]> Energy Sciences Network

buraglio@forwardingplane.net

Huawei

tal.mizrahi.phd@gmail.com

China Unicom

tongt5@chinaunicom.cn

Routing Source Packet Routing in Networking Internet-Draft SRv6 is a traffic engineering, encapsulation, and steering mechanism utilizing IPv6 addresses to identify segments in a pre-defined policy. While SRv6 uses what appear to be typical IPv6 addresses, the address space is treated differently, and in most (all?) cases. A typical IPv6 unicast address is comprised of a network prefix, host identifier, and a subnet mask. A typical SRv6 segment identifier (SID) is broken into a locator, a function identifier, and optionally, function arguments. The locator must be routable, which enables both SRv6 capable and incapable devices to participate in forwarding, either as normal IPv6 unicast or SRv6. The capability to operate in environments that may have gaps in SRv6 support allows the bridging of islands of SRv6 devices with standard IPv6 unicast routing. As standard IPv6 addressing, there are security considerations that should be well understood that may not be obvious. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the Source Packet Routing in Networking Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction Segment Routing (SR) utilizing an IPv6 data plane is a source routing model that leverages an IPv6 underlay and an IPv6 extension header called the Segment Routing Header (SRH) to signal and control the forwarding and path of packets by imposing an ordered list of path details that are processed at each hop along the signaled path. Because SRv6 is fundamentally bound to the IPv6 protocol, and because of the reliance of a new header there are security considerations which must be noted or addressed in order to operate an SRv6 network in a reliable and secure manner.

• SRv6 makes use of the SRH which is a new type of Routing Extension Header. Therefore, the security properties of the Routing Extension Header are addressed by the SRH. See and for details.
• SRv6 consists of using the SRH on the IPv6 dataplane which security properties can be understood based on previous work , , and .

This document describes various threats to SRv6 networks and also presents existing approaches to avoid or mitigate the threats.

Conventions and Definitions 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. SRv6 Locator Block FRR SID uSID SRH

Threat Model This section introduces the threat model that is used in this document. The model is based on terminology from the Internet threat model , as well as some concepts from and . Details regarding inter-domain segment routing (SR) are out of scope for this document.

Security Components The main components of information security are confidentiality, integrity and availability, often referred to by the acronym CIA. A short description of each of these components is presented below in the context of SRv6 security.

Confidentiality The purpose of confidentiality is to protect the user data from being exposed to unauthorized users, i.e., preventing attackers from eavesdropping to user data. The confidentiality of user data is outside the scope of this document. However, confidentiality aspects of SRv6-related information are within the scope; collecting information about SR endpoint addresses, SR policies, and network topologies, is a specific form of reconnaissance, which is further discussed in TBD.

Integrity Preventing information from being modified is a key property of information security. Other aspects of integrity include authentication, which is the ability to verify the source of information, and authorization, which enforces different permission policies to different users or sources. In the context of SRv6, compromising the integrity may result in packets being routed in different paths than they were intended to be routed through, which may have various implications, as further discussed in TBD.

Availability Protecting the availability of a system means keeping the system running continuously without disruptions. The availability aspects of SRv6 include the ability of attackers to leverage SRv6 as a means for compromising the performance of a network or for causing Denial of Service (DoS).

Threat Abstractions A security attack is implemented by performing a set of one or more basic operations. These basic operations (abstractions) are as follows:

• Passive listening: an attacker who reads packets off the network can collect information about SR endpoint addresses, SR policies and the network topology. This information can then be used to deploy other types of attacks.
• Packet replaying: in a replay attack the attacker records one or more packets and transmits them at a later point in time.
• Packet insertion: an attacker generates and injects a packet to the network. The generated packet may be maliciously crafted to include false information, including for example false addresses and SRv6-related information.
• Packet deletion: by intercepting and removing packets from the network, an attacker prevents these packets from reaching their destination. Selective removal of packets may, in some cases, cause more severe damage than random packet loss.
• Packet modification: the attacker modifies packets during transit.

Threat Taxonomy The threat terminology used in this document is based on . Threats are classified according to two main criteria: internal vs. external attackers, and on-path vs. off-path attackers, as discussed in .

Internal vs. External:

An internal attacker in the context of SRv6 is an attacker who is located within an SR domain. Specifically, an internal attacker either has access to a node in the SR domain, or is located on an internal path between two nodes in the SR domain. In this context, the latter means that the attacker can be reached from a node in the SR domain without traversing an SR egress node, and can reach a node in the SR domain without traversing an SR ingress node. External attackers, on the other hand, are not within the SR domain.

On-path vs. Off-path:

On-path attackers are located in a position that allows interception, modification or dropping of in-flight packets, as well as insertion (generation) of packets. Off-path attackers can only attack by insertion of packets.

The following figure depicts the attacker types according to the taxonomy above. As illustrated in the figure, on-path attackers are located along the path of the traffic that is under attack, and therefore can listen, insert, delete, modify or replay packets in transit. Off-path attackers can insert packets, and in some cases can passively listen to some of the traffic, such as multicast transmissions.

Threat Model Taxonomy X---------->O------>X------->O------->O----> ^\ ^ /^ | \___/\_ /\_ | _/\__/ | | \__/ | | | | | SR SR SR ingress endpoint egress node node ]]>

It should be noted that in some threat models the distinction between internal and external attackers depends on whether an attacker has access to a trusted or secured (encrypted or authenticated) domain. The current model defines the SR domain as the boundary that distinguishes internal from external threats, and does not make an assumption about whether the SR domain is secured or not. However, it can be assumed that the SR domain defines a trusted domain with respect to SRv6, and thus that external attackers are outside of this trusted domain.

Security Considerations in Operational SRv6 Enabled Networks

Encapsulation of packets

Allowing potential circumvention of existing network ingress / egress policy. SRv6 packets rely on the routing header in order to steer traffic that adheres to a defined SRv6 traffic policy. This mechanism supports not only use of the IPv6 routing header for packet steering, it also allows for encapsulation of both IPv4 and IPv6 packets. IPv6 routing header

Default allow failure mode Use of GUA addressing in data plane programming could result in an fail open scenario when appropriate border filtering is not implemented or supported.

Segment Routing Header SRv6 routing header The attacks can be lunched by constructing segment lists to define any traffic forwarding path. For example: Attackers change the tail SID in Segment List to forward traffic to unexpected destinations; Attackers delete the SID in Segment List to prevent packets from being processed, such as bypassing the billing service and security detection; Attackers add the SID in Segment List to get various unauthorized services, such as traffic acceleration; Broadband DoS/DDoS attacks:The attacks can be launched by constructing segment lists，such as inserting duplicate SRv6 address into segment lists,to make packets be forwarded repeatedly between two or more routers or hosts on specific links..Typically, the Segment List length of SRH is limited, but when SRv6 head compression technology is used, the number of package compression SIDs in SRH increases, and the amplification effect of traffic is more obvious.

Source Routing In SRv6 network, each network element along the message forwarding path has the opportunity to tamper with the SRv6 segment list.

Source Routing at source host Unlike SR-MPLS, SRv6 has a significantly more approachable host implementation. Compared with SR-MPLS, SRv6 is easier to implement on the host side, and the threats are as follows: 1) The attacker generates SRv6 message by obtaining and stealing the identity and real SRH of real users to use unauthorized services. 2) In the process of transmitting SRv6 message from the user host to the operator network, SRH has also been tampered with, including interception/modification/falsification/abuse.

Source Routing from PCC at network ingress Typically, the network operator joins the source routing at the header node of the SRv6 domain, and the source routing may also be tampered with by SRH in the SRv6 management domain.

Source routing across network management domains SRv6 is now typically deployed in only one network management domain and may be deployed in different network domains in the future. In particular, the network elements and threats that have really tampered with the list may be in different network management domains in Operational SRv6 Enabled Networks, causing threats that are difficult to trace. As shown in the figure, suppose that when the network element 1 of SRv6 management domain 1 has tampered with the segment list, but the threat takes effect at SRv6 management domain 2. At this time, the threat generation and effective place are in different network management domains, and the management domain 2 cannot be traced back to the location where the tampering occurred.

Locator Block

Segment Identifiers

SID Compression

SID spoofing

Snooping and Packet Capture

Spoofing

SID lists (IPv6 addresses)

Path enumeration

Infrastructure and topology exposure This seems like a non-issue from a WAN perspective. Needs more thought - could be problematic in a host to host scenario involving a WAN and/or a data center fabric.

Limits in filtering capabilities

Exposure of internal Traffic Engineering paths Existing implementations may contain limited filtering capabilities necessary for proper isolation of the SRH from outside of an SRv6 domain.

Implications on Security Devices SRv6 is commonly used as a tunneling technology in operator networks.To provide VPN service in an SRv6 network, the ingress PE encapsulates the payload with an outer IPv6 header with the SRH carrying the SR Policy segment List along with the VPN service SID.The user traffic towards SRv6 provider backbone will be encapsulated in SRv6 tunnel. When constructing an SRv6 packet, the destination address field of the SRv6 packet changes constantly and the source address field of the SRv6 packet is usually assigned using loopback address (depending on configuration),which will affect the security equipments of the current network.

Hidden Destination Address When an SRv6 packet is forwarded in the SRv6 domain, its destination address changes constantly, the real destination address is hidden. Security devices on SRv6 network may not learn the real destination address and fail to take access control on some SRv6 traffic.

Improper Traffic Filtering The security devices on SRv6 networks need to take care of SRv6 packets. However, the SRv6 packets usually use loopback address of the PE device a as source address. As a result, the address information of SR packets may be asymmetric, resulting in improper filter traffic problems, which affects the effectiveness of security devices. For example, along the forwarding path in SRv6 network, the SR-aware firewall will check the association relationships of the bidirectional VPN traffic packets. And it is able to retrieve the final destination of SRv6 packet from the last entry in the SRH. When 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>, the source address and destination address of the forward and backward VPN traffic are regarded as different flow. Eventually, the legal traffic may be blocked by the firewall.

Emerging technology growing pains

Mitigation Methods This section presents methods that can be used to mitigate the threats and issues that were presented in previous sections. This section does not introduce new security solutions or protocols.

Gap Analysis This section analyzes the security related gaps with respect to the threats and issues that were discussed in the previous sections.

Other considerations

Existing IPv6 Vulnerabilities

Security Considerations TODO Security

IANA Considerations Example non-RFC link

References Normative References 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. Informative References 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. Segment Routing (SR) allows a node to steer a packet flow along any path. Intermediate per-path states are eliminated thanks to source routing. SR Policy is an ordered list of segments (i.e., instructions) that represent a source-routed policy. Packet flows are steered into an SR Policy on a node where it is instantiated called a headend node. The packets steered into an SR Policy carry an ordered list of segments associated with that SR Policy. This document updates RFC 8402 as it details the concepts of SR Policy and steering into an SR Policy. This document specifies version 6 of the Internet Protocol (IPv6). It obsoletes RFC 2460. All RFCs are required to have a Security Considerations section. Historically, such sections have been relatively weak. This document provides guidelines to RFC authors on how to write a good Security Considerations section. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. A DetNet (deterministic network) provides specific performance guarantees to its data flows, such as extremely low data loss rates and bounded latency (including bounded latency variation, i.e., "jitter"). As a result, securing a DetNet requires that in addition to the best practice security measures taken for any mission-critical network, additional security measures may be needed to secure the intended operation of these novel service properties. This document addresses DetNet-specific security considerations from the perspectives of both the DetNet system-level designer and component designer. System considerations include a taxonomy of relevant threats and attacks, and associations of threats versus use cases and service properties. Component-level considerations include ingress filtering and packet arrival-time violation detection. This document also addresses security considerations specific to the IP and MPLS data plane technologies, thereby complementing the Security Considerations sections of those documents. As time and frequency distribution protocols are becoming increasingly common and widely deployed, concern about their exposure to various security threats is increasing. This document defines a set of security requirements for time protocols, focusing on the Precision Time Protocol (PTP) and the Network Time Protocol (NTP). This document also discusses the security impacts of time protocol practices, the performance implications of external security practices on time protocols, and the dependencies between other security services and time synchronization. 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. The ability for a node to specify a forwarding path, other than the normal shortest path, that a particular packet will traverse, benefits a number of network functions. Source-based routing mechanisms have previously been specified for network protocols but have not seen widespread adoption. In this context, the term "source" means "the point at which the explicit route is imposed"; therefore, it is not limited to the originator of the packet (i.e., the node imposing the explicit route may be the ingress node of an operator's network). This document outlines various use cases, with their requirements, that need to be taken into account by the Source Packet Routing in Networking (SPRING) architecture for unicast traffic. Multicast use cases and requirements are out of scope for this document. The functionality provided by IPv6's Type 0 Routing Header can be exploited in order to achieve traffic amplification over a remote path for the purposes of generating denial-of-service traffic. This document updates the IPv6 specification to deprecate the use of IPv6 Type 0 Routing Headers, in light of this security concern. [STANDARDS-TRACK] 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. 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 describes an updated version of the IP Authentication Header (AH), which is designed to provide authentication services in IPv4 and IPv6. This document obsoletes RFC 2402 (November 1998). [STANDARDS-TRACK] This document describes an updated version of the Encapsulating Security Payload (ESP) protocol, which is designed to provide a mix of security services in IPv4 and IPv6. ESP is used to provide confidentiality, data origin authentication, connectionless integrity, an anti-replay service (a form of partial sequence integrity), and limited traffic flow confidentiality. This document obsoletes RFC 2406 (November 1998). [STANDARDS-TRACK] The transition from a pure IPv4 network to a network where IPv4 and IPv6 coexist brings a number of extra security considerations that need to be taken into account when deploying IPv6 and operating the dual-protocol network and the associated transition mechanisms. This document attempts to give an overview of the various issues grouped into three categories: o issues due to the IPv6 protocol itself, o issues due to transition mechanisms, and o issues due to IPv6 deployment. This memo provides information for the Internet community. n.d.

Acknowledgments TODO acknowledge.