RTGWG Working Group G. Mirsky
Internet-Draft ZTE Corp.
Intended status: Informational August 27, 2019
Expires: February 28, 2020

Identification of Overlay Operations, Administration, and Maintenance (OAM)


This document analyzes how the presence of Operations, Administration, and Maintenance (OAM) control command and/or special data is identified in some overlay networks and an impact on the choice of identification may have on OAM functionality.

Status of This Memo

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Table of Contents

1. Introduction

Operations, Administration, and Maintenance (OAM) protocols are used to detect, localize defects in the network, and monitor network performance. Some OAM functions, e.g., failure detection, work in the network proactively, while others, e.g., defect localization, usually performed on-demand. These tasks achieved by a combination of active, passive, and hybrid OAM methods, as defined in [RFC7799].

This document analyzes how the presence of Operations, Administration, and Maintenance (OAM) control command and/or special data, i.e., OAM packet, is identified in some overlay networks, and an impact the choice of identification may have on OAM functionality of active and hybrid OAM methods for the respective overlay network encapsulation.

2. Conventions used in this document

2.1. Terminology

AMM Alternate Marking method

BIER Bit Indexed Explicit Replication

DetNet Deterministic Networks

GUE Generic UDP Encapsulation

HTS Hybrid Two-step

NSH Network Service Header

NVO3 Network Virtualization Overlays

OAM Operations, Administration and Maintenance

SFC Service Function Chaining

TLV Type-Length-Value

VXLAN-GPE Generic Protocol Extension for VXLAN

ACH Associated Channed Header

Underlay Network or Underlay Layer: The network that provides connectivity between the DetNet nodes. MPLS network that provides LSP connectivity between DetNet nodes is an example of an underlay layer.

2.2. Keywords

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.

3. Overlay Network Encapsulations

New overlay network encapsulations analyzed in two groups:

3.1. Encapsulations with Meta-data

Number of the new encapsulation protocols (e.g., Geneve [I-D.ietf-nvo3-geneve], GUE [I-D.ietf-intarea-gue], and SFC NSH [RFC8300]) support use of Type-Length-Value (TLV) encoding to include optional information into the header. The identification of OAM in these protocols is as the following:

Common between Geneve and NSH is the use of the dedicated flag to identify the OAM packet and, at the same time, the presence of the field that identifies the protocol of the payload that immediately follows after the encapsulation header. [RFC8393] points out that if the value of that field interpreted as none, i.e., no payload follows the header, then OAM may be included in TLVs, thus creating an active OAM packet. The problem with this mechanism to support active OAM methods may be a limitation of the size of data that can be included in a TLV. For example, the maximum size of data in an NSH Meta-data Type 2, as defined in section 2.5.1 [RFC8300], is 512 octets. The maximum length of data in Geneve Option, per section 3.5 [I-D.ietf-nvo3-geneve], is 128 octets. Thus, using one TLV as active OAM packet, would not allow creating test packets of larger size, which is useful when measuring packet loss and latency with synthetic traffic as part of the service activation procedure.

[I-D.ietf-sfc-oam-framework] suggests that the O bit used to identify OAM packet and the Next Protocol field identifies the OAM function:

At the same time, some of in-situ OAM proposals, e.g., [I-D.ietf-sfc-ioam-nsh], suggest using TLV to communicate hybrid OAM commands and data. The proposed resolution of using the combination of O bit and the Next Protocol field:

implies that the O bit only identifies the active OAM packet and not set when hybrid OAM methods used.

3.1.1. Available Solutions

One of the possible solutions for encapsulations with meta-data has been specified in [I-D.ietf-sfc-multi-layer-oam]:

To identify the active OAM message the value on the Next Protocol field MUST be set to Active SFC OAM. The rules of interpreting the values of O bit and the Next Protocol field are as follows:

From the above-listed rules follows the recommendation to avoid the combination of OAM in a Fixed-Length Context Header or Variable- Length Context Header(s) and in the payload immediately following the SFC NSH because there is no unambiguous way to identify such combination using the O bit and the Next Protocol field.

3.2. Fixed-size Encapsulations

Number of the new encapsulation protocols (e.g., VXLAN-GPE [I-D.ietf-nvo3-vxlan-gpe], BIER [RFC8296]) suse fixed-size header. The identification of OAM in these protocols is as the following:

The use of a combination of OAM Flag Bit and the Next Protocol field in VXLAN-GPE requires clarification of the header interpretation when the OAM Flag Bit is set, and the value of the Next Protocol field is one of defined in section 3.2 of [I-D.ietf-nvo3-vxlan-gpe].

BIER encapsulation, defined in [RFC8296], identifies OAM message immediately following the BIER header by the value of the Next Protocol field.

3.3. Source Information Availability

Availability of the packet originator's source information is required for active two-way OAM, e.g., echo request/reply. In cases when the underlay network is IPv4/IPv6 the source information will be derived from the underlay. But when using MPLS underlay network encapsulation of an active OAM packet have to follow specific rules:

3.4. On-path OAM

In addition to active methods, OAM toolset may include methods that don't use specially constructed and injected in the network test packets. [RFC7799] defines OAM methods that are neither entirely active nor passive but are a combination of both as hybrid methods.

One of the examples of the hybrid OAM methods, in-situ OAM, mentioned in Section 3.1. Another example, Alternate Marking method (AMM) [RFC8321], enables on-path OAM functions, e.g., delay and loss measurements, using the data traffic. Because AMM impact on the network can be minimized, measured metrics can be correlated to the network conditions experienced by the specific service. Of all listed in Section 3, BIER allocated the field that may be used for AMM, as discussed in [I-D.ietf-bier-pmmm-oam]. Applicability of AMM to other overlay protocols, i.e., SFC NSH discussed in [I-D.mirsky-sfc-pmamm], Geneve [I-D.fmm-nvo3-pm-alt-mark], and in IPv6 networks [I-D.fioccola-v6ops-ipv6-alt-mark], been actively discussed.

Hybrid Two-step (HTS), defined in [I-D.mirsky-ippm-hybrid-two-step], provides on-path collection and transport of the telemetry information. HTS enables accurate and consistent measurements by separating the measurement action from the transporting data while ensuring that the follow-up packet that carries the telemetry information does follow the data packet that had triggered the measurement.

4. Conclusions

OAM control commands and data may be present as part of the overlay encapsulation header or as a payload that follows the overlay network header. The recommendations:

5. IANA Considerations

This document does not propose any IANA consideration. This section may be removed.

6. Security Considerations

This document lists the OAM requirements for a DetNet domain and does not raise any security concerns or issues in addition to ones common to networking.

7. Acknowledgment


8. References

8.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.

8.2. Informational References

[I-D.fioccola-v6ops-ipv6-alt-mark] Fioccola, G., Velde, G., Cociglio, M. and P. Muley, "IPv6 Performance Measurement with Alternate Marking Method", Internet-Draft draft-fioccola-v6ops-ipv6-alt-mark-01, June 2018.
[I-D.fmm-nvo3-pm-alt-mark] Fioccola, G., Mirsky, G. and T. Mizrahi, "Performance Measurement (PM) with Alternate Marking in Network Virtualization Overlays (NVO3)", Internet-Draft draft-fmm-nvo3-pm-alt-mark-03, October 2018.
[I-D.ietf-bier-pmmm-oam] Mirsky, G., Zheng, L., Chen, M. and G. Fioccola, "Performance Measurement (PM) with Marking Method in Bit Index Explicit Replication (BIER) Layer", Internet-Draft draft-ietf-bier-pmmm-oam-06, July 2019.
[I-D.ietf-intarea-gue] Herbert, T., Yong, L. and O. Zia, "Generic UDP Encapsulation", Internet-Draft draft-ietf-intarea-gue-07, March 2019.
[I-D.ietf-nvo3-geneve] Gross, J., Ganga, I. and T. Sridhar, "Geneve: Generic Network Virtualization Encapsulation", Internet-Draft draft-ietf-nvo3-geneve-13, March 2019.
[I-D.ietf-nvo3-vxlan-gpe] Maino, F., Kreeger, L. and U. Elzur, "Generic Protocol Extension for VXLAN", Internet-Draft draft-ietf-nvo3-vxlan-gpe-07, April 2019.
[I-D.ietf-sfc-ioam-nsh] Brockners, F., Bhandari, S., Govindan, V., Pignataro, C., Gredler, H., Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov, P. and R. Chang, "Network Service Header (NSH) Encapsulation for In-situ OAM (IOAM) Data", Internet-Draft draft-ietf-sfc-ioam-nsh-01, March 2019.
[I-D.ietf-sfc-multi-layer-oam] Mirsky, G., Meng, W., Khasnabish, B. and C. Wang, "Active OAM for Service Function Chains in Networks", Internet-Draft draft-ietf-sfc-multi-layer-oam-03, May 2019.
[I-D.ietf-sfc-oam-framework] Aldrin, S., Pignataro, C., Kumar, N., Krishnan, R. and A. Ghanwani, "Service Function Chaining (SFC) Operations, Administration and Maintenance (OAM) Framework", Internet-Draft draft-ietf-sfc-oam-framework-10, July 2019.
[I-D.mirsky-ippm-hybrid-two-step] Mirsky, G., Lingqiang, W. and G. Zhui, "Hybrid Two-Step Performance Measurement Method", Internet-Draft draft-mirsky-ippm-hybrid-two-step-03, April 2019.
[I-D.mirsky-sfc-pmamm] Mirsky, G., Fioccola, G. and T. Mizrahi, "Performance Measurement (PM) with Alternate Marking Method in Service Function Chaining (SFC) Domain", Internet-Draft draft-mirsky-sfc-pmamm-08, June 2019.
[I-D.mmbb-nvo3-geneve-oam] Mirsky, G., Xiao, M., Boutros, S. and D. Black, "OAM for use in GENEVE", Internet-Draft draft-mmbb-nvo3-geneve-oam-00, July 2019.
[RFC4385] Bryant, S., Swallow, G., Martini, L. and D. McPherson, "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for Use over an MPLS PSN", RFC 4385, DOI 10.17487/RFC4385, February 2006.
[RFC5586] Bocci, M., Vigoureux, M. and S. Bryant, "MPLS Generic Associated Channel", RFC 5586, DOI 10.17487/RFC5586, June 2009.
[RFC7799] Morton, A., "Active and Passive Metrics and Methods (with Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799, May 2016.
[RFC8029] Kompella, K., Swallow, G., Pignataro, C., Kumar, N., Aldrin, S. and M. Chen, "Detecting Multiprotocol Label Switched (MPLS) Data-Plane Failures", RFC 8029, DOI 10.17487/RFC8029, March 2017.
[RFC8296] Wijnands, IJ., Rosen, E., Dolganow, A., Tantsura, J., Aldrin, S. and I. Meilik, "Encapsulation for Bit Index Explicit Replication (BIER) in MPLS and Non-MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January 2018.
[RFC8300] Quinn, P., Elzur, U. and C. Pignataro, "Network Service Header (NSH)", RFC 8300, DOI 10.17487/RFC8300, January 2018.
[RFC8321] Fioccola, G., Capello, A., Cociglio, M., Castaldelli, L., Chen, M., Zheng, L., Mirsky, G. and T. Mizrahi, "Alternate-Marking Method for Passive and Hybrid Performance Monitoring", RFC 8321, DOI 10.17487/RFC8321, January 2018.
[RFC8393] Farrel, A. and J. Drake, "Operating the Network Service Header (NSH) with Next Protocol "None"", RFC 8393, DOI 10.17487/RFC8393, May 2018.

Author's Address

Greg Mirsky ZTE Corp. EMail: gregimirsky@gmail.com