Echo Request/Reply for Enabled In-situ OAM Capabilities

The Data Fields for In-situ OAM (IOAM) defines data fields that record OAM information within the packet while the packet traverses a particular network domain, which is called an IOAM domain. IOAM can be used to complement OAM mechanisms based on, e.g., ICMP or other types of probe packets, and IOAM mechanisms can be leveraged where mechanisms using, e.g., ICMP do not apply or do not offer the desired results. As specified in , within the IOAM-domain, the IOAM data may be updated by network nodes that the packet traverses. The device which adds an IOAM data container to the packet to capture IOAM data is called the "IOAM encapsulating node". In contrast, the device which removes the IOAM data container is referred to as the "IOAM decapsulating node". Nodes within the domain that are aware of IOAM data and read and/or write or process the IOAM data are called "IOAM transit nodes". Both the IOAM encapsulating node and the decapsulating node are referred to as domain edge devices, which can be hosts or network devices. In order to add the correct IOAM data container to the packet, the IOAM encapsulating node needs to know the enabled IOAM capabilities at the IOAM transit nodes and/or the IOAM decapsulating node as a whole, e.g., how many IOAM transit nodes will add tracing data, and what kinds of data fields will be added. A centralized controller could be used in some IOAM deployments. The IOAM encapsulating node can acquire these IOAM capabilities info from the centralized controller, through, e.g., Netconf/Yang, PCEP, or BGP. In the IOAM deployment scenario where there is no centralized controller, Netconf/Yang or IGP may be used for the IOAM encapsulating node to acquire these IOAM capabilities info, however, whether Netconf/Yang or IGP has some limitations as follows. When Netconf/Yang is used in this scenario, each IOAM encapsulating node (including the host when it takes the role of an IOAM encapsulating node) needs to implement a Netconf Client, each IOAM transit node and IOAM decapsulating node (including the host when it takes the role of an IOAM decapsulating node) needs to implement a Netconf Server, the complexity can be an issue. Furthermore, each IOAM encapsulating node needs to establish Netconf Connection with each IOAM transit node and IOAM decapsulating node, the scalability can be an issue. When IGP is used in this scenario, the IGP domain and an IOAM domain don't always have the same coverage. For example, when the IOAM encapsulating node or the IOAM decapsulating node is a host, the availability can be an issue. Furthermore, it might be too challenging to reflect IOAM capabilities at the IOAM transit node and/or the IOAM decapsulating node if these are controlled by a local policy depending on the identity of the IOAM encapsulating node. This document describes an extension to the echo request/reply mechanisms used in IPv6, MPLS and SFC environments, which can be used within an IOAM domain where no Centralized Controller exists, allowing the IOAM encapsulating node to acquire the enabled IOAM capabilities of each IOAM transit node and/or IOAM decapsulating node. The following documents contain references to the echo request/reply mechanisms used in IPv6, MPLS and SFC environments: ("Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification"), ("Extended ICMP to Support Multi-Part Messages") and ("PROBE: A Utility for Probing Interfaces") ("Detecting Multiprotocol Label Switched (MPLS) Data-Plane Failures") ("Active OAM for Service Function Chains in Networks") This feature described in this document is assumedly applied to explicit path (strict or loose), because the precondition for this feature to work is that the echo request reaches each IOAM transit node as live traffic traverses.

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.

BGP: Border Gateway Protocol E2E: Edge to Edge ICMP: Internet Control Message Protocol IGP: Interior Gateway Protocol IOAM: In-situ Operations, Administration, and Maintenance LSP: Label Switched Path MPLS: Multi-Protocol Label Switching MBZ: Must Be Zero MTU: Maximum Transmission Unit NTP: Network Time Protocol OAM: Operations, Administration, and Maintenance PCEP: Path Computation Element (PCE) Communication Protocol POSIX: Portable Operating System Interface POT: Proof of Transit PTP: Precision Time Protocol SFC: Service Function Chain TTL: Time to Live

In echo request IOAM Capabilities Query uses TLV (Type-Length-Value tuple) which have the following format:

When this TLV is present in the echo request sent by an IOAM encapsulating node, it means that the IOAM encapsulating node requests the receiving node to reply with its enabled IOAM capabilities. If there is no IOAM capability to be reported by the receiving node, then this TLV SHOULD be ignored by the receiving node, which means the receiving node SHOULD send echo reply without IOAM capabilities or no echo reply, in the light of whether the echo request includes other TLV than IOAM Capabilities Query TLV. List of Namespace-IDs MAY be included in this TLV of the echo request. In that case, the IOAM encapsulating node requests only the IOAM capabilities that match one of the Namespace-IDs. The Namespace-ID has the same definition as what's specified in . Type is set to the value that identifies it as an IOAM Capabilities Query TLV. Length is the length of the TLV's Value field in octets, including a List of Namespace-IDs. Value field of this TLV is zero-padded to align to a 4-octet boundary.

In echo reply IOAM Capabilities Response uses TLV which have the following format:

When this TLV is present in the echo reply sent by an IOAM transit node and/or an IOAM decapsulating node, it means that the IOAM function is enabled at this node, and this TLV contains the enabled IOAM capabilities of the sender. A list of Sub-TLVs which contains the IOAM capabilities SHOULD be included in this TLV of the echo reply. Note that the IOAM encapsulating node or the IOAM decapsulating node can also be an IOAM transit node. Type is set to the value that identifies it as an IOAM Capabilities Response TLV. Length is the length of the TLV's Value field in octets, including a List of Sub-TLVs. Value field of this TLV or any Sub-TLV is zero-padded to align to a 4-octet boundary. Based on the data fields for IOAM, specified in and , six kinds of Sub-TLVs are defined in this document. The same type of the sub-TLV MAY be in the IOAM Capabilities Response TLV more than once only if with a different Namespace-ID. Note that the IOAM encapsulating node may receive both IOAM Pre-allocated Tracing Capabilities sub-TLV and IOAM Incremental Tracing Capabilities sub-TLV in the process of traceroute, which means both pre-allocated tracing node and incremental tracing node are on the same path, or some node supports both pre-allocated tracing and incremental tracing, the behavior of the IOAM encapsulating node in this scenario is outside the scope of this document.

When this sub-TLV is present in the IOAM Capabilities Response TLV, it means that the sending node is an IOAM transit node and IOAM tracing function is enabled at this IOAM transit node. Sub-type is set to the value that identifies it as an IOAM Pre-allocated Tracing Capabilities sub-TLV. Length is the length of the sub-TLV's Value field in octets. If Egress_if_id is in the short format, which is 16 bits long, it MUST be set to 10. If Egress_if_id is in the wide format, which is 32 bits long, it MUST be set to 12. IOAM-Trace-Type field has the same definition as what's specified in section 5.4 of . Reserved field is reserved for future use and MUST be set to zero. Namespace-ID field has the same definition as what's specified in section 5.3 of , it should be one of the Namespace-IDs listed in the IOAM Capabilities Query TLV of echo request. Egress_MTU field has 16 bits and specifies the MTU of the egress direction out of which the sending node would forward the received echo request, it should be the MTU of the egress interface or the MTU between the sending node and the downstream IOAM transit node. Egress_if_id field has 16 bits (in short format) or 32 bits (in wide format) and specifies the identifier of the egress interface out of which the sending node would forward the received echo request.

When this sub-TLV is present in the IOAM Capabilities Response TLV, it means that the sending node is an IOAM transit node and IOAM tracing function is enabled at this IOAM transit node. Sub-type is set to the value that identifies it as an IOAM Incremental Tracing Capabilities sub-TLV. Length is the length of the sub-TLV's Value field in octets. If Egress_if_id is in the short format, which is 16 bits long, it MUST be set to 10. If Egress_if_id is in the wide format, which is 32 bits long, it MUST be set to 12. IOAM-Trace-Type field has the same definition as what's specified in section 5.4 of . Reserved field is reserved for future use and MUST be set to zero. Namespace-ID field has the same definition as what's specified in section 5.3 of , it should be one of the Namespace-IDs listed in the IOAM Capabilities Query TLV of echo request. Egress_MTU field has 16 bits and specifies the MTU of the egress direction out of which the sending node would forward the received echo request, it should be the MTU of the egress interface or the MTU between the sending node and the downstream IOAM transit node. Egress_if_id field has 16 bits (in short format) or 32 bits (in wide format) and specifies the identifier of the egress interface out of which the sending node would forward the received echo request.

When this sub-TLV is present in the IOAM Capabilities Response TLV, it means that the sending node is an IOAM transit node and IOAM proof of transit function is enabled at this IOAM transit node. Sub-type is set to the value that identifies it as an IOAM Proof of Transit Capabilities sub-TLV. Length is the length of the sub-TLV's Value field in octets and MUST be set to 4. Namespace-ID field has the same definition as what's specified in section 5.3 of , it should be one of the Namespace-IDs listed in the IOAM Capabilities Query TLV of echo request. IOAM-POT-Type field and P bit have the same definition as what's specified in section 5.5 of . If the IOAM encapsulating node receives IOAM-POT-Type and/or P bit values from an IOAM transit node that are different from its own, then the IOAM encapsulating node MAY choose to abandon the proof of transit function or to select one kind of IOAM-POT-Type and P bit, it's based on the policy applied to the IOAM encapsulating node. SoR field has two bits, which means the size of "Random" and "Cumulative" data that are specified in section 5.5 of . This document defines SoR as follow: 0b00 means 64-bit "Random" and 64-bit "Cumulative" data. 0b01~0b11: Reserved for future standardization Reserved field is reserved for future use and MUST be set to zero.

When this sub-TLV is present in the IOAM Capabilities Response TLV, it means that the sending node is an IOAM decapsulating node and IOAM edge-to-edge function is enabled at this IOAM decapsulating node. That is to say, if the IOAM encapsulating node receives this sub-TLV, the IOAM encapsulating node can determine that the node which sends this sub-TLV is an IOAM decapsulating node. Sub-type is set to the value that identifies it as an IOAM Edge-to-Edge Capabilities sub-TLV. Length is the length of the sub-TLV's Value field in octets and MUST be set to 8. Namespace-ID field has the same definition as what's specified in section 5.3 of , it should be one of the Namespace-IDs listed in the IOAM Capabilities Query TLV of echo request. IOAM-E2E-Type field has the same definition as what's specified in section 5.6 of . TSF field specifies the timestamp format used by the sending node. This document defines TSF as follow: 0b00: PTP timestamp format 0b01: NTP timestamp format 0b10: POSIX timestamp format 0b11: Reserved for future standardization TSL field specifies the timestamp length used by the sending node. This document defines TSL as follow. When the TSF field is set to 0b00, which indicates the PTP timestamp format, the values of the TSL field are interpreted as follows: 0b00: 64-bit PTPv1 timestamp as defined in IEEE1588-2008 0b01: 80-bit PTPv2 timestamp as defined in IEEE1588-2008 0b10~0b11: Reserved for future standardization When the TSF field is set to 0b01, which indicates the NTP timestamp format, the values of the TSL field are interpreted as follows: 0b00: 32-bit NTP timestamp as defined in NTPv4 0b01: 64-bit NTP timestamp as defined in NTPv4 0b10: 128-bit NTP timestamp as defined in NTPv4 0b11: Reserved for future standardization When the TSF field is set to 0b10 or 0b11, the TSL field would be ignored. Reserved field is reserved for future use and MUST be set to zero.

When this sub-TLV is present in the IOAM Capabilities Response TLV, it means that the sending node is an IOAM transit node and the IOAM DEX function is enabled at this IOAM transit node. Sub-type is set to the value that identifies it as an IOAM DEX Capabilities sub-TLV. Length is the length of the sub-TLV's Value field in octets and MUST be set to 8. IOAM-Trace-Type field has the same definition as what's specified in section 3.2 of . Namespace-ID field has the same definition as what's specified in section 3.2 of , it should be one of the Namespace-IDs listed in the IOAM Capabilities Query TLV of echo request. Reserved field is reserved for future use and MUST be set to zero.

When this sub-TLV is present in the IOAM Capabilities Response TLV, it means that the sending node is an IOAM decapsulating node. That is to say, if the IOAM encapsulating node receives this sub-TLV, the IOAM encapsulating node can determine that the node which sends this sub-TLV is an IOAM decapsulating node. When the IOAM Edge-to-Edge Capabilities sub-TLV is present in the IOAM Capabilities Response TLV sent by the IOAM decapsulating node, the IOAM End-of-Domain sub-TLV doesn't need to be present in the same IOAM Capabilities Response TLV, otherwise the End-of-Domain sub-TLV MUST be present in the IOAM Capabilities Response TLV sent by the IOAM decapsulating node. Both the IOAM Edge-to-Edge Capabilities sub-TLV and the IOAM End-of-Domain sub-TLV can be used to indicate that the sending node is an IOAM decapsulating node. It's recommended to include only the IOAM Edge-to-Edge Capabilities sub-TLV if IOAM edge-to-edge function is enabled at this IOAM decapsulating node. Sub-type is set to the value that identifies it as an IOAM End of Domain sub-TLV. Length is the length of the sub-TLV's Value field in octets and MUST be set to 4. Namespace-ID field has the same definition as what's specified in section 5.3 of , it should be one of the Namespace-IDs listed in the IOAM Capabilities Query TLV of echo request.

Once the IOAM encapsulating node is triggered to acquire the enabled IOAM capabilities of each IOAM transit node and/or IOAM decapsulating node, the IOAM encapsulating node will send echo requests that include the IOAM Capabilities Query TLV. First with TTL equal to 1 to reach the nearest node, which may be an IOAM transit node or not. Then with TTL equal to 2 to reach the second nearest node, which also may be an IOAM transit node or not. And further, increasing by 1 the TTL every time the IOAM encapsulating node sends a new echo request, until the IOAM encapsulating node receives an echo reply sent by the IOAM decapsulating node, which should contain the IOAM Capabilities Response TLV including the IOAM Edge-to-Edge Capabilities sub-TLV or the IOAM End-of-Domain sub-TLV. Alternatively, if the IOAM encapsulating node knows exactly all the IOAM transit nodes and/or IOAM decapsulating node beforehand, once the IOAM encapsulating node is triggered to acquire the enabled IOAM capabilities, it can send an echo request to each IOAM transit node and/or IOAM decapsulating node directly, without TTL expiration. The IOAM encapsulating node may be triggered by the device administrator, the network management system, the network controller, or even the live user traffic. The specific triggering mechanisms are outside the scope of this document. Each IOAM transit node and/or IOAM decapsulating node that receives an echo request containing the IOAM Capabilities Query TLV will send an echo reply to the IOAM encapsulating node, and within the echo reply, there should be an IOAM Capabilities Response TLV containing one or more sub-TLVs. The IOAM Capabilities Query TLV contained in the echo request would be ignored by the receiving node that is unaware of IOAM.

Queries and responses about the state of an IOAM domain should be processed only from a trusted source. An unauthorized query MUST be discarded by an implementation that supports this specification. Similarly, unsolicited echo response with the IOAM Capabilities TLV MUST be discarded. Authentication of echo request/reply that includes the IOAM Capabilities TLV is one of methods of the integrity protection. Implementations could also provide a means of filtering based on the source address of the received echo request/reply. The integrity protection for IOAM capabilities information collection can also be achieved using mechanisms in the underlay data plane. For example, if the underlay is an IPv6 network, IP Authentication Header or IP Encapsulating Security Payload Header can be used to provide integrity protection. Information about the state of the IOAM domain collected in the IAOM Capabilities TLV is confidential. An implementation can use secure transport to provide privacy protection. For example, if the underlay is an IPv6 network, confidentiality can be achieved using the IP Encapsulating Security Payload Header .

This document requests the following IANA Actions. IANA is requested to create a registry group named "In-Situ OAM (IOAM) Capabilities Parameters". This group will include the following registries: IOAM SoR Capability IOAM TSF+TSL Capability New registries in this group can be created via RFC Required process as per . The subsequent sub-sections detail the registries herein contained. Considering the TLVs/sub-TLVs defined in this document would be carried in different kinds of Echo Request/Reply message, such as ICMPv6 or LSP Ping, it is intended that the registries for Type and sub-Type would be requested in subsequent documents.

This registry defines 4 code points for the IOAM SoR Capability field for identifying the size of "Random" and "Cumulative" data as explained in section 5.5 of . The following code points are defined in this draft:

0b01 - 0b11 are available for assignment via RFC Required process as per .

This registry defines 3 code points for the IOAM TSF Capability field for identifying the timestamp format as explained in section 6 of . When the code point for the IOAM TSF Capability field equals 0b00 which means PTP timestamp format, this registry defines 2 code points for the IOAM TSL Capability field for identifying the timestamp length. When the code point for the IOAM TSF Capability field equals 0b01 which means NTP timestamp format, this registry defines 3 code points for the IOAM TSL Capability field for identifying the timestamp length. The following code points are defined in this draft:

Unassigned code points of TSF+TSL are available for assignment via RFC Required process as per .

The authors would like to acknowledge Tianran Zhou, Dhruv Dhody, Frank Brockners and Cheng Li for their careful review and helpful comments. The authors appreciate the f2f discussion with Frank Brockners on this document. The authors would like to acknowledge Tommy Pauly and Ian Swett for their good suggestion and guidance.