In-situ OAM IPv6 Options

In-situ Operations, Administration, and Maintenance (IOAM) records operational and telemetry information in the packet while the packet traverses a path between two points in the network. This document outlines how IOAM data fields are encapsulated in the IPv6 and discusses deployment options for networks that use IPv6-encapsulated IOAM data fields. These options have distinct deployment considerations; for example, the IOAM domain can either be between hosts, or be between IOAM encapsulating and decapsulating network nodes that forward traffic, such as routers.

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.

Abbreviations used in this document: Edge-to-Edge In-situ Operations, Administration, and Maintenance IOAM Overlay Network Operations, Administration, and Maintenance Proof of Transit

In-situ OAM in IPv6 is used to enhance diagnostics of IPv6 networks. It complements other mechanisms designed to enhance diagnostics of IPv6 networks, such as the IPv6 Performance and Diagnostic Metrics Destination Option described in . IOAM data fields can be encapsulated in “option data” fields using two types of extension headers in IPv6 packets - either Hop-by-Hop Options header or Destination options header. Deployments select one of these extension header types depending on how IOAM is used, as described in section 4 of . Multiple options with the same Option Type MAY appear in the same Hop-by-Hop Options or Destination Options header, with distinct content. In order for IOAM to work in IPv6 networks, IOAM MUST be explicitly enabled per interface on every node within the IOAM domain. Unless a particular interface is explicitly enabled (i.e., explicitly configured) for IOAM, a router MUST drop packets that contain extension headers carrying IOAM data-fields. This is the default behavior and is independent of whether the Hop-by-Hop options or Destination options are used to encode the IOAM data. This ensures that IOAM data does not unintentionally get forwarded outside the IOAM domain. An IPv6 packet carrying IOAM data in an Extension header can have other extension headers, compliant with . IPv6 Hop-by-Hop and Destination Option format for carrying in-situ OAM data fields:

8-bit option type identifier as defined in. 8-bit unsigned integer. Length of this option, in octets, not including the first 2 octets. 8-bit field MUST be set to zero upon transmission and ignored upon reception. 8-bit field as defined in section 7.2 in . Variable-length field. Option-Type-specific data. In-situ OAM Options are inserted as Option data as follows: Pre-allocated Trace Option: The in-situ OAM Preallocated Trace option defined in is represented as an IPv6 option in Hop-by-Hop extension header: 001xxxxx 8-bit identifier of the IOAM type of option. xxxxx=TBD. IOAM Pre-allocated Trace Option Type. Incremental Trace Option: The in-situ OAM Incremental Trace option defined in is represented as an IPv6 option in Hop-by-Hop extension header: 001xxxxx 8-bit identifier of the IOAM type of option. xxxxx=TBD. IOAM Incremental Trace Option Type. Proof of Transit Option: The in-situ OAM POT option defined in is represented as an IPv6 option in Hop-by-Hop extension header: 001xxxxx 8-bit identifier of the IOAM type of option. xxxxx=TBD. IOAM POT Option Type. Edge to Edge Option: The in-situ OAM E2E option defined in is represented as an IPv6 option in Destination extension header: 000xxxxx 8-bit identifier of the IOAM type of option. xxxxx=TBD. IOAM E2E Option Type. All the in-situ OAM IPv6 options defined here have alignment requirements. Specifically, they all require 4n alignment. This ensures that fields specified in are aligned at a multiple-of-4 offset from the start of the Hop-by-Hop and Destination Options header. In addition, to maintain IPv6 extension header 8-octet alignment and avoid the need to add or remove padding at every hop, the Trace-Type for Incremental Trace Option in IPv6 MUST be selected such that the IOAM node data length is a multiple of 8-octets.

IOAM deployments in IPv6 networks should take the following considerations and requirements into account: It is desirable that the addition of IOAM data fields neither changes the way routers forward packets nor the forwarding decisions the routers take. Packets with added OAM information should follow the same path within the domain that an identical packet without OAM information would follow, even in the presence of ECMP. Such behavior is particularly important for deployments where IOAM data fields are only added "on-demand", e.g., to provide further insights in case of undesired network behavior for certain flows. Implementations of IOAM SHOULD ensure that ECMP behavior for packets with and without IOAM data fields is the same. Given that IOAM data fields increase the total size of a packet, the size of a packet including the IOAM data could exceed the PMTU. In particular, the incremental trace IOAM Hop-by-Hop (HbH) Option, which is intended to support hardware implementations of IOAM, changes Option Data Length en-route. Operators of an IOAM domain SHOULD ensure that the addition of OAM information does not lead to fragmentation of the packet, e.g., by configuring the MTU of transit routers and switches to a sufficiently high value. Careful control of the MTU in a network is one of the reasons why IOAM is considered a domain-specific feature (see also ). In addition, the PMTU tolerance range in the IOAM domain should be identified (e.g., through configuration) and IOAM encapsulation operations and/or IOAM data field insertion (in case of incremental tracing) should not be performed if it exceeds the packet size beyond PMTU. Packets with IOAM data or associated ICMP errors, should not arrive at destinations that have no knowledge of IOAM. For exmample, if IOAM is used in in transit devices, misleading ICMP errors due to addition and/or presence of OAM data in a packet could confuse the host that sent the packet if it did not insert the OAM information. OAM data leaks can affect the forwarding behavior and state of network elements outside an IOAM domain. IOAM domains SHOULD provide a mechanism to prevent data leaks or be able to ensure that if a leak occurs, network elements outside the domain are not affected (i.e., they continue to process other valid packets). The source that inserts and leaks the IOAM data needs to be easy to identify for the purpose of troubleshooting, due to the high complexity of troubleshooting a source that inserted the IOAM data and did not remove it when the packet traversed across an Autonomous System (AS). Such a troubleshooting process might require coordination between multiple operators, complex configuration verification, packet capture analysis, etc. Compliance with requires OAM data to be encapsulated instead of header/option insertion directly into in-flight packets using the original IPv6 header.

For deployments where the IOAM domain is bounded by hosts, hosts will perform the operation of IOAM data field encapsulation and decapsulation. IOAM data is carried in IPv6 packets as Hop-by-Hop or Destination options as specified in this document.

For deployments where the IOAM domain is bounded by network devices, network devices such as routers form the edge of an IOAM domain. Network devices will perform the operation of IOAM data field encapsulation and decapsulation.

This section lists out possible deployment options that can be employed to meet the requirements listed in .

The "IPv6-in-IPv6" approach preserves the original IP packet and add an IPv6 header including IOAM data fields in an extension header in front of it, to forward traffic within and across an IOAM domain. The overlay network formed by the additional IPv6 header with the IOAM data fields included in an extension header is referred to as IOAM Overlay Network (ION) in this document. The following steps should be taken to perform an IPv6-in-IPv6 approach: The source address of the outer IPv6 header is that of the IOAM encapsulating node. The destination address of the outer IPv6 header is the same as the inner IPv6 destination address, i.e., the destination address of the packet does not change. To simplify debugging in case of leaked IOAM data fields, consider a new IOAM E2E destination option to identify the Source IOAM domain (AS, v6 prefix). Insert this option into the IOAM destination options EH attached to the outer IPv6 header. This additional information would allow for easy identification of an AS operator that is the source of packets with leaked IOAM information. Note that leaked packets with IOAM data fields would only occur in case a router would be misconfigured. All the IOAM options are defined with type "00" - skip over this option and continue processing the header. Presence of these options must not cause packet drops in network elements that do not understand the option. In addition, should be considered.

The "IP-in-IPv6 encapsulation with ULA" approach can be used to apply IOAM to either an IPv6 or an IPv4 network. In addition, it fulfills requirement C4 (avoid leaks) by using ULA for the ION. Similar to the IPv6-in-IPv6 encapsulation approach above, the original IP packet is preserved. An IPv6 header including IOAM data fields in an extension header is added in front of it, to forward traffic within and across the IOAM domain. IPv6 addresses for the ION, i.e. the outer IPv6 addresses are assigned from the ULA space. Addressing and routing in the ION are to be configured so that the IP-in-IPv6 encapsulated packets follow the same path as the original, non-encapsulated packet would have taken. This would create an internal IPv6 forwarding topology using the IOAM domain's interior ULA address space which is parallel with the forwarding topology that exists with the non-IOAM address space (the topology and address space that would be followed by packets that do not have supplemental IOAM information). Establishment and maintenance of the parallel IOAM ULA forwarding topology could be automated, e.g., similar to how LDP is used in MPLS to establish and maintain an LSP forwarding topology that is parallel to the network's IGP forwarding topology. Transit across the ION could leverage the transit approach for traffic between BGP border routers, as described in , "A.2.3 Encapsulation". Assuming that the operational guidelines specified in Section 4 of are properly followed, the probability of leaks in this approach will be almost close to zero. If the packets do leak through IOAM egress device misconfiguration or partial IOAM egress device failure, the packets' ULA destination address is invalid outside of the IOAM domain. There is no exterior destination to be reached, and the packets will be dropped when they encounter either a router external to the IOAM domain that has a packet filter that drops packets with ULA destinations, or a router that does not have a default route.

In some cases it is desirable to monitor a domain that uses an overlay network that is deployed independently of the need for IOAM, e.g., an overlay network that runs Geneve-in-IPv6, or VXLAN-in-IPv6. In this case IOAM can be encapsulated in as an extension header in the tunnel (outer) IPv6 header. Thus, the tunnel encapsulating node is also the IOAM encapsulating node, and the tunnel end point is also the IOAM decapsulating node.

This document describes the encapsulation of IOAM data fields in IPv6. Security considerations of the specific IOAM data fields for each case (i.e., Trace, Proof of Transit, and E2E) are described and defined in . As this document describes new options for IPv6, these are similar to the security considerations of and the weakness documented in .

This draft requests the following IPv6 Option Type assignments from the Destination Options and Hop-by-Hop Options sub-registry of Internet Protocol Version 6 (IPv6) Parameters. http://www.iana.org/assignments/ipv6-parameters/ipv6- parameters.xhtml#ipv6-parameters-2

The authors would like to thank Tom Herbert, Eric Vyncke, Nalini Elkins, Srihari Raghavan, Ranganathan T S, Karthik Babu Harichandra Babu, Akshaya Nadahalli, Stefano Previdi, Hemant Singh, Erik Nordmark, LJ Wobker, Mark Smith, Andrew Yourtchenko and Justin Iurman for the comments and advice. For the IPv6 encapsulation, this document leverages concepts described in . The authors would like to acknowledge the work done by the author Hiroshi Kitamura and people involved in writing it.