| Internet-Draft | NSH encapsulation for In-situ OAM | May 2023 |
| Brockners & Bhandari | Expires 6 November 2023 | [Page] |
In-situ Operations, Administration, and Maintenance (IOAM) is used for recording and collecting operational and telemetry information while the packet traverses a path between two points in the network. This document outlines how IOAM data fields are encapsulated with the Network Service Header (NSH).¶
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IOAM, as defined in [RFC9197], is used to record and collect OAM information while the packet traverses a particular network domain. The term "in-situ" refers to the fact that the OAM data is added to the data packets rather than is being sent within packets specifically dedicated to OAM. This document defines how IOAM data fields are transported as part of the Network Service Header (NSH) [RFC8300] encapsulation for the Service Function Chaining (SFC) Architecture [RFC7665]. The IOAM-Data-Fields are defined in [RFC9197].¶
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.¶
Abbreviations used in this document:¶
The NSH is defined in [RFC8300]. IOAM-Data-Fields are carried as NSH payload using a next protocol header which follows the NSH headers. An IOAM header is added containing the IOAM-Data-Fields. The IOAM-Data-Fields MUST follow the definitions corresponding to IOAM-Option-Types (e.g., see Section 4 of [RFC9197] and Section 3.2 of [RFC9326]). In an administrative domain where IOAM is used, insertion of the IOAM header in NSH is enabled at the NSH tunnel endpoints, which also serve as IOAM encapsulating/decapsulating nodes by means of configuration. The operator MUST ensure that SFC-aware nodes along the Service Function Path support IOAM, otherwise packets might be dropped (see Section 3 further below, as well as [RFC8300] Section 2.2). The IOAM transit nodes (e.g., an Service Function Forwarder) MUST process all the IOAM headers that are relevant based on its configuration. See [RFC9378] for a discussion of deployment related aspects of IOAM-Data-fields.¶
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+ |Ver|O|U| TTL | Length |U|U|U|U|MD Type| NP = TBD_IOAM | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ N | Service Path Identifier | Service Index | S +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ H | ... | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+ | IOAM-Type | IOAM HDR len | Reserved | Next Protocol | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ I ! | O ! | A ~ IOAM Option and Optional Data Space ~ M | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+ | | | | | Payload + Padding (L2/L3/...) | | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+¶
The NSH header and fields are defined in [RFC8300]. The O-bit MUST be handled following the rules in [I-D.ietf-sfc-oam-packet]. The "NSH Next Protocol" value (referred to as "NP" in the diagram above) is TBD_IOAM.¶
The IOAM related fields in NSH are defined as follows:¶
Multiple IOAM-Option-Types MAY be included within the NSH encapsulation. For example, if a NSH encapsulation contains two IOAM-Option-Types before a data payload, the Next Protocol field of the first IOAM option will contain the value of TBD_IOAM, while the Next Protocol field of the second IOAM-Option-Type will contain the "NSH Next Protocol" number indicating the type of the data payload. The applicability of the IOAM Active and Loopback flags [RFC9322] is outside the scope of this document and may be specified in the future.¶
In case the IOAM Incremental Trace Option-Type is used, an SFC-aware node that serves as an IOAM transit node, needs to adjust the "IOAM HDR Len" field accordingly, see Section 4.4 in [RFC9197].¶
Per Section 2.2 of [RFC8300], packets with Next Protocol values not supported SHOULD be silently dropped by default. Thus, when a packet with IOAM is received at an NSH based forwarding node such as an Service Function Forwarder (SFF) that does not support the IOAM header, it SHOULD drop the packet. The mechanism to maintain and notify of such events are outside the scope of this document.¶
IANA is requested to allocate a code point for IOAM in the "NSH Next Protocol" registry:¶
+---------------+---------------------+---------------+
| Next Protocol | Description | Reference |
+---------------+---------------------+---------------+
| TBD_IOAM | IOAM (Next protocol | This document |
| | is an IOAM header) | |
+---------------+---------------------+---------------+
¶
IOAM is considered a "per domain" feature, where the operator decides on leveraging and configuring IOAM according to the operator's needs. The operator needs to properly secure the IOAM domain to avoid malicious configuration and use, which could include injecting malicious IOAM packets into a domain. For additional IOAM related security considerations, see Section 9 in [RFC9197]. For additional OAM and NSH related security considerations see Section 5 of [I-D.ietf-sfc-oam-packet].¶
The authors would like to thank Eric Vyncke, Nalini Elkins, Srihari Raghavan, Ranganathan T S, Karthik Babu Harichandra Babu, Akshaya Nadahalli, Stefano Previdi, Hemant Singh, Erik Nordmark, LJ Wobker, Andrew Yourtchenko, Greg Mirsky and Mohamed Boucadair for the comments and advice.¶
In addition to editors listed on the title page, the following people have contributed to this document:¶
Vengada Prasad Govindan Cisco Systems, Inc. Email: venggovi@cisco.com¶
Carlos Pignataro Cisco Systems, Inc. 7200-11 Kit Creek Road Research Triangle Park, NC 27709 United States Email: cpignata@cisco.com¶
Hannes Gredler RtBrick Inc. Email: hannes@rtbrick.com¶
John Leddy Email: john@leddy.net¶
Stephen Youell JP Morgan Chase 25 Bank Street London E14 5JP United Kingdom Email: stephen.youell@jpmorgan.com¶
Tal Mizrahi Huawei Network.IO Innovation Lab Israel Email: tal.mizrahi.phd@gmail.com¶
David Mozes Email: mosesster@gmail.com¶
Petr Lapukhov Facebook 1 Hacker Way Menlo Park, CA 94025 US Email: petr@fb.com¶
Remy Chang Barefoot Networks 2185 Park Boulevard Palo Alto, CA 94306 US¶
This section lists several approaches considered for encapsulating IOAM with NSH and presents the rationale for the approach chosen in this document.¶
An encapsulation of IOAM-Data-Fields in NSH should be friendly to an implementation in both hardware as well as software forwarders and support a wide range of deployment cases, including large networks that desire to leverage multiple IOAM-Data-Fields at the same time.¶
Hardware and software friendly implementation: Hardware forwarders benefit from an encapsulation that minimizes iterative look-ups of fields within the packet: Any operation which looks up the value of a field within the packet, based on which another lookup is performed, consumes additional gates and time in an implementation - both of which are desired to be kept to a minimum. This means that flat TLV structures are to be preferred over nested TLV structures. IOAM-Data-Fields are grouped into several categories, including trace, proof-of-transit, and edge-to-edge. Each of these options defines a TLV structure. A hardware-friendly encapsulation approach avoids grouping these three option categories into yet another TLV structure, but would rather carry the options as a serial sequence.¶
Total length of the IOAM-Data-Fields: The total length of IOAM-Data-Fields can grow quite large in case multiple different IOAM-Data-Fields are used and large path-lengths need to be considered. If for example an operator would consider using the IOAM Trace Option-Type and capture node-id, app_data, egress/ingress interface-id, timestamp seconds, timestamps nanoseconds at every hop, then a total of 20 octets would be added to the packet at every hop. In case this particular deployment would have a maximum path length of 15 hops in the IOAM domain, then a maximum of 300 octets were to be encapsulated in the packet.¶
Different approaches for encapsulating IOAM-Data-Fields in NSH could be considered:¶
The third option has been chosen here. This option avoids the additional layer of TLV nesting that the use of NSH MD Type 2 would result in. In addition, this option does not constrain IOAM data to a maximum of 256 octets, thus allowing support for very large deployments.¶