Internet-Draft | Active OAM for SFC | October 2021 |
Mirsky, et al. | Expires 11 April 2022 | [Page] |
A set of requirements for active Operation, Administration, and Maintenance (OAM) of Service Function Chains (SFCs) in a network is presented in this document. Based on these requirements, an encapsulation of active OAM messages in SFC and a mechanism to detect and localize defects are described.¶
This document updates RFC 8300. Particularly, it updates the definition of O (OAM) bit in the Network Service Header (NSH) (RFC 8300) and defines how an active OAM message is identified in the NSH.¶
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[RFC7665] defines data plane elements necessary to implement a Service Function Chaining (SFC). These include:¶
There are different views from different levels of the SFC. One is the service function chain, an entirely abstract view, which defines an ordered set of SFs that must be applied to packets selected based on classification rules. But service function chain doesn't specify the exact mapping between SFFs and SFs. Thus, another logical construct used in SFC is a Service Function Path (SFP). According to [RFC7665], SFP is the instantiation of the SFC in the network and provides a level of indirection between the entirely abstract SFCs and a fully specified ordered list of SFFs and SFs identities that the packet will visit when it traverses the SFC. The latter entity is referred to as Rendered Service Path (RSP). The main difference between SFP and RSP is that the former is the logical construct, while the latter is the realization of the SFP via the sequence of specific SFC data plane elements.¶
This document defines how active Operation, Administration and Maintenance (OAM), per [RFC7799] definition of active OAM, is identified when Network Service Header (NSH) is used as the SFC encapsulation. Following the analysis of SFC OAM in [RFC8924], this document applies and, when necessary, extends requirements listed in Section 4 of [RFC8924] for the use of active OAM in an SFP supporting fault management and performance monitoring. Active OAM tools, conformant to the requirements listed in Section 3, improve, for example, troubleshooting efficiency and defect localization in SFP because they specifically address the architectural principles of NSH. For that purpose, SFC Echo Request and Echo Reply are specified in Section 6. This mechanism enables on-demand Continuity Check, Connectivity Verification, among other operations over SFC in networks, addresses functionalities discussed in Sections 4.1, 4.2, and 4.3 of [RFC8924]. SFC Echo Request and Echo Reply, defined in this document, can be used with encapsulations other than NSH, for example, using MPLS encapsulation, as described in [RFC8595]. The applicability of the SFC Echo Request/Reply mechanism in SFC encapsulations other than NSH is outside the scope of this document. Also, this document updates Section 2.2 of [RFC8300] in part of the definition of O bit in the NSH.¶
The terminology defined in [RFC7665] is used extensively throughout this document, and the reader is expected to be familiar with it.¶
In this document, SFC OAM refers to an active OAM [RFC7799] in an SFC architecture.¶
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.¶
E2E: End-to-End¶
FM: Fault Management¶
NSH: Network Service Header¶
OAM: Operations, Administration, and Maintenance¶
RSP: Rendered Service Path¶
SF: Service Function¶
SFC: Service Function Chain¶
SFF: Service Function Forwarder¶
SFP: Service Function Path¶
MAC: Message Authentication Code¶
As discussed in [RFC8924], SFC-specific means are needed to perform the OAM task of fault management (FM) in an SFC architecture, including failure detection, defect characterization, and localization. This document defines the set of requirements for active FM OAM mechanisms to be used in an SFC architecture.¶
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+ |SFI11| |SFI12| |SFI21| |SFI22| |SFI31| |SFI32| +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ \ / \ / \ / +----------+ +----+ +----+ +----+ |Classifier|---|SFF1|---------|SFF2|----------|SFF3| +----------+ +----+ +----+ +----+
The architecture example depicted in Figure 1 considers a service function chain that includes three distinct service functions. In this example, the SFP traverses SFF1, SFF2, and SFF3. Each SFF is connected to two instances of the same service function. End-to-end (E2E) SFC OAM has the Classifier as the ingress and SFF3 as its egress. Segment SFC OAM is between two elements that are part of the same SFP. Following are the requirements for an FM SFC OAM, whether with the E2E or segment scope:¶
The fate sharing, in the SFC environment, is achieved when a test packet traverses the same path and receives the same treatment in the transport layer as an SFC-encapsulated packet (e.g., NSH).¶
An SFC failure might be declared when several consecutive test packets are not received within a pre-determined time. For example, in the E2E FM SFC OAM case, the egress, SFF3, in the example in Figure 1, could be the entity that detects the SFP's failure by monitoring a flow of periodic test packets. The ingress may be capable of recovering from the failure, e.g., using redundant SFC elements. Thus, it is beneficial for the egress to signal the new defect state to the ingress, which in this example is the Classifier. Hence the following requirement:¶
Once the SFF1 detects the defect, the objective of the SFC OAM changes from the detection of a defect to defect characterization and localization.¶
In the example presented in Figure 1, two distinct instances of the same service function share the same SFF. In this example, the SFP can be realized over several RSPs that use different instances of SF of the same type. For instance, RSP1(SFI11--SFI21--SFI31) and RSP2(SFI12--SFI22--SFI32). Available RSPs can be discovered using the trace function discussed in Section 4.3 [RFC8924] or the procedure defined in Section 6.5.4.¶
The SFC OAM layer model described in [RFC8924] offers an approach for defect localization within a service function chain. As the first step, the SFP's continuity for SFFs that are part of the same SFP could be verified. After the reachability of SFFs has already been verified, SFFs that serve an SF may be used as a test packet source. In such a case, SFF can act as a proxy for another element within the service function chain.¶
The O bit in the NSH is defined in [RFC8300] as follows:¶
This document updates that definition as follows:¶
Active SFC OAM is defined as a combination of OAM commands and/or data included in a message that immediately follows the NSH. To identify the active OAM message, the "Next Protocol" field MUST be set to Active SFC OAM (TBA1) (Section 9.1). The rules for interpreting the values of the O bit and the "Next Protocol" field are as follows:¶
O bit set and the "Next Protocol" value does not match one of identifying active or hybrid OAM protocols (per classification defined in [RFC7799]), e.g., defined in Section 9.1 Active SFC OAM (TBA1).¶
O bit set and the "Next Protocol" value matches one of identifying active or hybrid OAM protocols:¶
O bit is clear:¶
One conclusion from the above-listed rules of processing the O bit and the "Next Protocol" field is to avoid the combination of OAM in an NSH Context Header (Fixed-Length or Variable-Length) and the payload immediately following the NSH because there is no unambiguous way to identify such combination using the O bit and the Next Protocol field.¶
As demonstrated in Section 4 [RFC8924] and Section 3 of this document, SFC OAM is required to perform multiple tasks. Several active OAM protocols could be used to address all the requirements. When IP/UDP encapsulation of an SFC OAM control message is used, protocols can be demultiplexed using the destination UDP port number. But extra IP/UDP headers, especially in an IPv6 network, add noticeable overhead. This document defines Active OAM Header (Figure 2) to demultiplex active OAM protocols on an SFC.¶
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | V | Msg Type | Flags | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ SFC Active OAM Control Packet ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Echo Request/Reply is a well-known active OAM mechanism extensively used to verify a path's continuity, detect inconsistencies between a state in control and the data planes, and localize defects in the data plane. ICMP ([RFC0792] for IPv4 and [RFC4443] for IPv6 networks, respectively) and [RFC8029] are examples of broadly used active OAM protocols based on the Echo Request/Reply principle. The SFC Echo Request/Reply defined in this document addresses several requirements listed in Section 3. Specifically, it can be used to check the continuity of an SFP, trace an SFP, or localize the failure within an SFP. The SFC Echo Request/Reply control message format is presented in Figure 3.¶
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | V | Reserved | Echo Request Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message Type | Reply mode | Return Code |Return Subcode | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sender's Handle | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ TLVs ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The interpretation of the fields is as follows:¶
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 | Reserved | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Value ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
TLV is a variable-length field. Multiple TLVs MAY be placed in an SFC Echo Request/Reply packet. Additional TLVs may be enclosed within a given TLV, subject to the semantics of the (outer) TLV in question. If more than one TLV is to be included, the value of the Type field of the outmost outer TLV MUST be set to "Multiple TLVs Used" (TBA12), as assigned by IANA according to Section 9.4. Figure 4 presents the format of an SFC Echo Request/Reply TLV, where fields are defined as follows:¶
The value of the Return Code field is set to zero by the sender of an Echo Request. The receiver of said Echo Request can set it to one of the values listed in Table 1 in the corresponding Echo Reply that it generates (in cases when the reply is requested).¶
Value | Description |
---|---|
0 | No Return Code |
1 | Malformed Echo Request received |
2 | One or more of the TLVs was not understood |
3 | Authentication failed |
Authentication can be used to protect the integrity of the information in SFC Echo Request and/or Echo Reply. In the [I-D.ietf-sfc-nsh-integrity] a variable-length Context Header has been defined to protect the integrity of the NSH and the payload. The header can also be used for the optional encryption of sensitive metadata. MAC#1 Context Header is more suitable for the integrity protection of active SFC OAM, particularly of the defined in this document SFC Echo Request and Echo Reply. On the other hand, using MAC#2 Context Header allows the detection of mishandling of the O-bit by a transient SFC element.¶
SFC Echo Request control packet MUST use the appropriate transport encapsulation of the monitored SFP. If the NSH is used, Echo Request MUST set O bit, as defined in [RFC8300]. NSH MUST be immediately followed by the SFC Active OAM Header defined in Section 4. The Message Type field's value in the SFC Active OAM Header MUST be set to SFC Echo Request/Echo Reply value (TBA2) per Section 9.2.2.¶
Value of the Reply Mode field MAY be set to:¶
Responder to the SFC Echo Request encapsulates the SFC Echo Reply message in IP/UDP packet if the Reply mode is "Reply via an IPv4/IPv6 UDP Packet". Because the NSH does not identify the ingress node that generated the Echo Request, the source ID MUST be included in the message and used as the IP destination address and destination UDP port number of the SFC Echo Reply. The sender of the SFC Echo Request MUST include an SFC Source TLV (Figure 5).¶
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source ID | Reserved1 | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Port Number | Reserved2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IP Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where¶
A single Source ID TLV for each address family, i.e., IPv4 and IPv6, MAY be present in an SFC Echo Request message. If the Source TLVs for both address families are present in an SFC Echo Request message, the SFF MUST NOT replicate an SFC Echo Reply but choose the destination IP address for the SFC Echo Reply based on the local policy. If more than one Source ID TLV per the address family is present, the receiver MUST use the first TLV and ignore the rest.¶
Punting received SFC Echo Request to the control plane is triggered by one of the following packet processing exceptions: NSH TTL expiration, NSH Service Index (SI) expiration, or the receiver is the terminal SFF for an SFP.¶
Firstly, if the SFC Echo Request is integrity-protected, the receiving SFF first MUST verify the authentication. Then the receiver SFF MUST validate the Source TLV, as defined in Section 6.3.1. Suppose the authentication validation has failed and the Source TLV is considered properly formatted. In that case, the SFF MUST send to the system identified in the Source TLV (see Section 6.5), according to a rate-limit control mechanism, an SFC Echo Reply with the Return Code set to "Authentication failed" and the Subcode set to zero. If the Source TLV is determined malformed, the received SFC Echo Request processing is stopped, the message is dropped, and the event SHOULD be logged, according to a rate-limiting control for logging. Then, the SFF that has received an SFC Echo Request verifies the rest of the received packet's general sanity. If the packet is not well-formed, the receiver SFF SHOULD send an SFC Echo Reply with the Return Code set to "Malformed Echo Request received" and the Subcode set to zero under the control of the rate-limiting mechanism to the system identified in the Source TLV (see Section 6.5). If there are any TLVs that the SFF does not understand, the SFF MUST send an SFC Echo Reply with the Return Code set to 2 ("One or more TLVs was not understood") and set the Subcode to zero. In the latter case, the SFF MAY include an Errored TLVs TLV (Section 6.4.1) that, as sub-TLVs, contains only the misunderstood TLVs. Sender's Handle and Sequence Number fields are not examined but are included in the SFC Echo Reply message. If the sanity check of the received Echo Request succeeded, then the SFF at the end of the SFP MUST set the Return Code value to 5 ("End of the SFP") and the Subcode set to zero. If the SFF is not at the end of the SFP and the TTL value is 1, the value of the Return Code MUST be set to 4 ("TTL Exceeded") and the Subcode set to zero. In all other cases, SFF MUST set the Return Code value to 0 ("No Return Code") and the Subcode set to zero.¶
If the Return Code for the Echo Reply is determined as 2 ("One or more TLVs was not understood"), the Errored TLVs TLV might be included in an Echo Reply. The use of this TLV is meant to inform the sender of an Echo Request of TLVs either not supported by an implementation or parsed and found to be in error.¶
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Errored TLVs | Reserved | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Value | . . . . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where¶
The "Reply Mode" field directs whether and how the Echo Reply message should be sent. The Echo Request sender MAY use TLVs to request that the corresponding Echo Reply be transmitted over the specified path. Section 6.5.1 provides an example of a TLV that specifies the return path of the Echo Reply. Value TBA3 is the "Do not reply" mode and suppresses the Echo Reply packet transmission. The default value (TBA6) for the Reply mode field requests the responder to send the Echo Reply packet out-of-band as IPv4 or IPv6 UDP packet.¶
While SFC Echo Request always traverses the SFP, it is directed to, the corresponding Echo Reply usually is sent over an IP network. There are scenarios when it is beneficial to direct the responder to use a path other than the IP network. This section defines a new Type-Length-Value (TLV), Reply Service Function Path TLV, for Reply via Specified Path mode of SFC Echo Reply.¶
The Reply Service Function Path TLV can provide an efficient mechanism to test SFCs, such as bidirectional and hybrid SFC, as defined in Section 2.2 [RFC7665]. For example, it allows an operator to test both directions of the bidirectional or hybrid SFP with a single SFC Echo Request/Echo Reply operation.¶
The SFC Reply Path TLV carries the information that sufficiently identifies the return SFP that the SFC Echo Reply message is expected to follow. The format of SFC Reply Path TLV is shown in Figure 7.¶
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |SFC Reply Path | Reserved | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reply Service Function Path | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:¶
The format of the Reply Service Function Path field displayed in Figure 8¶
where:¶
[RFC7110] defined mechanism to control return path for MPLS LSP Echo Reply. In SFC's case, the return path is an SFP along which the SFC Echo Reply message MUST be transmitted. Hence, the SFC Reply Path TLV included in the SFC Echo Request message MUST sufficiently identify the SFP that the sender of the Echo Request message expects the receiver to use for the corresponding SFC Echo Reply.¶
When sending an Echo Request, the sender MUST set the value of Reply Mode field to "Reply via Specified Path", defined in Section 6.3, and if the specified path is an SFC path, the Request MUST include SFC Reply Path TLV. The SFC Reply Path TLV consists of the identifier of the reverse SFP and an appropriate Service Index.¶
The Message Authentication Code (MAC) Context Header that is defined in [I-D.ietf-sfc-nsh-integrity] MAY be used to protect the SFC Echo Request's integrity when using the SFC Return Path TLV. If the NSH of the received SFC Echo Request includes the MAC Context Header, the packet's authentication MUST be verified before using any data. If the verification fails, the receiver MUST stop processing the SFC Return Path TLV and MUST send the SFC Echo Reply with the Return Codes value set to the value Authentication failed from the IANA's Return Codes sub-registry of the SFC Echo Request/Echo Reply Parameters registry.¶
The destination SFF of the SFP being tested or the SFF at which SFC TTL expired (as per [RFC8300]) may be sending the Echo Reply. The processing described below equally applies to both cases and is referred to as responding SFF.¶
If the Echo Request message with SFC Reply Path TLV, received by the responding SFF, has Reply Mode value of "Reply via Specified Path" but no SFC Reply Path TLV is present, then the responding SFF MUST send Echo Reply with Return Code set to 6 ("Reply Path TLV is missing"). If the responding SFF cannot find the requested SFP it MUST send Echo Reply with Return Code set to 7 ("Reply SFP was not found") and include the SFC Reply Path TLV from the Echo Request message.¶
Suppose the SFC Echo Request receiver cannot determine whether the specified return path SFP has the route to the initiator. In that case, it SHOULD set the value of the Return Codes field to 8 ("Unverifiable Reply Path"). The receiver MAY drop the Echo Request when it cannot determine whether SFP's return path has the route to the initiator. When sending Echo Request, the sender SHOULD choose a proper source address according to the specified return path SFP to help the receiver find the viable return path.¶
The ability to specify the return path for an Echo Reply might be used in the case of bi-directional SFC. The egress SFF of the forward SFP might not be co-located with a classifier of the reverse SFP, and thus the egress SFF has no information about the reverse path of an SFC. Because of that, even for bi-directional SFC, a reverse SFP needs to be indicated in a Reply Path TLV in the Echo Request message.¶
An SFF SHOULD NOT accept SFC Echo Reply unless the received message passes the following checks:¶
SFC Echo Request/Reply can be used to isolate a defect detected in the SFP and trace an RSP. As for ICMP echo request/reply [RFC0792] and MPLS echo request/reply [RFC8029], this mode is referred to as "traceroute". In the traceroute mode, the sender transmits a sequence of SFC Echo Request messages starting with the NSH TTL value set to 1 and is incremented by 1 in each next Echo Request packet. The sender stops transmitting SFC Echo Request packets when the Return Code in the received Echo Reply equals 5 ("End of the SFP").¶
Suppose a specialized information element (e.g., IPv6 Flow Label [RFC6437] or Flow ID [I-D.ietf-sfc-nsh-tlv]) is used for distributing the load across Equal Cost Multi-Path or Link Aggregation Group paths. In that case, such an element MAY also be used for the SFC OAM traffic. Doing so is meant to control whether the SFC Echo Request follows the same RSP as the monitored flow.¶
The consistency of an SFP can be verified by comparing the view of the SFP from the control or management plane with information collected from traversed by an SFC NSH Echo Request message. Every SFF that receives the Consistency Verification Request (CVReq) MUST perform the following actions:¶
As a result, the ingress SFF collects information about all traversed SFFs and SFs, information on the actual path the CVReq packet has traveled. That information is used to verify the SFC's path consistency. The mechanism for the SFP consistency verification is outside the scope of this document.¶
For the verification of an SFP consistency, two new types of messages to the SFC Echo Request/Reply operation defined in Section 6 with the following values detailed in Table 10:¶
Upon receiving the CVReq, the SFF MUST respond with the Consistency Verification Reply (CVRep). The SFF MUST include the SFs information, as described in Section 6.6.3 and Section 6.6.2.¶
The initiator of CVReq MAY require the collected information in the CVRep be sent in the integrity-protected mode using the Message Authentication Code (MAC) Context Header, defined in [I-D.ietf-sfc-nsh-integrity]. If the NSH of the received SFC Echo Reply includes the MAC Context Header, the authentication of the packet MUST be verified before using any data. If the verification fails, the receiver MUST stop processing the SFF Information Record TLV and notify an operator. Specification of the notification mechanism is outside the scope of this document.¶
For CVReq, the SFF MUST include the Information of SFs into the SF Information Record TLV in the CVRep message. Every SFF sends back a single CVRep message, including information on all the SFs attached to the SFF on the SFP as requested in the CVReq message.¶
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |SFF Record TLV | Reserved | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service Path Identifier (SPI) | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | SF Information Sub-TLV | ~ ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
SFF Information Record TLV is a variable-length TLV that includes the information of all SFFs mapped to the particular SFF instance for the specified SFP. Figure 9 presents the format of an SFC Echo Request/Reply TLV, where fields are defined as the following:¶
Every SFF receiving CVReq packet MUST include the SF characteristic data into the CVRep packet. The data format of an SF sub-TLV, included in a CVRep packet, is displayed in Figure 10.¶
After the CVReq message traverses the SFP, all the information of the SFs on the SFP is collected from the TLVs included in CVRep messages.¶
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |SF sub-TLV| Reserved | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Service Index | SF Type | SF ID Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SF Identifiers | ~ ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
SF sub-TLV Type: Two octets long field. It indicates that the TLV is an SF TLV that contains the information of one SF.¶
Length: Two octets long field. The value of the field is the length of the data following the Length field counted in octets.¶
Service Index: Indicates the SF's position on the SFP.¶
SF Type: Two octets long field. It is defined in [RFC9015] and indicates the type of SF, e.g., Firewall, Deep Packet Inspection, WAN optimization controller, etc.¶
Reserved: For future use. MUST be zeroed on transmission and MUST be ignored on receipt.¶
SF ID Type: One octet-long field with values defined as Section 9.7.¶
SF Identifier: An identifier of the SF. The length of the SF Identifier depends on the type of the SF ID Type. For example, if the SF Identifier is its IPv4 address, the SF Identifier should be 32 bits. SF ID Type and SF Identifier may be a list, of the SFs included in a load balance group.¶
Each SFF in the SFP MUST send one and only one CVRep corresponding to the CVReq. If only one SF is attached to the SFF in such SFP, only one SF information sub-TLV is included in the CVRep. If several SFs attached to the SFF in the SFP, SF Information Sub-TLV MUST be constructed as described below in either Section 6.6.4.1 and Section 6.6.4.2.¶
Multiple SFs attached to the same SFF are the hops of the SFP. The service indexes of these SFs are different. Service function types of these SFs could be different or be the same. Information about all SFs MAY be included in the CVRep message. Information about each SF MUST be listed as separate SF Information Sub-TLVs in the CVRep message.¶
An example of the SFP consistency verification procedure for this case is shown in Figure 11. The Service Function Path(SPI=x) is SF1->SF2->SF4->SF3. The SF1, SF2, and SF3 are attached to SFF1, and SF4 is attached to SFF2. The CVReq message is sent to the SFFs in the sequence of the SFP(SFF1->SFF2->SFF1). Every SFF(SFF1, SFF2) replies with the information of SFs belonging to the SFP. The SF information Sub-TLV in Figure 10 contains information for each SF (SF1, SF2, SF3, and SF4).¶
SF1 SF2 SF4 SF3 +------+------+ | | CVReq ......> SFF1 ......> SFF2 ......> SFF1 (SPI=x) . . . <............ <.......... <........... CVRep1(SF1,SF2) CVRep2(SF4) CVRep3(SF3)
Multiple SFs may be attached to the same SFF to balance the load; in other words, that means that the particular traffic flow will traverse only one of these SFs. These SFs have the same Service Function Type and Service Index. For this case, the SF identifiers and SF ID Type of all these SFs will be listed in the SF Identifiers field and SF ID Type in a single SF information sub-TLV of the CVRep message. The number of these SFs can be calculated using the SF ID Type and the value of the Length field of the sub-TLV.¶
An example of the SFP consistency verification procedure for this case is shown in Figure 12. The Service Function Path (SPI=x) is SF1a/SF1b->SF2a/SF2b. The Service Functions SF1a and SF1b are attached to SFF1, which balances the load among them. The Service Functions SF2a and SF2b are attached to SFF2, which, in turn, balances its load between them. The CVReq message is sent to the SFFs in the sequence of the SFP (i.e. SFF1->SFF2). Every SFF (SFF1, SFF2) replies with the information of SFs belonging to the SFP. The SF information Sub-TLV in Figure 10 contains information for all SFs at that hop.¶
/SF1a /SF2a \SF1b \SF2b | | SFF1 SFF2 CVReq .........> . .........> . (SPI=x) . . <............ <............... CVRep1({SF1a,SF1b}) CVRep2({SF2a,SF2b})
When the integrity protection for SFC active OAM, and SFC Echo Request/Reply in particular, is required, it is RECOMMENDED to use one of the Context Headers defined in [I-D.ietf-sfc-nsh-integrity]. MAC#1 (Message Authentication Code) Context Header could be more suitable for active SFC OAM because it does not require re-calculation of the MAC when the value of the NSH Base Header's TTL field is changed. The integrity protection for SFC active OAM can also be achieved using mechanisms in the underlay data plane. For example, if the underlay is an IPv6 network, IP Authentication Header [RFC4302] or IP Encapsulating Security Payload Header [RFC4303] can be used to provide integrity protection. Confidentiality for the SFC Echo Request/Reply exchanges can be achieved using the IP Encapsulating Security Payload Header [RFC4303]. Also, the security needs for SFC Echo Request/Reply are similar to those of ICMP ping [RFC0792], [RFC4443] and MPLS LSP ping [RFC8029].¶
There are at least three approaches to attacking a node in the overlay network using the mechanisms defined in the document. One is a Denial-of-Service attack, sending an SFC Echo Request to overload an element of the SFC. The second may use spoofing, hijacking, replying, or otherwise tampering with SFC Echo Requests and/or replies to misrepresent, alter the operator's view of the state of the SFC. The third is an unauthorized source using an SFC Echo Request/Reply to obtain information about the SFC and/or its elements, e.g., SFF or SF.¶
It is RECOMMENDED that implementations throttle the SFC ping traffic going to the control plane to mitigate potential Denial-of-Service attacks.¶
Reply and spoofing attacks involving faking or replying to SFC Echo Reply messages would have to match the Sender's Handle and Sequence Number of an outstanding SFC Echo Request message, which is highly unlikely. Thus the non-matching reply would be discarded.¶
To protect against unauthorized sources trying to obtain information about the overlay and/or underlay, an implementation MAY check that the source of the Echo Request is indeed part of the SFP.¶
Also, since Service Function sub-TLV discloses information about the SFP the spoofed CVReq packet may be used to obtain network information, it is RECOMMENDED that implementations provide a means of checking the source addresses of CVReq messages, specified in SFC Source TLV Section 6.3.1, against an access list before accepting the message.¶
The authors greatly appreciate the thorough review and the most helpful comments from Dan Wing, Dirk von Hugo, and Mohamed Boucadair. The authors are thankful to John Drake for his review and the reference to the work on BGP Control Plane for NSH SFC. The authors express their appreciation to Joel M. Halpern for his suggestion about the load-balancing scenario.¶
IANA is requested to assign a new type from the SFC Next Protocol registry as follows:¶
Value | Description | Reference |
---|---|---|
TBA1 | SFC Active OAM | This document |
IANA is requested to create a new SFC Active OAM registry.¶
IANA is requested to create in the SFC Active OAM registry a new sub-registry called "SFC Active OAM Header Version". All code points are assigned according to the "IETF Review" procedure specified in [RFC8126]. The remaining code points to be allocated according to Table 3:¶
Version | Description | Reference |
---|---|---|
Version 0b00 | Protocol as defined by this specification | This document |
Version 0b01 | Unassigned | This document |
Version 0b10 | Unassigned | This document |
Version 0b11 | Unassigned | This document |
IANA is requested to create in the SFC Active OAM registry a new sub-registry called "SFC Active OAM Message Type". All code points in the range 1 through 32767 in this registry shall be allocated according to the "IETF Review" procedure specified in [RFC8126]. The remaining code points to be allocated according to Table 4:¶
Value | Description | Reference |
---|---|---|
0 | Reserved | |
1 - 32767 | Reserved | IETF Consensus |
32768 - 65530 | Reserved | First Come First Served |
65531 - 65534 | Reserved | Private Use |
65535 | Reserved |
IANA is requested to assign a new type from the SFC Active OAM Message Type sub-registry as follows:¶
Value | Description | Reference |
---|---|---|
TBA2 | SFC Echo Request/Echo Reply | This document |
IANA is requested to create in the SFC Active OAM registry the new sub-registry SFC Active OAM Flags.¶
This sub-registry tracks the assignment of 8 flags in the Flags field of the SFC Active OAM Header. The flags are numbered from 0 (most significant bit, transmitted first) to 7.¶
New entries are assigned by Standards Action.¶
Bit Number | Description | Reference |
---|---|---|
7-0 | Unassigned | This document |
IANA is requested to create a new SFC Echo Request/Echo Reply Parameters registry.¶
IANA is requested to create in the SFC Echo Request/Echo Reply Parameters registry a new sub-registry called "SFC Echo Request/Reply Version". All code points assigned according to the "IETF Review" procedure specified in [RFC8126]. The remaining code points to be allocated according to Table 7:¶
Version | Description | Reference |
---|---|---|
Version 0b00 | Protocol as defined by this specification | This document |
Version 0b01 | Unassigned | This document |
Version 0b10 | Unassigned | This document |
Version 0b11 | Unassigned | This document |
IANA is requested to create in the SFC Echo Request/Echo Reply Parameters registry the new sub-registry SFC Echo Request Flags.¶
This sub-registry tracks the assignment of 16 flags in the SFC Echo Request Flags field of the SFC Echo Request message. The flags are numbered from 0 (most significant bit, transmitted first) to 15.¶
New entries are assigned by Standards Action.¶
Bit Number | Description | Reference |
---|---|---|
15-0 | Unassigned | This document |
IANA is requested to create in the SFC Echo Request/Echo Reply Parameters registry the new sub-registry Message Types. All code points in the range 1 through 175 in this registry shall be allocated according to the "IETF Review" procedure specified in [RFC8126]. Code points in the range 176 through 239 in this registry shall be allocated according to the "First Come First Served" procedure specified in [RFC8126]. The remaining code points are allocated as specified in Table 9.¶
Value | Description | Reference |
---|---|---|
0 | Reserved | This document |
1- 175 | Unassigned | This document |
176 - 239 | Unassigned | This document |
240 - 251 | Experimental | This document |
252 - 254 | Private Use | This document |
255 | Reserved | This document |
IANA is requested to assign values as listed in Table 10.¶
Value | Description | Reference |
---|---|---|
TBA3 | SFC Echo Request | This document |
TBA4 | SFC Echo Reply | This document |
TBA16 | SFP Consistency Verification Request | This document |
TBA17 | SFP Consistency Verification Reply | This document |
IANA is requested to create in the SFC Echo Request/Echo Reply Parameters registry the new sub-registry Reply Mode. All code points in the range 1 through 175 in this registry shall be allocated according to the "IETF Review" procedure specified in [RFC8126]. Code points in the range 176 through 239 in this registry shall be allocated according to the "First Come First Served" procedure specified in [RFC8126]. The remaining code points are allocated according to Table 11.¶
Value | Description | Reference |
---|---|---|
0 | Reserved | This document |
1- 175 | Unassigned | This document |
176 - 239 | Unassigned | This document |
240 - 251 | Experimental | This document |
252 - 254 | Private Use | This document |
255 | Reserved | This document |
All code points in the range 1 through 191 in this registry shall be allocated according to the "IETF Review" procedure specified in [RFC8126] and assign values as listed in Table 12.¶
Value | Description | Reference |
---|---|---|
0 | Reserved | |
TBA5 | Do Not Reply | This document |
TBA6 | Reply via an IPv4/IPv6 UDP Packet | This document |
TBA7 | Reply via Application Level Control Channel | This document |
TBA8 | Reply via Specified Path | This document |
TBA9 | Reply via an IPv4/IPv6 UDP Packet with the data integrity protection | This document |
TBA10 | Reply via Application Level Control Channel with the data integrity protection | This document |
TBA11 | Reply via Specified Path with the data integrity protection | This document |
IANA is requested to create in the SFC Echo Request/Echo Reply Parameters registry the new sub-registry Return Codes as described in Table 13.¶
Value | Description | Reference |
---|---|---|
0-191 | Unassigned | IETF Review |
192-251 | Unassigned | First Come First Served |
252-254 | Unassigned | Private Use |
255 | Reserved |
Values defined for the Return Codes sub-registry are listed in Table 14.¶
Value | Description | Reference |
---|---|---|
0 | No Return Code | This document |
1 | Malformed Echo Request received | This document |
2 | One or more of the TLVs was not understood | This document |
3 | Authentication failed | This document |
4 | TTL Exceeded | This document |
5 | End of the SFP | This document |
6 | Reply Path TLV is missing | This document |
7 | Reply SFP was not found | This document |
8 | Unverifiable Reply Path | This document |
IANA is requested to create the SFC Active OAM TLV Type registry. All code points in the range 1 through 175 in this registry shall be allocated according to the "IETF Review" procedure specified in [RFC8126]. Code points in the range 176 through 239 in this registry shall be allocated according to the "First Come First Served" procedure specified in [RFC8126]. The remaining code points are allocated according to Table 15:¶
Value | Description | Reference |
---|---|---|
0 | Reserved | This document |
1- 175 | Unassigned | This document |
176 - 239 | Unassigned | This document |
240 - 251 | Experimental | This document |
252 - 254 | Private Use | This document |
255 | Reserved | This document |
This document defines the following new values in SFC Active OAM TLV Type registry:¶
Value | Description | Reference |
---|---|---|
TBA12 | Multiple TLVs Used | This document |
TBA13 | Source ID TLV | This document |
TBA14 | Errored TLVs | This document |
TBA23 | SFC Reply Path Type | This document |
IANA is requested to assign a new type value from SFC OAM TLV Type registry as follows:¶
Value | Description | Reference |
---|---|---|
TBA18 | SFF Information Record Type | This document |
IANA is requested to assign a new type value from SFC OAM TLV Type registry as follows:¶
Value | Description | Reference |
---|---|---|
TBA19 | SF Information | This document |
IANA is requested to create in the registry SF Types the new sub-registry SF Identifier Types. All code points in the range 1 through 191 in this registry shall be allocated according to the "IETF Review" procedure as specified in [RFC8126] and assign values as follows:¶
Value | Description | Reference |
---|---|---|
0 | Reserved | This document |
TBA20 | IPv4 | This document |
TBA21 | IPv6 | This document |
TBA22 | MAC | This document |
TBA22+1-191 | Unassigned | IETF Review |
192-251 | Unassigned | First Come First Served |
252-254 | Unassigned | Private Use |
255 | Reserved | This document |