these prefixes on interface '#', which is bordered with other AS. When Router 1 receives packets with spoofed P1/P2 from interface ‘#’, the packets will be blocked from entering the AS because the source addresses of these packets are included in the blocklist of Router 1. If Router 1 receives the packet with spoofed source address of the links within the AS, it can also block them automatically. 4.2. SAV Procedure on Customer-facing or Host-facing Routers In Figure 1, the customer network is multi-homed and the host network is single-homed. Router 3 and Router 4 are customer-facing routers, and Router 5 is host-facing router. For single-homed host network, Router 5 need only deploy strict uRPF to achieve the desired effect that interface ‘#’ on Router 5 prevents other spoofed packets(source address is not from P2) from being accepted. For multi-homed customer network, to achieve the effect of engineering return traffic based on the granular address space, two kinds of routes(coarse and granular) should be configured on the customer-facing routers, as shown in Figure 1. On Router 3, a coarse route 10.0.1.0/16 and a granular route 10.0.1.1/24 are configured. On Router 4, a coarse route 10.0.1.0/16 and a granular route 10.0.1.2/24 are configured. These edge routers(Router 3 and Router 4) can need only also deploy strict uRPF to achieve the desired effect. For example, if the packet with source address 10.0.1.2 are coming from interface '#' of Router 3, although it doesn't match the granular FIB entry of 10.0.1.1/24, it match the coarse route 10.0.1.0/16, then the incoming traffic will not be blocked by Router 3. The situation is same for the traffic with source address of 10.0.1.1 that arrives on Router 4. Wang & Wang Expires 22 August 2025 [Page 5] Internet-Draft BM-SPF-SAVNET February 2025 4.3. SAV Procedure on Internal Routers Deploy the intra-domain SAV mechanism on edge routers and AS border router can solve the intra-domain SAV problem. But in some spine- leaf scenario, there is more efficient deployment point to achieve the same goal. For example, in Figure 1, Router 2 is the spine router, with its three leaf routers(Router 3、Router 4、Router 5). Instead of deploy the intra-domain SAV mechanism on these leaf routers, the operator can select deploy it only on the spine Router 2. Once the Router 2 deploys the strict uRPF, it can safely block the spoofed packet from the host or customer network. In summary, SAV procedures in internal router, host-facing, customer- facing are all same. The procedures in AS border router can easily cover the prefixes from host network, customer network and internal links. Then the intra-domain SAV BM-SPF based solution can easily cover all of the scenarios that are described in [I-D.ietf-savnet-intra-domain-problem-statement]. 5. Security Considerations The security considerations described in [I-D.ietf-savnet-intra-domain-problem-statement] and [I-D.ietf-savnet-intra-domain-architecture] also applies to this document. 6. IANA Considerations None 7. Normative References [I-D.ietf-savnet-intra-domain-architecture] Li, D., Wu, J., Qin, L., Geng, N., and L. Chen, "Intra- domain Source Address Validation (SAVNET) Architecture", Work in Progress, Internet-Draft, draft-ietf-savnet-intra- domain-architecture-01, 14 October 2024, . [I-D.ietf-savnet-intra-domain-problem-statement] Li, D., Wu, J., Qin, L., Huang, M., and N. Geng, "Source Address Validation in Intra-domain Networks Gap Analysis, Problem Statement, and Requirements", Work in Progress, Internet-Draft, draft-ietf-savnet-intra-domain-problem- statement-11, 17 February 2025, . Wang & Wang Expires 22 August 2025 [Page 6] Internet-Draft BM-SPF-SAVNET February 2025 [I-D.wang-lsr-bidirectional-metric-spf] Wang, A., "Bidirectional Metric based Shortest Path First Mechanism", Work in Progress, Internet-Draft, draft-wang- lsr-bidirectional-metric-spf-00, 10 February 2025, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . Authors' Addresses Wei Wang China Telecom Beiqijia Town, Changping District Beijing Beijing, 102209 China Email: weiwang94@foxmail.com Aijun Wang China Telecom Beiqijia Town, Changping District Beijing Beijing, 102209 China Email: wangaj3@chinatelecom.cn Wang & Wang Expires 22 August 2025 [Page 7]