| IPPM Working Group | X. Min |
| Internet-Draft | G. Mirsky |
| Intended status: Standards Track | ZTE |
| Expires: January 9, 2020 | L. Bo |
| China Telecom | |
| July 8, 2019 |
Echo Request/Reply for In-situ OAM Capabilities
draft-xiao-ippm-ioam-conf-state-04
This document describes an extension to the echo request/reply mechanisms used in SR-MPLS, SRv6, and SFC environments, which can be used within an IOAM domain, allowing the IOAM encapsulating node to acquire IOAM capabilities of each IOAM transit node and/or IOAM decapsulating node.
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The Data Fields for In-situ OAM (IOAM) [I-D.ietf-ippm-ioam-data] defines data fields for IOAM which records 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 [I-D.ietf-ippm-ioam-data], 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", whereas the device which removes the IOAM data container is referred to as the "IOAM decapsulating node". Nodes within the domain which 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 accurate IOAM data container to the packet, the IOAM encapsulating node needs to know 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.
This document describes an extension to the echo request/reply mechanisms used in SR-MPLS, SRv6, and SFC environments, which can be used within an IOAM domain, allowing the IOAM encapsulating node to acquire 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 SR-MPLS, SRv6, and SFC environments:
The 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.
E2E: Edge to Edge
ICMP: Internet Control Message 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
POSIX: Portable Operating System Interface
POT: Proof of Transit
PTP: Precision Time Protocol
SFC: Service Function Chain
SR-MPLS: Segment Routing with MPLS Data plane
SRv6: Segment Routing with IPv6 Data plane
TTL: Time to Live
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.
In echo request IOAM Capabilities uses TLV (Type-Length-Value tuple) which have the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = IOAM Capabilities | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Namespace-IDs Length | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. List of Namespace-IDs .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: IOAM Capabilities TLV in Echo Request
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 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 TLV. List of Namespace-IDs MAY be included in this TLV of echo request, it means that the IOAM encapsulating node requests only the IOAM capabilities which matches one of the Namespace-IDs. The Namespace-ID has the same definition as what's specified in [I-D.ietf-ippm-ioam-data].
Type is set to the value which indicates that it's an IOAM Capabilities TLV.
Length is the length of the TLV's Value field in octets, Namespace-IDs Length is the Length of the List of Namespace-IDs field in octets.
Value field of this TLV is zero padded to align to a 4-octet boundary.
In echo reply IOAM Capabilities uses TLV which have the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = IOAM Capabilities | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs Length | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. List of Sub-TLVs .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: IOAM Capabilities TLV in Echo Reply
When this TLV is present in the echo reply sent by an IOAM transit node and/or an IOAM decapsulating node, it means that IOAM function is enabled at this node and this TLV contains IOAM capabilities of the sender. List of Sub-TLVs which contain 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 which indicates that it's an IOAM Capabilities TLV.
Length is the length of the TLV's Value field in octets, Sub-TLVs Length is the length of the List of Sub-TLVs field in octets.
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 [I-D.ietf-ippm-ioam-data], five kinds of Sub-TLVs are defined in this document, and in an IOAM Capabilities TLV the same kind of Sub-TLV can appear more times than one with 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.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Sub-type = Pre-allocated trace | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IOAM-Trace-Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Namespace-ID | Egress_MTU |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Egress_if_id (short or wide format) ...... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: IOAM Pre-allocated Tracing Capabilities Sub-TLV
When this sub-TLV is present in the IOAM Capabilities 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 which indicates that it's 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, and 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 4.2 of [I-D.ietf-ippm-ioam-data].
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 4.2 of [I-D.ietf-ippm-ioam-data], it should be a one of the Namespace-IDs listed in the IOAM Capabilities 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.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-type = Incremental trace | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IOAM-Trace-Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Namespace-ID | Egress_MTU |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Egress_if_id (short or wide format) ...... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: IOAM Incremental Tracing Capabilities Sub-TLV
When this sub-TLV is present in the IOAM Capabilities 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 which indicates that it's 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, and 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 4.2 of [I-D.ietf-ippm-ioam-data].
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 4.2 of [I-D.ietf-ippm-ioam-data], it should be a one of the Namespace-IDs listed in the IOAM Capabilities 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.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-type = POT Capabilities | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Namespace-ID | IOAM-POT-Type |P|SoR|Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: IOAM Proof of Transit Capabilities Sub-TLV
When this sub-TLV is present in the IOAM Capabilities 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 which indicates that it's 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 4.3 of [I-D.ietf-ippm-ioam-data], it should be a one of the Namespace-IDs listed in the IOAM Capabilities TLV of echo request.
IOAM-POT-Type field and P bit have the same definition as what's specified in section 4.3 of [I-D.ietf-ippm-ioam-data]. 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, which are specified in section 4.3 of [I-D.ietf-ippm-ioam-data]. This document defines SoR as follow:
Reserved field is reserved for future use and MUST be set to zero.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-type = E2E Capabilities | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Namespace-ID | IOAM-E2E-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|TSF|TSL| Reserved | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: IOAM Edge-to-Edge Capabilities Sub-TLV
When this sub-TLV is present in the IOAM Capabilities 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 which indicates that it's 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 4.4 of [I-D.ietf-ippm-ioam-data], it should be a one of the Namespace-IDs listed in the IOAM Capabilities TLV of echo request.
IOAM-E2E-Type field has the same definition as what's specified in section 4.4 of [I-D.ietf-ippm-ioam-data].
TSF field specifies the timestamp format used by the sending node. This document defines TSF as follow:
TSL field specifies the timestamp length used by the sending node. This document defines TSL as follow:
Reserved field is reserved for future use and MUST be set to zero.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-type = End of Domain | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Namespace-ID | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: IOAM End of Domain Sub-TLV
When this sub-TLV is present in the IOAM Capabilities 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 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 TLV, otherwise the End-of-Domain sub-TLV MUST be present in the IOAM Capabilities TLV sent by the IOAM decapsulating node. Since 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.
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 4.4 of [I-D.ietf-ippm-ioam-data], it should be a one of the Namespace-IDs listed in the IOAM Capabilities TLV of echo request.
Once the IOAM encapsulating node is triggered to acquire IOAM capabilities of each IOAM transit node and/or IOAM decapsulating node, the IOAM encapsulating node will send a batch of echo requests that include the IOAM Capabilities 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, on the analogy of this to increase 1 to TTL every time the IOAM encapsulating node sends a new echo request, until the IOAM encapsulating node receives echo reply sent by the IOAM decapsulating node, which should contain the IOAM Capabilities 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 IOAM capabilities, it can send 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, and 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 TLV will send an echo reply to the IOAM encapsulating node, and within the echo reply, there should be an IOAM Capabilities TLV containing one or more sub-TLVs. The IOAM Capabilities TLV contained in the echo request would be ignored by the receiving node that is unaware of IOAM.
Knowledge of the state of the IOAM domain may be considered confidential. Implementations SHOULD provide a means of filtering the addresses to which echo request/reply may be sent.
This document has no IANA actions.
The authors would like to acknowledge Tianran Zhou for his careful review and helpful comments.
The authors appreciate the f2f discussion with Frank Brockners on this document.