]> China Mobile

CN yangfeng@chinamobile.com

New H3C Technologies

CN linchangwang.04414@h3c.com

RTG SPRING SRv6 is being rapidly deployed and is currently primarily used in trusted-domain backbone networks. Both the carrier market and the enterprise market are adopting SRv6 for end-to-end service delivery. However, if a firewall exists along an SRv6 path, legitimate SRv6 traffic will be dropped. This proposal addresses this issue by using SID as source address in SRv6 packets.

Introduction SRv6 is being rapidly deployed and is currently primarily used in trusted-domain backbone networks. Both the carrier market and the enterprise market are adopting SRv6 for end-to-end service delivery. However, if a firewall exists along an SRv6 path, legitimate SRv6 traffic will be dropped. This proposal addresses this issue by using SID as source address in SRv6 packets. The reason has been elaborated in Section 8.1 of . In brief, SRv6 using loopback as source address will cause asymmetric address, which will be blocked by the firewall. As a result, users are forced to encapsulate traffic with multiple layers of tunnel headers—such as IPSec or L2TP—to ensure it can pass through the firewall. This approach introduces two significant issues: first, it increases overhead—for example, IPSec adds approximately 80 bytes of header overhead; second, it undermines the programmability benefits of SRv6, as forwarding is performed based on IPSec rather than SRv6 itself.

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.

Using SRv6 SID as Source Address SRv6 endpoints typically create many SIDs. This section describes the method for selecting a SID as the source address.

User Traffic There are several cases for using SRv6 SID as source address.

L2 VPN Virtual Private Wire Service(VPWS) For L2 VPN VPWS case, the user traffic towards SRv6 SD-WAN backbone will be encapsulated in SRv6 tunnel. When constructing an SRv6 packet, the source address field of the SRv6 packet should be assigned with the local VPN SID value of the PE device. The local VPN SID value can be determined by L2 Cross-Connect.

L2 VPN Virtual Private LAN Service(VPLS) For L2 VPN VPLS, the user traffic towards SRv6 backbone will be encapsulated in SRv6 tunnel. When constructing an SRv6 packet, the source address field of the SRv6 packet should be assigned with the local VPN SID value of the PE device. The local VPN SID value can be determined by L2 VPN VPLS.

L3 IPv4/IPv6 VPN Service For L3 IPv4/IPv6 VPN Service case, the user traffic towards SRv6 backbone will be encapsulated in SRv6 tunnel. When constructing an SRv6 packet, the source address field of the SRv6 packet should be assigned with the local VPN SID value of the PE device. The local VPN SID value can be determined by the L3 IPv4/IPv6 VPN.

Control Traffic Control traffic will not be terminated by VPN, thus will not be impacted.

OAM Traffic OAM traffic terminated by the SRv6 tunnel may use the SRv6 SID as source address, such as ping, trace. Refer to RFC 8986 4.1.1, Allowing the processing of specific Upper-Layer header types is useful for Operations, Administration, and Maintenance (OAM). As an example, an operator might permit pinging of SIDs. To do this, they may enable local configuration to allow Upper-Layer header type 58(ICMPv6).

Management Traffic Management traffic will not be terminated by VPN, thus should not be impacted.

Use Cases

SRv6 Network with SR-aware Stateful Firewall

Problem Statement To provide VPN service in an SRv6 network , the ingress PE encapsulates the payload in an outer IPv6 header with the Segment Routing Header (SRH) 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 . 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 table if there is an active connection between identified by 3 tuple or 5 tuple. Thus only legitimate packets are allowed to be transmitted across it. and 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.

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 * ********************** ********************** ]]>

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 * ********************** ********************** ]]>

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 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 <source, destination> tuple of the packet from PE1 to PE2 is <PE1-IP-ADDR, PE2-VPN-SID>, and the other direction is <PE2-IP-ADDR, PE1-VPN-SID>. 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 flow, and they may be blocked by the firewall.

Solution for SRv6 Traffic Pass Thru SR-aware Stateful Firewall In the SRv6-based VPN service, the final destination of the outer IPv6 header is the VPN-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 unify the semantic of the source and destination address thus ensure the symmetry of the bidirectional flow. When an ingress PE receives the client packet from CE, it checks which L3 VPN service it belongs to, and uses the VPN-SID associated with that L3 VPN service as the source address when encapsulating the outer IPv6 header with the optional SRH.

According to and , 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.

IANA Considerations This document has no IANA actions.

Security Considerations TBD.

This document specifies version 6 of the Internet Protocol (IPv6). It obsoletes RFC 2460. Segment Routing (SR) leverages the source routing paradigm. A node steers a packet through an ordered list of instructions, called "segments". A segment can represent any instruction, topological or service based. A segment can have a semantic local to an SR node or global within an SR domain. SR provides a mechanism that allows a flow to be restricted to a specific topological path, while maintaining per-flow state only at the ingress node(s) to the SR domain. SR can be directly applied to the MPLS architecture with no change to the forwarding plane. A segment is encoded as an MPLS label. An ordered list of segments is encoded as a stack of labels. The segment to process is on the top of the stack. Upon completion of a segment, the related label is popped from the stack. SR can be applied to the IPv6 architecture, with a new type of routing header. A segment is encoded as an IPv6 address. An ordered list of segments is encoded as an ordered list of IPv6 addresses in the routing header. The active segment is indicated by the Destination Address (DA) of the packet. The next active segment is indicated by a pointer in the new routing header. Segment Routing can be applied to the IPv6 data plane using a new type of Routing Extension Header called the Segment Routing Header (SRH). This document describes the SRH and how it is used by nodes that are Segment Routing (SR) capable. The Segment Routing over IPv6 (SRv6) Network Programming framework enables a network operator or an application to specify a packet processing program by encoding a sequence of instructions in the IPv6 packet header. Each instruction is implemented on one or several nodes in the network and identified by an SRv6 Segment Identifier in the packet. This document defines the SRv6 Network Programming concept and specifies the base set of SRv6 behaviors that enables the creation of interoperable overlays with underlay optimization. This document describes an updated version of the "Security Architecture for IP", which is designed to provide security services for traffic at the IP layer. This document obsoletes RFC 2401 (November 1998). [STANDARDS-TRACK] This document defines procedures and messages for SRv6-based BGP services, including Layer 3 Virtual Private Network (L3VPN), Ethernet VPN (EVPN), and Internet services. It builds on "BGP/MPLS IP Virtual Private Networks (VPNs)" (RFC 4364) and "BGP MPLS-Based Ethernet VPN" (RFC 7432). 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. 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. This document provides a security framework for Multiprotocol Label Switching (MPLS) and Generalized Multiprotocol Label Switching (GMPLS) Networks. This document addresses the security aspects that are relevant in the context of MPLS and GMPLS. It describes the security threats, the related defensive techniques, and the mechanisms for detection and reporting. This document emphasizes RSVP-TE and LDP security considerations, as well as inter-AS and inter-provider security considerations for building and maintaining MPLS and GMPLS networks across different domains or different Service Providers. This document is not an Internet Standards Track specification; it is published for informational purposes. Cisco Systems, Inc. China Mobile Cisco Systems, Inc. Bell Canada Huawei Orange Mellanox AT&T Nokia Universita di Roma "Tor Vergata" This document defines data plane functionality required to implement service segments and achieve service programming in SR-enabled MPLS and IPv6 networks, as described in the Segment Routing architecture. Energy Sciences Network Huawei China Unicom Telefonica SI6 Networks SRv6 is a traffic engineering, encapsulation and steering mechanism utilizing IPv6 addresses to identify segments in a pre-defined policy. This document discusses security considerations in SRv6 networks, including the potential threats and the possible mitigation methods. The document does not define any new security protocols or extensions to existing protocols.