opsec F. Gont Internet-Draft EdgeUno Intended status: Informational W. Liu Expires: 4 November 2022 Huawei Technologies 3 May 2022 Recommendations on the Filtering of IPv6 Packets Containing IPv6 Extension Headers at Transit Routers draft-ietf-opsec-ipv6-eh-filtering-10 Abstract This document analyzes the security implications of IPv6 Extension Headers and associated IPv6 options. Additionally, it discusses the operational and interoperability implications of discarding packets based on the IPv6 Extension Headers and IPv6 options they contain. Finally, it provides advice on the filtering of such IPv6 packets at transit routers for traffic not directed to them, for those cases where such filtering is deemed as necessary. 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 4 November 2022. Copyright Notice Copyright (c) 2022 IETF Trust and the persons identified as the document authors. All rights reserved. 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 Gont & Liu Expires 4 November 2022 [Page 1] Internet-Draft Filtering of IPv6 packets with EHs May 2022 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. Terminology and Assumptions Employed in This Document . . . . 4 2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 2.2. Applicability Statement . . . . . . . . . . . . . . . . . 4 2.3. Router Default Behavior and Features . . . . . . . . . . 4 3. IPv6 Extension Headers . . . . . . . . . . . . . . . . . . . 5 3.1. General Discussion . . . . . . . . . . . . . . . . . . . 5 3.2. General Security Implications . . . . . . . . . . . . . . 6 3.3. Rationale for Our Advice on the Handling of IPv6 Packets with Specific IPv6 Extension Headers . . . . . . . . . . 6 3.4. Summary of Advice on the Handling of IPv6 Packets with Specific IPv6 Extension Headers . . . . . . . . . . . . . 6 3.5. Advice on the Handling of IPv6 Packets with Specific IPv6 Extension Headers . . . . . . . . . . . . . . . . . . . . 7 3.6. Advice on the Handling of Packets with Unknown IPv6 Extension Headers . . . . . . . . . . . . . . . . . . . . 16 4. IPv6 Options . . . . . . . . . . . . . . . . . . . . . . . . 17 4.1. General Discussion . . . . . . . . . . . . . . . . . . . 17 4.2. General Security Implications of IPv6 Options . . . . . . 17 4.3. Summary of Advice on the Handling of IPv6 Packets with Specific IPv6 Extension Headers . . . . . . . . . . . . . 18 4.4. Advice on the Handling of Packets with Specific IPv6 Options . . . . . . . . . . . . . . . . . . . . . . . . . 19 4.5. Advice on the handling of Packets with Unknown IPv6 Options . . . . . . . . . . . . . . . . . . . . . . . . . 32 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32 6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 32 7. Security Considerations . . . . . . . . . . . . . . . . . . . 32 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 33 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 33 9.1. Normative References . . . . . . . . . . . . . . . . . . 33 9.2. Informative References . . . . . . . . . . . . . . . . . 37 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 39 1. Introduction IPv6 Extension Headers (EHs) allow for the extension of the IPv6 protocol, and provide support for core functionality such as IPv6 fragmentation. However, common implementation limitations suggest that EHs present a challenge for IPv6 packet routing equipment, particularly when the IPv6 header chain needs to be processed for e.g. enforcing ACLs or implementing other functions [RFC9098]. Gont & Liu Expires 4 November 2022 [Page 2] Internet-Draft Filtering of IPv6 packets with EHs May 2022 Several studies (e.g. [Huston-2022], [I-D.vyncke-v6ops-james], and [RFC7872]) suggest that there is widespread dropping of IPv6 packets that contain IPv6 Extension Headers (EHs). In some cases, such packet drops occur at transit routers. While some operators are known to intentionally drop packets that contain IPv6 EHs, it is possible that some of the measured packet drops are the result of inappropriate advice in this area. This document analyzes both the general security implications of IPv6 EHs, as well as the security implications of specific EH and Option types. It also provides advice on the filtering of IPv6 packets based on the IPv6 EHs and the IPv6 options they contain. Since various protocols may use IPv6 EHs (possibly with IPv6 options), discarding packets based on the IPv6 EHs or IPv6 options they contain can have implications on the proper functioning of such protocols. Thus, this document also attempts to discuss the operational and interoperability implications of such filtering policies. The resulting packet filtering policy typically depends on where in the network such policy is enforced: when the policy is enforced in a transit network, the policy typically follows a "deny-list" approach, where only packets with clear negative implications are dropped. On the other hand, when the policy is enforced closer to the destination systems, the policy typically follows an "accept-list" approach, where only traffic that is expected to be received is allowed. The advice in this document is aimed only at transit routers that may need to enforce a filtering policy based on the EHs and IPv6 options a packet may contain, following a "deny-list" approach, and hence is likely to be much more permissive than a filtering policy to be employed at e.g. the edge of an enterprise network. The advice in this document is meant to improve the current situation of the dropping of packets with IPv6 EHs in the Internet [RFC7872] in such cases where packets are being dropped due to inappropriate or missing guidelines. This document is similar in nature to [RFC7126], which addresses the same problem for the IPv4 case. However, in IPv6, the problem space is compounded by the fact that IPv6 specifies a number of IPv6 EHs, and a number of IPv6 options which may be valid only when included in specific EH types. This document completes and complements the considerations for protecting the control plane from packets containing IP options that can be found in [RFC6192]. Gont & Liu Expires 4 November 2022 [Page 3] Internet-Draft Filtering of IPv6 packets with EHs May 2022 Section 2 specifies the terminology and conventions employed throughout this document. Section 3 discusses IPv6 EHs and provides advice in the area of filtering IPv6 packets that contain such IPv6 EHs. Section 4 discusses IPv6 options and provides advice in the area of filtering IPv6 packets that contain such options. 2. Terminology and Assumptions Employed in This Document 2.1. Terminology The terms "permit" (allow the traffic), "drop" (drop with no notification to sender), and "reject" (drop with appropriate notification to sender) are employed as defined in [RFC3871]. Throughout this document we also employ the term "discard" as a generic term to indicate the act of discarding a packet, irrespective of whether the sender is notified of such drops, and irrespective of whether the specific filtering action is logged. 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. 2.2. Applicability Statement This document provides advice on the filtering of IPv6 packets with EHs at transit routers for traffic not explicitly destined to them, for cases in which such filtering is deemed as necessary. 2.3. Router Default Behavior and Features This document assumes that nodes comply with the requirements in [RFC7045]. Namely, "If a forwarding node discards a packet containing a standard IPv6 extension header, it MUST be the result of a configurable policy and not just the result of a failure to recognise such a header. This means that the discard policy for each standard type of extension header MUST be individually configurable. The default configuration SHOULD allow all standard extension headers." The advice provided in this document is only meant to guide an operator in configuring forwarding devices, and is not to be interpreted as advice regarding default configuration settings for network devices. That is, this document provides advice with respect to operational policies, but does not change the implementation defaults required by [RFC7045]. Gont & Liu Expires 4 November 2022 [Page 4] Internet-Draft Filtering of IPv6 packets with EHs May 2022 We recommend that configuration options are made available to govern the processing of each IPv6 EH type and each IPv6 option type. Such configuration options should include the following possible settings: * Permit this IPv6 EH or IPv6 Option type. * Drop packets containing this IPv6 EH or option type. * Reject packets containing this IPv6 EH or option type (where the packet drop is signaled with an ICMPv6 error message). * Rate-limit traffic containing this IPv6 EH or option type. * Ignore this IPv6 EH or option type (as if it was not present) and process the packet according the rules for the remaining headers. We note that if a packet carries forwarding information (e.g., in an IPv6 Routing Header) this might be an inappropriate or undesirable action. We note that special care needs to be taken when devices log packet drops/rejects. Devices should count the number of packets dropped/ rejected, but the logging of drop/reject events should be limited so as to not overburden device resources. Finally, we note that when discarding packets, it is generally desirable that the sender be signaled of the packet drop, since this is of use for trouble-shooting purposes. However, throughout this document (when recommending that packets be discarded) we generically refer to the action as "discard" without specifying whether the sender is signaled of the packet drop. 3. IPv6 Extension Headers 3.1. General Discussion IPv6 [RFC8200] EHs allow for the extension of the IPv6 protocol. Since both IPv6 EHs and upper-layer protocols share the same namespace ("Next Header" registry/namespace), [RFC7045] identifies which of the currently assigned Internet Protocol numbers identify IPv6 EHs vs. upper-layer protocols. This document discusses the filtering of packets based on the IPv6 EHs (as specified by [RFC7045]) they contain. NOTE: [RFC8200] specifies that non-fragmented IPv6 datagrams and IPv6 First-Fragments must contain the entire IPv6 header chain [RFC7112]. Therefore, intermediate systems can enforce the filtering policies discussed in this document, or resort to simply discarding the offending packets when they fail to comply with the Gont & Liu Expires 4 November 2022 [Page 5] Internet-Draft Filtering of IPv6 packets with EHs May 2022 requirements in [RFC8200]. We note that, in order to implement filtering rules on the fast path, it may be necessary for the filtering device to limit the depth into the packet that can be inspected before giving up. In circumstances where such a limitation exists, it is recommended that implementations provide a configuration option that specifies whether to discard packets if the aforementioned limit is encountered. Operators may then determine according to their own circumstances how such packets will be handled. 3.2. General Security Implications In some device architectures, IPv6 packets that contain IPv6 EHs can cause the corresponding packets to be processed on the slow path, and hence may be leveraged for the purpose of Denial of Service (DoS) attacks [RFC9098] [Cisco-EH] [FW-Benchmark]. Operators are urged to consider the IPv6 EH and IPv6 options handling capabilities of their devices as they make deployment decisions in the future. 3.3. Rationale for Our Advice on the Handling of IPv6 Packets with Specific IPv6 Extension Headers * IPv6 Packets with IPv6 Extension Headers (or options) that are not expected to traverse transit routers should be dropped. * IPv6 Packets with IPv6 Extension Headers (or options) that are only expected to traverse transit routers when a specific technology is employed, should be permitted (or dropped) based on the knowledge regarding the use of such technology in transit provider in question (i.e. permit the packets if the technology is employed, or drop them) * IPv6 Packets with IPv6 Extension Headers (or options) that represent a concrete attack vector to network infrastructure devices should be dropped. * IPv6 packets with any other IPv6 Extension headers (or options) should be permitted. This is an intentional trade-off made to minimize ossification. 3.4. Summary of Advice on the Handling of IPv6 Packets with Specific IPv6 Extension Headers This section summarizes the advice provided in Section 3.5, providing references to the specific sections in which a detailed analysis can be found. Gont & Liu Expires 4 November 2022 [Page 6] Internet-Draft Filtering of IPv6 packets with EHs May 2022 +=========================+==========================+===========+ | EH type | Filtering policy | Reference | +=========================+==========================+===========+ | IPv6 Hop-by-Hop Options | Drop or Ignore | Section | | (Proto=0) | | 3.5.1 | +-------------------------+--------------------------+-----------+ | Routing Header for IPv6 | Drop only RHT0 and RHT1. | Section | | (Proto=43) | Permit other RH Types | 3.5.2 | +-------------------------+--------------------------+-----------+ | Fragment Header for | Permit | Section | | IPv6 (Proto=44) | | 3.5.3 | +-------------------------+--------------------------+-----------+ | Encapsulating Security | Permit | Section | | Payload (Proto=50) | | 3.5.4 | +-------------------------+--------------------------+-----------+ | Authentication Header | Permit | Section | | (Proto=51) | | 3.5.5 | +-------------------------+--------------------------+-----------+ | Destination Options for | Permit | Section | | IPv6 (Proto=60) | | 3.5.6 | +-------------------------+--------------------------+-----------+ | Mobility Header | Permit | Section | | (Proto=135) | | 3.5.7 | +-------------------------+--------------------------+-----------+ | Host Identity Protocol | Permit | Section | | (Proto=139) | | 3.5.8 | +-------------------------+--------------------------+-----------+ | Shim6 Protocol | Permit | Section | | (Proto=140) | | 3.5.9 | +-------------------------+--------------------------+-----------+ | Use for experimentation | Drop | Section | | and testing (Proto=253 | | 3.5.10 | | and 254) | | | +-------------------------+--------------------------+-----------+ Table 1: Summary of Advice on the Handling of IPv6 Packets with Specific IPv6 Extension Headers 3.5. Advice on the Handling of IPv6 Packets with Specific IPv6 Extension Headers 3.5.1. IPv6 Hop-by-Hop Options (Protocol Number=0) Gont & Liu Expires 4 November 2022 [Page 7] Internet-Draft Filtering of IPv6 packets with EHs May 2022 3.5.1.1. Uses The Hop-by-Hop Options header is used to carry optional information that may be examined by every node along a packet's delivery path. It is expected that nodes will examine the Hop-by-Hop Options header if explicitly configured to do so. NOTE: A previous revision of the IPv6 core specification, [RFC2460], originally required that all nodes examined and processed the Hop-by- Hop Options header. However, even before the publication of [RFC8200] a number of implementations already provided the option of ignoring this header unless explicitly configured to examine it. 3.5.1.2. Specification This EH is specified in [RFC8200]. As of May 2022, the following options have been specified for the Hop-by-Hop Options EH: * Type 0x00: Pad1 [RFC8200] * Type 0x01: PadN [RFC8200] * Type 0x05: Router Alert [RFC2711] * Type 0x07: CALIPSO [RFC5570] * Type 0x08: SMF_DPD [RFC6621] * Type 0x23: RPL Option [RFC9008] * Type 0x26: Quick-Start [RFC4782] * Type 0x4D: (Deprecated) * Type 0x63: RPL Option [RFC6553] * Type 0x6D: MPL Option [RFC7731] * Type 0x8A: Endpoint Identification (Deprecated) [draft-ietf-nimrod-eid] * Type 0xC2: Jumbo Payload [RFC2675] * Type 0xEE: IPv6 DFF Header [RFC6971] * Type 0x1E: RFC3692-style Experiment [RFC4727] * Type 0x3E: RFC3692-style Experiment [RFC4727] Gont & Liu Expires 4 November 2022 [Page 8] Internet-Draft Filtering of IPv6 packets with EHs May 2022 * Type 0x5E: RFC3692-style Experiment [RFC4727] * Type 0x7E: RFC3692-style Experiment [RFC4727] * Type 0x9E: RFC3692-style Experiment [RFC4727] * Type 0xBE: RFC3692-style Experiment [RFC4727] * Type 0xDE: RFC3692-style Experiment [RFC4727] * Type 0xFE: RFC3692-style Experiment [RFC4727] 3.5.1.3. Specific Security Implications Legacy nodes that process this extension header might be subject to Denial of Service attacks. NOTE: While [RFC8200] has removed this requirement, the deployed base may still reflect the classical behavior for a while, and hence the potential security problems of this EH are still of concern. 3.5.1.4. Operational and Interoperability Impact if Blocked Discarding packets containing a Hop-by-Hop Options EH would break any of the protocols that rely on it for proper functioning. For example, it would break RSVP [RFC2205] and multicast deployments, and would cause IPv6 jumbograms to be discarded. 3.5.1.5. Advice Nodes implementing [RFC8200] would already ignore this extension header unless explicitly required to process it. For legacy ([RFC2460]) nodes, the recommended configuration for the processing of these packets depends on the features and capabilities of the underlying platform, the configuration of the platform, and also the deployment environment of the platform. On platforms that allow forwarding of packets with HBH Options on the fast path, we recommend that packets with a HBH Options EH be forwarded as normal. Otherwise, on platforms in which processing of packets with a IPv6 HBH Options EH is carried out in the slow path, and an option is provided to rate-limit these packets, we recommend that this option be selected. Finally, when packets containing a HBH Options EH are processed in the slow-path, and the underlying platform does not have any mitigation options available for attacks based on these packets, we recommend that such platforms discard packets containing IPv6 HBH Options EHs. Gont & Liu Expires 4 November 2022 [Page 9] Internet-Draft Filtering of IPv6 packets with EHs May 2022 Finally, we note that RPL (Routing Protocol for Low-Power and Lossy Networks) routers [RFC6550] must not discard packets based on the presence of an IPv6 Hop-by-Hop Options EH, as this would break RPL. 3.5.2. Routing Header for IPv6 (Protocol Number=43) 3.5.2.1. Uses The Routing header is used by an IPv6 source to list one or more intermediate nodes to be "visited" on the way to a packet's destination. 3.5.2.2. Specification This EH is specified in [RFC8200]. [RFC2460] had originally specified the Routing Header Type 0, which was later obsoleted by [RFC5095], and thus removed from [RFC8200]. At of May 2022, the following Routing Types have been specified: * Type 0: Source Route (DEPRECATED) [RFC2460] [RFC5095] * Type 1: Nimrod (DEPRECATED) * Type 2: Type 2 Routing Header [RFC6275] * Type 3: RPL Source Route Header [RFC6554] * Type 4: Segment Routing Header (SRH) [RFC8754] * Types 5-252: Unassigned * Type 253: RFC3692-style Experiment 1 [RFC4727] * Type 254: RFC3692-style Experiment 2 [RFC4727] * Type 255: Reserved 3.5.2.3. Specific Security Implications The security implications of RHT0 have been discussed in detail in [Biondi2007] and [RFC5095]. RHT1 was never widely implemented. The security implications of RHT2, RHT3, and RHT4 (SRH) are discussed in [RFC6275], [RFC6554], and [RFC8754], respectively. Gont & Liu Expires 4 November 2022 [Page 10] Internet-Draft Filtering of IPv6 packets with EHs May 2022 3.5.2.4. Operational and Interoperability Impact if Blocked Blocking packets containing a RHT0 or RHT1 has no operational implications, since both have been deprecated. Blocking packets with a RHT2 would break Mobile IPv6. Packets with a RHT3 may be safely blocked at RPL domain boundaries, since RHT3 headers are employed within a single RPL domain. Blocking packets with a RHT4 (SRH) will break Segment Routing (SR) deployments, if the filtering policy is enforced on packets being forwarded within an SR domain. 3.5.2.5. Advice Intermediate systems should discard packets containing a RHT0, RHT1, or RHT3. Other routing header types should be permitted, as required by [RFC7045]. 3.5.3. Fragment Header for IPv6 (Protocol Number=44) 3.5.3.1. Uses This EH provides the fragmentation functionality for IPv6. 3.5.3.2. Specification This EH is specified in [RFC8200]. 3.5.3.3. Specific Security Implications The security implications of the Fragment Header range from Denial of Service attacks (e.g. based on flooding a target with IPv6 fragments) to information leakage attacks [RFC7739]. 3.5.3.4. Operational and Interoperability Impact if Blocked Blocking packets that contain a Fragment Header will break any protocol that may rely on fragmentation (e.g., the DNS [RFC1034]). However, IP fragmentation is known to introduce fragility to Internet communication [RFC8900]. 3.5.3.5. Advice Intermediate systems should permit packets that contain a Fragment Header. 3.5.4. Encapsulating Security Payload (Protocol Number=50) Gont & Liu Expires 4 November 2022 [Page 11] Internet-Draft Filtering of IPv6 packets with EHs May 2022 3.5.4.1. Uses This EH is employed for the IPsec suite [RFC4303]. 3.5.4.2. Specification This EH is specified in [RFC4303]. 3.5.4.3. Specific Security Implications Besides the general implications of IPv6 EHs, this EH could be employed to potentially perform a DoS attack at the destination system by wasting CPU resources in validating the contents of the packet. 3.5.4.4. Operational and Interoperability Impact if Blocked Discarding packets that employ this EH would break IPsec deployments. 3.5.4.5. Advice Intermediate systems should permit packets containing the Encapsulating Security Payload EH. 3.5.5. Authentication Header (Protocol Number=51) 3.5.5.1. Uses The Authentication Header can be employed for provide authentication services in IPv4 and IPv6. 3.5.5.2. Specification This EH is specified in [RFC4302]. 3.5.5.3. Specific Security Implications Besides the general implications of IPv6 EHs, this EH could be employed to potentially perform a DoS attack at the destination system by wasting CPU resources in validating the contents of the packet. 3.5.5.4. Operational and Interoperability Impact if Blocked Discarding packets that employ this EH would break IPsec deployments. Gont & Liu Expires 4 November 2022 [Page 12] Internet-Draft Filtering of IPv6 packets with EHs May 2022 3.5.5.5. Advice Intermediate systems should permit packets containing an Authentication Header. 3.5.6. Destination Options for IPv6 (Protocol Number=60) 3.5.6.1. Uses The Destination Options header is used to carry optional information that needs be examined only by a packet's destination node(s). 3.5.6.2. Specification This EH is specified in [RFC8200]. As of May 2022, the following options have been specified for this EH: * Type 0x00: Pad1 [RFC8200] * Type 0x01: PadN [RFC8200] * Type 0x04: Tunnel Encapsulation Limit [RFC2473] * Type 0x0F: IPv6 Performance and Diagnostic Metrics (PDM) [RFC8250] * Type 0x4D: (Deprecated) * Type 0xC9: Home Address [RFC6275] * Type 0x8A: Endpoint Identification (Deprecated) [draft-ietf-nimrod-eid] * Type 0x8B: ILNP Nonce [RFC6744] * Type 0x8C: Line-Identification Option [RFC6788] * Type 0x1E: RFC3692-style Experiment [RFC4727] * Type 0x3E: RFC3692-style Experiment [RFC4727] * Type 0x5E: RFC3692-style Experiment [RFC4727] * Type 0x7E: RFC3692-style Experiment [RFC4727] * Type 0x9E: RFC3692-style Experiment [RFC4727] * Type 0xBE: RFC3692-style Experiment [RFC4727] Gont & Liu Expires 4 November 2022 [Page 13] Internet-Draft Filtering of IPv6 packets with EHs May 2022 * Type 0xDE: RFC3692-style Experiment [RFC4727] * Type 0xFE: RFC3692-style Experiment [RFC4727] 3.5.6.3. Specific Security Implications No security implications are known, other than the general implications of IPv6 EHs. For a discussion of possible security implications of specific options specified for the DO header, please see the Section 4.4. 3.5.6.4. Operational and Interoperability Impact if Blocked Discarding packets that contain a Destination Options header would break protocols that rely on this EH type for conveying information, including protocols such as ILNP [RFC6740] and Mobile IPv6 [RFC6275], and IPv6 tunnels that employ the Tunnel Encapsulation Limit option. 3.5.6.5. Advice Intermediate systems should permit packets that contain a Destination Options Header. 3.5.7. Mobility Header (Protocol Number=135) 3.5.7.1. Uses The Mobility Header is an EH used by mobile nodes, correspondent nodes, and home agents in all messaging related to the creation and management of bindings in Mobile IPv6. 3.5.7.2. Specification This EH is specified in [RFC6275]. 3.5.7.3. Specific Security Implications A thorough security assessment of the security implications of the Mobility Header and related mechanisms can be found in Section 15 of [RFC6275]. 3.5.7.4. Operational and Interoperability Impact if Blocked Discarding packets containing this EH would break Mobile IPv6. Gont & Liu Expires 4 November 2022 [Page 14] Internet-Draft Filtering of IPv6 packets with EHs May 2022 3.5.7.5. Advice Intermediate systems should permit packets containing this EH. 3.5.8. Host Identity Protocol (Protocol Number=139) 3.5.8.1. Uses This EH is employed with the Host Identity Protocol (HIP), a protocol that allows consenting hosts to securely establish and maintain shared IP-layer state, allowing separation of the identifier and locator roles of IP addresses, thereby enabling continuity of communications across IP address changes. 3.5.8.2. Specification This EH is specified in [RFC7401]. 3.5.8.3. Specific Security Implications The security implications of the HIP header are discussed in detail in Section 8 of [RFC6275]. 3.5.8.4. Operational and Interoperability Impact if Blocked Discarding packets that contain the Host Identity Protocol would break HIP deployments. 3.5.8.5. Advice Intermediate systems should permit packets that contain a Host Identity Protocol EH. 3.5.9. Shim6 Protocol (Protocol Number=140) 3.5.9.1. Uses This EH is employed by the Shim6 [RFC5533] Protocol. 3.5.9.2. Specification This EH is specified in [RFC5533]. 3.5.9.3. Specific Security Implications The specific security implications are discussed in detail in Section 16 of [RFC5533]. Gont & Liu Expires 4 November 2022 [Page 15] Internet-Draft Filtering of IPv6 packets with EHs May 2022 3.5.9.4. Operational and Interoperability Impact if Blocked Discarding packets that contain this EH will break Shim6. 3.5.9.5. Advice Intermediate systems should permit packets containing this EH. 3.5.10. Use for experimentation and testing (Protocol Numbers=253 and 254) 3.5.10.1. Uses These IPv6 EHs are employed for performing RFC3692-Style experiments (see [RFC3692] for details). 3.5.10.2. Specification These EHs are specified in [RFC3692] and [RFC4727]. 3.5.10.3. Specific Security Implications The security implications of these EHs will depend on their specific use. 3.5.10.4. Operational and Interoperability Impact if Blocked For obvious reasons, discarding packets that contain these EHs limits the ability to perform legitimate experiments across IPv6 routers. 3.5.10.5. Advice Operators should determine according to their own circumstances whether to discard packets containing these EHs. 3.6. Advice on the Handling of Packets with Unknown IPv6 Extension Headers We refer to IPv6 EHs that have not been assigned an Internet Protocol Number by IANA (and marked as such) in [IANA-PROTOCOLS] as "unknown IPv6 extension headers" ("unknown IPv6 EHs"). 3.6.1. Uses New IPv6 EHs may be specified as part of future extensions to the IPv6 protocol. Gont & Liu Expires 4 November 2022 [Page 16] Internet-Draft Filtering of IPv6 packets with EHs May 2022 Since IPv6 EHs and Upper-layer protocols employ the same namespace, it is impossible to tell whether an unknown "Internet Protocol Number" is being employed for an IPv6 EH or an Upper-Layer protocol. 3.6.2. Specification The processing of unknown IPv6 EHs is specified in [RFC7045]. 3.6.3. Specific Security Implications For obvious reasons, it is impossible to determine specific security implications of unknown IPv6 EHs. 3.6.4. Operational and Interoperability Impact if Blocked As noted in [RFC7045], discarding unknown IPv6 EHs may slow down the deployment of new IPv6 EHs and transport protocols. The corresponding IANA registry ([IANA-PROTOCOLS]) should be monitored such that filtering rules are updated as new IPv6 EHs are standardized. We note that since IPv6 EHs and upper-layer protocols share the same numbering space, discarding unknown IPv6 EHs may result in packets encapsulating unknown upper-layer protocols being discarded. 3.6.5. Advice Operators should determine according to their own circumstances whether to discard packets containing unknown IPv6 EHs. 4. IPv6 Options 4.1. General Discussion The following subsections describe specific security implications of different IPv6 options, and provide advice regarding filtering packets that contain such options. 4.2. General Security Implications of IPv6 Options The general security implications of IPv6 options are closely related to those discussed in Section 3.2 for IPv6 EHs. Essentially, packets that contain IPv6 options might need to be processed by an IPv6 router's general-purpose CPU,and hence could present a DDoS risk to that router's general-purpose CPU (and thus to the router itself). For some architectures, a possible mitigation would be to rate-limit the packets that are to be processed by the general-purpose CPU (see e.g. [Cisco-EH]). Gont & Liu Expires 4 November 2022 [Page 17] Internet-Draft Filtering of IPv6 packets with EHs May 2022 4.3. Summary of Advice on the Handling of IPv6 Packets with Specific IPv6 Extension Headers This section summarizes the advice provided in Section 3.5, providing references to the specific sections in which a detailed analysis can be found. +===============================+======================+===========+ | Option | Filtering policy | Reference | +===============================+======================+===========+ | Pad1 (Type=0x00) | Permit | Section | | | | 4.4.1 | +-------------------------------+----------------------+-----------+ | PadN (Type=0x01) | Permit | Section | | | | 4.4.2 | +-------------------------------+----------------------+-----------+ | Tunnel Encapsulation Limit | Permit | Section | | (Type=0x04) | | 4.4.3 | +-------------------------------+----------------------+-----------+ | Router Alert (Type=0x05) | Permit based on | Section | | | needed functionality | 4.4.4 | +-------------------------------+----------------------+-----------+ | CALIPSO (Type=0x07) | Permit based on | Section | | | needed functionality | 4.4.5 | +-------------------------------+----------------------+-----------+ | SMF_DPD (Type=0x08) | Permit based on | Section | | | needed functionality | 4.4.6 | +-------------------------------+----------------------+-----------+ | PDM Option (Type=0x0F) | Permit | Section | | | | 4.4.7 | +-------------------------------+----------------------+-----------+ | RPL Option (Type=0x23) | Permit | Section | | | | 4.4.8 | +-------------------------------+----------------------+-----------+ | Quick-Start (Type=0x26) | Permit | Section | | | | 4.4.9 | +-------------------------------+----------------------+-----------+ | Deprecated (Type=0x4D) | Drop | Section | | | | 4.4.10 | +-------------------------------+----------------------+-----------+ | MPL Option (Type=0x6D) | Permit | Section | | | | 4.4.12 | +-------------------------------+----------------------+-----------+ | Jumbo Payload (Type=0C2) | Permit based on | Section | | | needed functionality | 4.4.16 | +-------------------------------+----------------------+-----------+ | RPL Option (Type=0x63) | Drop in non-RPL | Section | | | routers | 4.4.11 | Gont & Liu Expires 4 November 2022 [Page 18] Internet-Draft Filtering of IPv6 packets with EHs May 2022 +-------------------------------+----------------------+-----------+ | Endpoint Identification | Drop | Section | | (Type=0x8A) | | 4.4.13 | +-------------------------------+----------------------+-----------+ | ILNP Nonce (Type=0x8B) | Permit | Section | | | | 4.4.14 | +-------------------------------+----------------------+-----------+ | Line-Identification Option | Drop | Section | | (Type=0x8C) | | 4.4.15 | +-------------------------------+----------------------+-----------+ | Home Address (Type=0xC9) | Permit | Section | | | | 4.4.17 | +-------------------------------+----------------------+-----------+ | IP_DFF (Type=0xEE) | Permit based on | Section | | | needed functionality | 4.4.18 | +-------------------------------+----------------------+-----------+ | RFC3692-style Experiment | Permit based on | Section | | (Types = 0x1E, 0x3E, 0x5E, | needed functionality | 4.4.19 | | 0x7E, 0x9E, 0xBE, 0xDE, 0xFE) | | | +-------------------------------+----------------------+-----------+ Table 2: Summary of Advice on the Handling of IPv6 Packets with Specific IPv6 options 4.4. Advice on the Handling of Packets with Specific IPv6 Options The following subsections contain a description of each of the IPv6 options that have so far been specified, a summary of the security implications of each of such options, a discussion of possible interoperability implications if packets containing such options are discarded, and specific advice regarding whether packets containing these options should be permitted. 4.4.1. Pad1 (Type=0x00) 4.4.1.1. Uses This option is used when necessary to align subsequent options and to pad out the containing header to a multiple of 8 octets in length. 4.4.1.2. Specification This option is specified in [RFC8200]. 4.4.1.3. Specific Security Implications None. Gont & Liu Expires 4 November 2022 [Page 19] Internet-Draft Filtering of IPv6 packets with EHs May 2022 4.4.1.4. Operational and Interoperability Impact if Blocked Discarding packets that contain this option would potentially break any protocol that relies on IPv6 options. 4.4.1.5. Advice Intermediate systems should not discard packets based on the presence of this option. 4.4.2. PadN (Type=0x01) 4.4.2.1. Uses This option is used when necessary to align subsequent options and to pad out the containing header to a multiple of 8 octets in length. 4.4.2.2. Specification This option is specified in [RFC8200]. 4.4.2.3. Specific Security Implications Because of the possible size of this option, it could be leveraged as a large-bandwidth covert channel. 4.4.2.4. Operational and Interoperability Impact if Blocked Discarding packets that contain this option would potentially break any protocol that relies on IPv6 options. 4.4.2.5. Advice Intermediate systems should not discard IPv6 packets based on the presence of this option. 4.4.3. Tunnel Encapsulation Limit (Type=0x04) 4.4.3.1. Uses The Tunnel Encapsulation Limit option can be employed to specify how many further levels of nesting the packet is permitted to undergo. 4.4.3.2. Specification This option is specified in [RFC2473]. Gont & Liu Expires 4 November 2022 [Page 20] Internet-Draft Filtering of IPv6 packets with EHs May 2022 4.4.3.3. Specific Security Implications Those described in [RFC2473]. 4.4.3.4. Operational and Interoperability Impact if Blocked Discarding packets based on the presence of this option could result in tunnel traffic being discarded. 4.4.3.5. Advice Intermediate systems should not discard packets based on the presence of this option. 4.4.4. Router Alert (Type=0x05) 4.4.4.1. Uses The Router Alert option [RFC2711] is employed by a number of protocols, including the Resource reSerVation Protocol (RSVP) [RFC2205], Multicast Listener Discovery (MLD) [RFC2710] [RFC3810], Multicast Router Discovery (MRD) [RFC4286], and General Internet Signaling Transport (GIST) [RFC5971]. Its usage is discussed in detail in [RFC6398]. 4.4.4.2. Specification This option is specified in [RFC2711]. 4.4.4.3. Specific Security Implications Since this option causes the contents of the packet to be inspected by the handling device, this option could be leveraged for performing DoS attacks. The security implications of the Router Alert option are discussed in detail in [RFC6398]. 4.4.4.4. Operational and Interoperability Impact if Blocked Discarding packets that contain this option would break any protocols that rely on them, such as RSVP and multicast deployments. Please see Section 4.4.4.3 for further details. 4.4.4.5. Advice Packets containing this option should be permitted in environments where support for RSVP, multicast routing, or similar protocols is desired. Gont & Liu Expires 4 November 2022 [Page 21] Internet-Draft Filtering of IPv6 packets with EHs May 2022 4.4.5. CALIPSO (Type=0x07) 4.4.5.1. Uses This option is used for encoding explicit packet Sensitivity Labels on IPv6 packets. It is intended for use only within Multi-Level Secure (MLS) networking environments that are both trusted and trustworthy. 4.4.5.2. Specification This option is specified in [RFC5570]. 4.4.5.3. Specific Security Implications Presence of this option in a packet does not by itself create any specific new threat. Packets with this option ought not normally be seen on the global public Internet. 4.4.5.4. Operational and Interoperability Impact if Blocked If packets with this option are discarded or if the option is stripped from the packet during transmission from source to destination, then the packet itself is likely to be discarded by the receiver because it is not properly labeled. In some cases, the receiver might receive the packet but associate an incorrect sensitivity label with the received data from the packet whose CALIPSO was stripped by a middle-box (such as a packet-scrubber). Associating an incorrect sensitivity label can cause the received information either to be handled as more sensitive than it really is ("upgrading") or as less sensitive than it really is ("downgrading"), either of which is problematic. As noted in [RFC5570], IPsec [RFC4301] [RFC4302] [RFC4303] can be employed to protect the CALIPSO option. 4.4.5.5. Advice Recommendations for handling the CALIPSO option depend on the deployment environment, rather than whether an intermediate system happens to be deployed as a transit device (e.g., IPv6 transit router). Explicit configuration is the only method via which an intermediate system can know whether that particular intermediate system has been deployed within a Multi-Level Secure (MLS) environment. In many cases, ordinary commercial intermediate systems (e.g., IPv6 routers and firewalls) are the majority of the deployed intermediate systems inside an MLS network environment. Gont & Liu Expires 4 November 2022 [Page 22] Internet-Draft Filtering of IPv6 packets with EHs May 2022 For Intermediate systems that DO NOT implement [RFC5570], there should be a configuration option to EITHER (a) drop packets containing the CALIPSO option OR (b) to ignore the presence of the CALIPSO option and forward the packets normally. In non-MLS environments, such intermediate systems should have this configuration option set to (a) above. In MLS environments, such intermediate systems should have this option set to (b) above. The default setting for this configuration option should be set to (a) above, because MLS environments are much less common than non-MLS environments. For Intermediate systems that DO implement [RFC5570], there should be configuration options (a) and (b) from the preceding paragraph and also a third configuration option (c) to process packets containing a CALIPSO option as per [RFC5570]. When deployed in non-MLS environments, such intermediate systems should have this configuration option set to (a) above. When deployed in MLS environments, such intermediate systems should have this set to (c). The default setting for this configuration option MAY be set to (a) above, because MLS environments are much less common than non-MLS environments. 4.4.6. SMF_DPD (Type=0x08) 4.4.6.1. Uses This option is employed in the (experimental) Simplified Multicast Forwarding (SMF) for unique packet identification for IPv6 I-DPD, and as a mechanism to guarantee non-collision of hash values for different packets when H-DPD is used. 4.4.6.2. Specification This option is specified in [RFC6621]. 4.4.6.3. Specific Security Implications None. The use of transient numeric identifiers is subject to the security and privacy considerations discussed in [I-D.irtf-pearg-numeric-ids-generation]. 4.4.6.4. Operational and Interoperability Impact if Blocked Dropping packets containing this option within a MANET domain would break SMF. However, dropping such packets at the border of such domain would have no negative impact. Gont & Liu Expires 4 November 2022 [Page 23] Internet-Draft Filtering of IPv6 packets with EHs May 2022 4.4.6.5. Advice Intermediate systems that are not within a MANET domain should discard packets that contain this option. 4.4.7. PDM (Type=0x0F) 4.4.7.1. Uses This option is employed to convey sequence numbers and timing information in IPv6 packets as a basis for measurements. 4.4.7.2. Specification This option is specified in [RFC8250]. 4.4.7.3. Specific Security Implications Those specified in [RFC8250]. Additionally, since the options employs transient numeric identifiers, implementations may be subject to the issues discussed in [I-D.irtf-pearg-numeric-ids-generation]. 4.4.7.4. Operational and Interoperability Impact if Blocked Dropping packets containing this option will result in negative interoperaiblity implications for traffic employing this option as a basis for measurements. 4.4.7.5. Advice Intermediate systems should not discard packets based on the presence of this option. 4.4.8. RPL Option (Type=0x23) 4.4.8.1. Uses The RPL Option provides a mechanism to include routing information with each datagram that an RPL router forwards. 4.4.8.2. Specification This option is specified in [RFC9008]. 4.4.8.3. Specific Security Implications Those described in [RFC9008]. Gont & Liu Expires 4 November 2022 [Page 24] Internet-Draft Filtering of IPv6 packets with EHs May 2022 4.4.8.4. Operational and Interoperability Impact if Blocked This option can survive outside of an RPL instance. As a result, discarding packets based on the presence of this option would break some use cases for RPL (see [RFC9008]). 4.4.8.5. Advice Intermediate systems should not discard IPv6 packets based on the presence of this option. 4.4.9. Quick-Start (Type=0x26) 4.4.9.1. Uses This IP Option is used in the specification of Quick-Start for TCP and IP, which is an experimental mechanism that allows transport protocols, in cooperation with routers, to determine an allowed sending rate at the start and, at times, in the middle of a data transfer (e.g., after an idle period) [RFC4782]. 4.4.9.2. Specification This option is specified in [RFC4782], on the "Experimental" track. 4.4.9.3. Specific Security Implications Section 9.6 of [RFC4782] notes that Quick-Start is vulnerable to two kinds of attacks: * attacks to increase the routers' processing and state load, and, * attacks with bogus Quick-Start Requests to temporarily tie up available Quick-Start bandwidth, preventing routers from approving Quick-Start Requests from other connections. We note that if routers in a given environment do not implement and enable the Quick-Start mechanism, only the general security implications of IP options (discussed in Section 4.2) would apply. 4.4.9.4. Operational and Interoperability Impact if Blocked The Quick-Start functionality would be disabled, and additional delays in TCP's connection establishment (for example) could be introduced. (Please see Section 4.7.2 of [RFC4782].) We note, however, that Quick-Start has been proposed as a mechanism that could be of use in controlled environments, and not as a mechanism that would be intended or appropriate for ubiquitous deployment in the Gont & Liu Expires 4 November 2022 [Page 25] Internet-Draft Filtering of IPv6 packets with EHs May 2022 global Internet [RFC4782]. 4.4.9.5. Advice Intermediate systems should not discard IPv6 packets based on the presence of this option. 4.4.10. Deprecated (Type=0x4D) 4.4.10.1. Uses No information has been found about this option type. 4.4.10.2. Specification No information has been found about this option type. 4.4.10.3. Specific Security Implications No information has been found about this option type, and hence it has been impossible to perform the corresponding security assessment. 4.4.10.4. Operational and Interoperability Impact if Blocked Unknown. 4.4.10.5. Advice Intermediate systems should discard packets that contain this option. 4.4.11. RPL Option (Type=0x63) 4.4.11.1. Uses The RPL Option provides a mechanism to include routing information with each datagram that an RPL router forwards. 4.4.11.2. Specification This option was originally specified in [RFC6553]. It has been deprecated by [RFC9008]. 4.4.11.3. Specific Security Implications Those described in [RFC9008]. Gont & Liu Expires 4 November 2022 [Page 26] Internet-Draft Filtering of IPv6 packets with EHs May 2022 4.4.11.4. Operational and Interoperability Impact if Blocked This option is meant to be employed within an RPL instance. As a result, discarding packets based on the presence of this option outside of an RPL instance will not result in interoperability implications. 4.4.11.5. Advice Non-RPL routers should discard packets that contain an RPL option. 4.4.12. MPL Option (Type=0x6D) 4.4.12.1. Uses This option is used with the Multicast Protocol for Low power and Lossy Networks (MPL), that provides IPv6 multicast forwarding in constrained networks. 4.4.12.2. Specification This option is specified in [RFC7731], and is meant to be included only in Hop-by-Hop Option headers. 4.4.12.3. Specific Security Implications Those described in [RFC7731]. 4.4.12.4. Operational and Interoperability Impact if Blocked Dropping packets that contain an MPL option within an MPL network would break the Multicast Protocol for Low power and Lossy Networks (MPL). However, dropping such packets at the border of such networks will have no negative impact. 4.4.12.5. Advice Intermediate systems should not discard packets based on the presence of this option. However, since this option has been specified for the Hop-by-Hop Options, such systems should consider the discussion in Section 3.5.1. 4.4.13. Endpoint Identification (Type=0x8A) Gont & Liu Expires 4 November 2022 [Page 27] Internet-Draft Filtering of IPv6 packets with EHs May 2022 4.4.13.1. Uses The Endpoint Identification option was meant to be used with the Nimrod routing architecture [NIMROD-DOC], but has never seen widespread deployment. 4.4.13.2. Specification This option is specified in [NIMROD-DOC]. 4.4.13.3. Specific Security Implications Undetermined. 4.4.13.4. Operational and Interoperability Impact if Blocked None. 4.4.13.5. Advice Intermediate systems should discard packets that contain this option. 4.4.14. ILNP Nonce (Type=0x8B) 4.4.14.1. Uses This option is employed by Identifier-Locator Network Protocol for IPv6 (ILNPv6) for providing protection against off-path attacks for packets when ILNPv6 is in use, and as a signal during initial network-layer session creation that ILNPv6 is proposed for use with this network-layer session, rather than classic IPv6. 4.4.14.2. Specification This option is specified in [RFC6744]. 4.4.14.3. Specific Security Implications Those described in [RFC6744]. 4.4.14.4. Operational and Interoperability Impact if Blocked Discarding packets that contain this option will break INLPv6 deployments. Gont & Liu Expires 4 November 2022 [Page 28] Internet-Draft Filtering of IPv6 packets with EHs May 2022 4.4.14.5. Advice Intermediate systems should not discard packets based on the presence of this option. 4.4.15. Line-Identification Option (Type=0x8C) 4.4.15.1. Uses This option is used by an Edge Router to identify the subscriber premises in scenarios where several subscriber premises may be logically connected to the same interface of an Edge Router. 4.4.15.2. Specification This option is specified in [RFC6788]. 4.4.15.3. Specific Security Implications Those described in [RFC6788]. 4.4.15.4. Operational and Interoperability Impact if Blocked Since this option is meant to be employed in Router Solicitation messages, discarding packets based on the presence of this option at intermediate systems will result in no interoperability implications. 4.4.15.5. Advice Intermediate devices should discard packets that contain this option. 4.4.16. Jumbo Payload (Type=0XC2) 4.4.16.1. Uses The Jumbo payload option provides the means of specifying payloads larger than 65535 bytes. 4.4.16.2. Specification This option is specified in [RFC2675]. 4.4.16.3. Specific Security Implications There are no specific issues arising from this option, except for improper validity checks of the option and associated packet lengths. Gont & Liu Expires 4 November 2022 [Page 29] Internet-Draft Filtering of IPv6 packets with EHs May 2022 4.4.16.4. Operational and Interoperability Impact if Blocked Discarding packets based on the presence of this option will cause IPv6 jumbograms to be discarded. 4.4.16.5. Advice An operator should permit this option only in specific scenarios in which support for IPv6 jumbograms is desired. 4.4.17. Home Address (Type=0xC9) 4.4.17.1. Uses The Home Address option is used by a Mobile IPv6 node while away from home, to inform the recipient of the mobile node's home address. 4.4.17.2. Specification This option is specified in [RFC6275]. 4.4.17.3. Specific Security Implications No (known) additional security implications than those described in [RFC6275]. 4.4.17.4. Operational and Interoperability Impact if Blocked Discarding IPv6 packets based on the presence of this option will break Mobile IPv6. 4.4.17.5. Advice Intermediate systems should not discard IPv6 packets based on the presence of this option. 4.4.18. IP_DFF (Type=0xEE) 4.4.18.1. Uses This option is employed with the (Experimental) Depth-First Forwarding (DFF) in Unreliable Networks. 4.4.18.2. Specification This option is specified in [RFC6971]. Gont & Liu Expires 4 November 2022 [Page 30] Internet-Draft Filtering of IPv6 packets with EHs May 2022 4.4.18.3. Specific Security Implications Those specified in [RFC6971]. 4.4.18.4. Operational and Interoperability Impact if Blocked Dropping packets containing this option within a routing domain that is running DFF would break DFF. However, dropping such packets at the border of such domains will have no security implications. 4.4.18.5. Advice Intermediate systems that do not operate within a routing domain that is running DFF should discard packets containing this option. 4.4.19. RFC3692-style Experiment (Types = 0x1E, 0x3E, 0x5E, 0x7E, 0x9E, 0xBE, 0xDE, 0xFE) 4.4.19.1. Uses These options can be employed for performing RFC3692-style experiments. It is only appropriate to use these values in explicitly configured experiments; they must not be shipped as defaults in implementations. 4.4.19.2. Specification Specified in RFC 4727 [RFC4727] in the context of RFC3692-style experiments. 4.4.19.3. Specific Security Implications The specific security implications will depend on the specific use of these options. 4.4.19.4. Operational and Interoperability Impact if Blocked For obvious reasons, discarding packets that contain these options limits the ability to perform legitimate experiments across IPv6 routers. 4.4.19.5. Advice Operators should determine according to their own circumstances whether to discard packets containing these IPv6 options. Gont & Liu Expires 4 November 2022 [Page 31] Internet-Draft Filtering of IPv6 packets with EHs May 2022 4.5. Advice on the handling of Packets with Unknown IPv6 Options We refer to IPv6 options that have not been assigned an IPv6 option type in the corresponding registry ([IANA-IPV6-PARAM]) as "unknown IPv6 options". 4.5.1. Uses New IPv6 options may be specified as part of future protocol work. 4.5.2. Specification The processing of unknown IPv6 options is specified in [RFC8200]. 4.5.3. Specific Security Implications For obvious reasons, it is impossible to determine specific security implications of unknown IPv6 options. 4.5.4. Operational and Interoperability Impact if Blocked Discarding unknown IPv6 options may slow down the deployment of new IPv6 options. As noted in [draft-gont-6man-ipv6-opt-transmit], the corresponding IANA registry ([IANA-IPV6-PARAM] should be monitored such that IPv6 option filtering rules are updated as new IPv6 options are standardized. 4.5.5. Advice Operators should determine according to their own circumstances whether to discard packets containing unknown IPv6 options. 5. IANA Considerations This document has no actions for IANA. 6. Privacy Considerations There are no privacy considerations associated with this document. 7. Security Considerations This document provides advice on the filtering of IPv6 packets that contain IPv6 EHs (and possibly IPv6 options) at IPv6 transit routers. It is meant to improve the current situation of widespread dropping of such IPv6 packets in those cases where the drops result from improper configuration defaults, or inappropriate advice in this area. Gont & Liu Expires 4 November 2022 [Page 32] Internet-Draft Filtering of IPv6 packets with EHs May 2022 As discussed in Section Section 3.3 of this document, one of the underlying principles for the advice provided in this document is that IPv6 packets with specific EHs or options which may represent an attack vector for infrastructure devices should be dropped. While this policy helps mitigate some specific attack vectors, the recommendations in this document will not help to mitigate vulnerabilities based on implementation errors [RFC9098]. We also note that depending on the router architecture, attempts to filter packets ased on the presence of IPv6 EHs or options might itself represent an attack vector to network infrastructure devices [RFC9098]. 8. Acknowledgements The authors would like to thank Ron Bonica for his work on earlier versions of this document. The authors of this document would like to thank (in alphabetical order) Mikael Abrahamsson, Brian Carpenter, Tim Chown, Roman Danyliw, Darren Dukes, Lars Eggert, David Farmer, Mike Heard, Bob Hinden, Christian Huitema, Benjamin Kaduk, Erik Kline, Murray Kucherawy, Jen Linkova, Carlos Pignataro, Alvaro Retana, Maria Ines Robles, Zaheduzzaman Sarker, Donald Smith, Pascal Thubert, Ole Troan, Gunter Van De Velde, Eric Vyncke, and Robert Wilton, for providing valuable comments on earlier versions of this document. This document borrows some text and analysis from [RFC7126], authored by Fernando Gont, Randall Atkinson, and Carlos Pignataro. The authors would like to thank Warren Kumari and Eric Vyncke for their guidance during the publication process of this document. Fernando would also like to thank Brian Carpenter and Ran Atkinson who, over the years, have answered many questions and provided valuable comments that have benefited his protocol-related work (including the present document). 9. References 9.1. Normative References [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, . Gont & Liu Expires 4 November 2022 [Page 33] Internet-Draft Filtering of IPv6 packets with EHs May 2022 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC2205] Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S. Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification", RFC 2205, DOI 10.17487/RFC2205, September 1997, . [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, December 1998, . [RFC2675] Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms", RFC 2675, DOI 10.17487/RFC2675, August 1999, . [RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast Listener Discovery (MLD) for IPv6", RFC 2710, DOI 10.17487/RFC2710, October 1999, . [RFC2711] Partridge, C. and A. Jackson, "IPv6 Router Alert Option", RFC 2711, DOI 10.17487/RFC2711, October 1999, . [RFC3692] Narten, T., "Assigning Experimental and Testing Numbers Considered Useful", BCP 82, RFC 3692, DOI 10.17487/RFC3692, January 2004, . [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener Discovery Version 2 (MLDv2) for IPv6", RFC 3810, DOI 10.17487/RFC3810, June 2004, . [RFC4286] Haberman, B. and J. Martin, "Multicast Router Discovery", RFC 4286, DOI 10.17487/RFC4286, December 2005, . [RFC4301] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, December 2005, . [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, DOI 10.17487/RFC4302, December 2005, . Gont & Liu Expires 4 November 2022 [Page 34] Internet-Draft Filtering of IPv6 packets with EHs May 2022 [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303, DOI 10.17487/RFC4303, December 2005, . [RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4, ICMPv6, UDP, and TCP Headers", RFC 4727, DOI 10.17487/RFC4727, November 2006, . [RFC4782] Floyd, S., Allman, M., Jain, A., and P. Sarolahti, "Quick- Start for TCP and IP", RFC 4782, DOI 10.17487/RFC4782, January 2007, . [RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation of Type 0 Routing Headers in IPv6", RFC 5095, DOI 10.17487/RFC5095, December 2007, . [RFC5533] Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming Shim Protocol for IPv6", RFC 5533, DOI 10.17487/RFC5533, June 2009, . [RFC5570] StJohns, M., Atkinson, R., and G. Thomas, "Common Architecture Label IPv6 Security Option (CALIPSO)", RFC 5570, DOI 10.17487/RFC5570, July 2009, . [RFC5971] Schulzrinne, H. and R. Hancock, "GIST: General Internet Signalling Transport", RFC 5971, DOI 10.17487/RFC5971, October 2010, . [RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July 2011, . [RFC6398] Le Faucheur, F., Ed., "IP Router Alert Considerations and Usage", BCP 168, RFC 6398, DOI 10.17487/RFC6398, October 2011, . [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, JP., and R. Alexander, "RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks", RFC 6550, DOI 10.17487/RFC6550, March 2012, . Gont & Liu Expires 4 November 2022 [Page 35] Internet-Draft Filtering of IPv6 packets with EHs May 2022 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- Power and Lossy Networks (RPL) Option for Carrying RPL Information in Data-Plane Datagrams", RFC 6553, DOI 10.17487/RFC6553, March 2012, . [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 Routing Header for Source Routes with the Routing Protocol for Low-Power and Lossy Networks (RPL)", RFC 6554, DOI 10.17487/RFC6554, March 2012, . [RFC6621] Macker, J., Ed., "Simplified Multicast Forwarding", RFC 6621, DOI 10.17487/RFC6621, May 2012, . [RFC6740] Atkinson, RJ. and SN. Bhatti, "Identifier-Locator Network Protocol (ILNP) Architectural Description", RFC 6740, DOI 10.17487/RFC6740, November 2012, . [RFC6744] Atkinson, RJ. and SN. Bhatti, "IPv6 Nonce Destination Option for the Identifier-Locator Network Protocol for IPv6 (ILNPv6)", RFC 6744, DOI 10.17487/RFC6744, November 2012, . [RFC6788] Krishnan, S., Kavanagh, A., Varga, B., Ooghe, S., and E. Nordmark, "The Line-Identification Option", RFC 6788, DOI 10.17487/RFC6788, November 2012, . [RFC6971] Herberg, U., Ed., Cardenas, A., Iwao, T., Dow, M., and S. Cespedes, "Depth-First Forwarding (DFF) in Unreliable Networks", RFC 6971, DOI 10.17487/RFC6971, June 2013, . [RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing of IPv6 Extension Headers", RFC 7045, DOI 10.17487/RFC7045, December 2013, . [RFC7112] Gont, F., Manral, V., and R. Bonica, "Implications of Oversized IPv6 Header Chains", RFC 7112, DOI 10.17487/RFC7112, January 2014, . Gont & Liu Expires 4 November 2022 [Page 36] Internet-Draft Filtering of IPv6 packets with EHs May 2022 [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. Henderson, "Host Identity Protocol Version 2 (HIPv2)", RFC 7401, DOI 10.17487/RFC7401, April 2015, . [RFC7731] Hui, J. and R. Kelsey, "Multicast Protocol for Low-Power and Lossy Networks (MPL)", RFC 7731, DOI 10.17487/RFC7731, February 2016, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/RFC8200, July 2017, . [RFC8250] Elkins, N., Hamilton, R., and M. Ackermann, "IPv6 Performance and Diagnostic Metrics (PDM) Destination Option", RFC 8250, DOI 10.17487/RFC8250, September 2017, . [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, . [RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., and F. Gont, "IP Fragmentation Considered Fragile", BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020, . [RFC9008] Robles, M.I., Richardson, M., and P. Thubert, "Using RPI Option Type, Routing Header for Source Routes, and IPv6- in-IPv6 Encapsulation in the RPL Data Plane", RFC 9008, DOI 10.17487/RFC9008, April 2021, . 9.2. Informative References [Biondi2007] Biondi, P. and A. Ebalard, "IPv6 Routing Header Security", CanSecWest 2007 Security Conference, 2007, . Gont & Liu Expires 4 November 2022 [Page 37] Internet-Draft Filtering of IPv6 packets with EHs May 2022 [Cisco-EH] Cisco Systems, "IPv6 Extension Headers Review and Considerations", Whitepaper. October 2006, . [draft-gont-6man-ipv6-opt-transmit] Gont, F., Liu, W., and R. Bonica, "Transmission and Processing of IPv6 Options", IETF Internet Draft, work in progress, August 2014. [draft-ietf-nimrod-eid] Lynn, C.L., "Endpoint Identifier Destination Option", IETF Internet Draft, draft-ietf-nimrod-eid- 00.txt, November 1995. [FW-Benchmark] Zack, E., "Firewall Security Assessment and Benchmarking IPv6 Firewall Load Tests", IPv6 Hackers Meeting #1, Berlin, Germany. June 30, 2013, . [Huston-2022] Huston, G. and J. Damas, "IPv6 Fragmentation and EH Behaviours", IEPG Meeting - March 2022 @ IETF 113, March 2022, . [I-D.irtf-pearg-numeric-ids-generation] Gont, F. and I. Arce, "On the Generation of Transient Numeric Identifiers", Work in Progress, Internet-Draft, draft-irtf-pearg-numeric-ids-generation-08, 31 January 2022, . [I-D.vyncke-v6ops-james] Vyncke, É., Léas, R., and J. Iurman, "Just Another Measurement of Extension header Survivability (JAMES)", Work in Progress, Internet-Draft, draft-vyncke-v6ops- james-01, 19 March 2022, . [IANA-IPV6-PARAM] Internet Assigned Numbers Authority, "Internet Protocol Version 6 (IPv6) Parameters", December 2013, . Gont & Liu Expires 4 November 2022 [Page 38] Internet-Draft Filtering of IPv6 packets with EHs May 2022 [IANA-PROTOCOLS] Internet Assigned Numbers Authority, "Protocol Numbers", 2014, . [NIMROD-DOC] Nimrod Documentation Page, "http://ana-3.lcs.mit.edu/~jnc/nimrod/". [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, December 1998, . [RFC3871] Jones, G., Ed., "Operational Security Requirements for Large Internet Service Provider (ISP) IP Network Infrastructure", RFC 3871, DOI 10.17487/RFC3871, September 2004, . [RFC6192] Dugal, D., Pignataro, C., and R. Dunn, "Protecting the Router Control Plane", RFC 6192, DOI 10.17487/RFC6192, March 2011, . [RFC7126] Gont, F., Atkinson, R., and C. Pignataro, "Recommendations on Filtering of IPv4 Packets Containing IPv4 Options", BCP 186, RFC 7126, DOI 10.17487/RFC7126, February 2014, . [RFC7739] Gont, F., "Security Implications of Predictable Fragment Identification Values", RFC 7739, DOI 10.17487/RFC7739, February 2016, . [RFC7872] Gont, F., Linkova, J., Chown, T., and W. Liu, "Observations on the Dropping of Packets with IPv6 Extension Headers in the Real World", RFC 7872, DOI 10.17487/RFC7872, June 2016, . [RFC9098] Gont, F., Hilliard, N., Doering, G., Kumari, W., Huston, G., and W. Liu, "Operational Implications of IPv6 Packets with Extension Headers", RFC 9098, DOI 10.17487/RFC9098, September 2021, . Authors' Addresses Gont & Liu Expires 4 November 2022 [Page 39] Internet-Draft Filtering of IPv6 packets with EHs May 2022 Fernando Gont EdgeUno Segurola y Habana 4310, 7mo Piso Villa Devoto Ciudad Autonoma de Buenos Aires Argentina Email: fernando.gont@edgeuno.com URI: https://www.edgeuno.com Will (Shucheng) Liu Huawei Technologies Bantian, Longgang District Shenzhen 518129 P.R. China Email: liushucheng@huawei.com Gont & Liu Expires 4 November 2022 [Page 40]