Network Working Group F. Yang Internet Draft China Mobile Intended status: Informational C. Lin Expires: September 7, 2023 M. Chen New H3C Technologies March 7, 2023 Considerations for SRv6-based VPN across SR-aware Stateful Firewall draft-yang-spring-srv6-vpn-across-state-firewall-00 Abstract This document describes a problem caused by asymmetrical source/destination address tuple when the VPN traffics pass through an SR-aware stateful firewall in the SRv6 network. A solution for that problem is also proposed. 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), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on September 7, 2023. Copyright Notice Copyright (c) 2023 IETF Trust and the persons identified as the document authors. All rights reserved. Yang, et al. Expire September 7, 2023 [Page 1] Internet-Draft SRv6 VPN across Stateful Firewall March 2023 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction...................................................2 1.1. Requirements Language.....................................3 2. Problem........................................................3 3. Solution.......................................................5 4. Security Considerations........................................6 5. IANA Considerations............................................6 6. References.....................................................6 6.1. Normative References......................................6 6.2. Informative References....................................7 Authors' Addresses................................................8 1. Introduction Segment Routing (SR) [RFC8402] leverages the source routing paradigm. A node steers a packet through an SR Policy instantiated as an ordered list of instructions called "segments". Segment Routing (SR) can be applied to the IPv6 data plane using Segment Routing Header (SRH) [RFC8754], which is called SRv6. To provide VPN service in an SRv6 network [RFC9252], the ingress PE encapsulates the payload in an outer IPv6 header with the Segment Routing Header (SRH) [RFC8754] carrying the SR Policy segment list along with the VPN Service SID. If the VPN service is with best- effort connectivity, the destination address of the outer IPv6 header carries the VPN service SID and the SRH is omitted. Along the forwarding path in the SRv6 network, firewalls may be deployed to filter the traffics. If a firewall is SR-aware, it will retrieve the final destination of an SRv6 packet from the last entry in the SRH rather than the destination address field of the IPv6 header [I-D.ietf-spring-sr-service-programming]. A stateful firewall keeps a track of the state of the network connections traveling across it. Whenever a packet arrives to seek permission to pass through it, the firewall checks from its state Yang, et al. Expires September 7, 2023 [Page 2] Internet-Draft SRv6 VPN across Stateful Firewall March 2023 table if there is an active connection identified by 3 tuple or 5 tuple. Thus only legitimate packets are allowed to be transmitted across it. This document describes a problem caused by asymmetrical source/destination address tuple when the VPN traffics pass through an SR-aware stateful firewall in the SRv6 network. A solution for that problem is also proposed. 1.1. 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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 2. Problem Figure 1 and Figure 2 show the bidirectional VPN traffic packets passing through a firewall in an SRv6 network. The source address of the outer IPv6 header is the IPv6 address of ingress PE. The final destination address of the outer IPv6 header is the VPN Service SID of egress PE. In the SR-Policy-based way, the final destination address is encapsulated in the last entry in the SRH, Segment[0]. In the best-effort way, the SRH is omitted. Yang, et al. Expires September 7, 2023 [Page 3] Internet-Draft SRv6 VPN across Stateful Firewall March 2023 +---+ +---+ +--------+ +---+ +---+ |CE1|---|PE1|--...--|Firewall|--...--|PE2|---|CE2| +---+ +---+ +--------+ +---+ +---+ Packet (PE1 ---> PE2): Packet (PE1 <--- PE2): ********************** ********************** * IPv6 * * IPv6 * * SA=PE1-IP-ADDR * * SA=PE2-IP-ADDR * * DA=NextSegment * * DA=NextSegment * ********************** ********************** * SRH * * SRH * * Seg[0]=PE2-VPN-SID * * Seg[0]=PE1-VPN-SID * * Seg[...] * * Seg[...] * ********************** ********************** * Eth/IPv4/IPv6 * * Eth/IPv4/IPv6 * * Source=CE1 * * Source=CE2 * * Destination=CE2 * * Destination=CE1 * ********************** ********************** * Payload * * Payload * ********************** ********************** Figure 1: SR-Policy-based VPN Traffic across Firewall +---+ +---+ +--------+ +---+ +---+ |CE1|---|PE1|--...--|Firewall|--...--|PE2|---|CE2| +---+ +---+ +--------+ +---+ +---+ Packet (PE1 ---> PE2): Packet (PE1 <--- PE2): ********************** ********************** * IPv6 * * IPv6 * * SA=PE1-IP-ADDR * * SA=PE2-IP-ADDR * * DA=PE2-VPN-SID * * DA=PE1-VPN-SID * ********************** ********************** * Eth/IPv4/IPv6 * * Eth/IPv4/IPv6 * * Source=CE1 * * Source=CE2 * * Destination=CE2 * * Destination=CE1 * ********************** ********************** * Payload * * Payload * ********************** ********************** Figure 2: Best-Effort VPN Traffic across Firewall The stateful firewall will check the association relationships of the bidirectional VPN traffic packets. A common implementation may record the key information of the packets on forward way (internal to external), such as source address and destination address. When receiving a packet on backward way (external to internal), it checks the state table if there is an existing forward packet flow. For Yang, et al. Expires September 7, 2023 [Page 4] Internet-Draft SRv6 VPN across Stateful Firewall March 2023 example, the firewall may require that the source address of packet on backward way matches the destination address of packet on forward way, and destination address will be checked in the similar way. If not matched, the packet on the backward path will be regarded as illegal and thus dropped. An SR-aware firewall is able to retrieve the final destination of an SRv6 packet from the last entry in the SRH. The tuple of the packet from PE1 to PE2 is , and the other direction is . However, the source address of the outer IPv6 packet is usually a loopback interface of the ingress PE. Eventually, the source address and destination address of the forward and backward VPN traffic are regarded as different flows, and they may be blocked by the firewall. 3. Solution In the SRv6-based VPN service, the final destination of the outer IPv6 header is the VPN Service SID of the egress PE, which is associated with that VPN service. But the source address of the outer IPv6 header is usually unrelated to the VPN service. So, it can be difficult for a stateful firewall to establish the association relationship between the bidirectional traffic flows. The proposed solution is to use the ingress PE's own VPN Service SID as the source address of outer IPv6 header, and thus ensure the symmetry of the bidirectional flows. When an ingress PE receives the client packet from CE, it checks which VRF/VSI/XC it belongs to, and uses the VPN Service SID associated with that VRF/VSI/XC as the source address when encapsulating the outer IPv6 header with the optional SRH. Yang, et al. Expires September 7, 2023 [Page 5] Internet-Draft SRv6 VPN across Stateful Firewall March 2023 Outer IPv6 Header of SR-Policy-based VPN Traffic: ********************** ********************** * IPv6 * * IPv6 * * SA=PE1-VPN-SID * * SA=PE2-VPN-SID * * DA=NextSegment * * DA=NextSegment * ********************** ********************** * SRH * * SRH * * Seg[0]=PE2-VPN-SID * * Seg[0]=PE1-VPN-SID * * Seg[...] * * Seg[...] * ********************** ********************** Outer IPv6 Header of Best-effort VPN Traffic: ********************** ********************** * IPv6 * * IPv6 * * SA=PE1-VPN-SID * * SA=PE2-VPN-SID * * DA=PE2-VPN-SID * * DA=PE1-VPN-SID * ********************** ********************** Figure 3: Outer IPv6 Header in the Proposed Solution According to [RFC8402] and [RFC8986], an SRv6 VPN Service SID is an IPv6 address, and it is routable by its Locator prefix in the SRv6 network. In the proposed solution, when an SRv6 VPN Service SID is used as the source address of the outer IPv6 header in the SRv6 network, it is treated as a normal IPv6 address and does not perform any special behavior. 4. Security Considerations TBD. 5. IANA Considerations This document has no IANA actions. 6. References 6.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, May 2017 Yang, et al. Expires September 7, 2023 [Page 6] Internet-Draft SRv6 VPN across Stateful Firewall March 2023 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, July 2018, . [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, . [RFC9252] Dawra, G., Ed., Talaulikar, K., Ed., Raszuk, R., Decraene, B., Zhuang, S., and J. Rabadan, "BGP Overlay Services Based on Segment Routing over IPv6 (SRv6)", RFC 9252, DOI 10.17487/RFC9252, July 2022, . 6.2. Informative References [RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer, D., Matsushima, S., and Z. Li, "Segment Routing over IPv6 (SRv6) Network Programming", RFC 8986, DOI 10.17487/RFC8986, February 2021, . [I-D.ietf-spring-sr-service-programming] Clad, F., Xu, X., Filsfils, C., Bernier, D., Li, C., Decraene, B., Ma, S., Yadlapalli, C., Henderickx, W., and S. Salsano, "Service Programming with Segment Routing", Work in Progress, Internet-Draft, draft-ietf-spring-sr-service-programming-07, 15 February 2023, . Yang, et al. Expires September 7, 2023 [Page 7] Internet-Draft SRv6 VPN across Stateful Firewall March 2023 Authors' Addresses Feng Yang China Mobile China Email: yangfeng@chinamobile.com Changwang Lin New H3C Technologies China Email: linchangwang.04414@h3c.com Mengxiao Chen New H3C Technologies China Email: chen.mengxiao@h3c.com Yang, et al. Expires September 7, 2023 [Page 8]