Multi-Layer Active OAM for Service Function Chains in Networks

defines components necessary to implement Service Function Chain (SFC). These include a classifier which performs classification of incoming packets. A Service Function Forwarder (SFF) is responsible for forwarding traffic to one or more connected Service Functions (SFs) according to the information carried in the SFC encapsulation. SFF also handles traffic coming back from the SF and transports the data packets to the next SFF. And the SFF serves as termination element of the Service Function Path (SFP). SF is responsible for specific treatment of received packets. Resulting from that SFC is constructed by a number of these components, there are different views from different levels of the SFC. One is the SFC, fully abstract entity, that defines an ordered set of SFs that must be applied to packets selected as a result of classification. But SFC doesn't define exact mapping between SFFs and SFs. Thus there exists another semi-abstract entity referred as SFP. SFP is the instantiation of the SFC in the network and provides a level of indirection between the fully abstract SFC 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 being referred as Rendered Service Path (RSP). The main difference between SFP and RSP is that in the former the authority to select the SFF/SF has been delegated to the network. This document proposes the multi-layer model of SFC active Operation, Administration and Maintenance (OAM), per definition of active OAM, lists requirements to improve the troubleshooting efficiency and defines SFC Echo request and Echo reply that enables on-demand Continuity Check, Connectivity Verification among other operations over SFC in networks.

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.

Unless explicitly specified in this document, active OAM in SFC and SFC OAM are being used interchangeably. e2e: End-to-End FM: Fault Management NSH: Network Service Header OAM: Operations, Administration, and Maintenance RDI: Remote Defect Indication RSP: Rendered Service Path SF: Service Function SFC: Service Function Chain SFF: Service Function Forwarder SFP: Service Function Path

As described in , multiple layers come into play to realize the SFC, including the Service layer, the underlying Network layer, as well as the Link layer, which are depicted in : The Service layer consists of classifiers and/or service functions/SFs. Network and Transport layers leverage various overlay network technologies interconnecting SFs to establish SFP. The Link layer is technology specific and reflects the technology used in the underlay network.

To perform the OAM task of fault management (FM) in an SFC, that includes failure detection, defect characterization and localization, this document defines the multi-layer model of OAM, presented in , and set of requirements towards active OAM mechanisms to be used on an SFC. In example presented in the service SFP1 may be realized through two RSPs, RSP1(SF1--SF3--SF5) and RSP2(SF2--SF4--SF6). To perform end-to-end (e2e) FM SFC OAM: REQ#1: Packets of active OAM in SFC SHOULD be fate sharing with data traffic, i.e. in-band with the monitored traffic, i.e. follow exactly the same RSP, in forward direction, i.e. from ingress toward egress end point(s) of the OAM test. REQ#2: SFC OAM MUST support pro-active monitoring of any element in the SFC availability. The egress, SFF3 in example in , is the entity that detects the failure of the SFC. It must be able to signal the new defect state to the ingress, i.e. SFF1. Hence the following requirement: REQ#3: SFC OAM MUST support Remote Defect Indication (RDI) notification by egress to the ingress, i.e. source of continuity checking. REQ#4: SFC OAM MUST support connectivity verification. Definition of mis-connectivity defect entry and exit criteria are outside the scope of this document. Once the SFF1 detects the defect objective of OAM switches from failure detection to defect characterization and localization. REQ#5: SFC OAM MUST support fault localization of Loss of Continuity check in the SFC. REQ#6: SFC OAM MUST support tracing an SFP in order to realize the RSP. It is practical, as presented in , that several SFs share the same SFF. In such case SFP1 may be realized over two RSPs, RSP1(SF1--SF3--SF5) and RSP2(SF2--SF4--SF6). REQ#7: SFC OAM MUST have the ability to discover and exercise all available RSPs in the transport network. In process of localizing the SFC failure separating SFC OAM layers is very attractive and efficient approach. To achieve that continuity among SFFs that are part of the same SFP should be verified. Once SFFs reachability along the particular SFP has been confirmed task of defect localization may focus on SF reachability verification. Because reachability of SFFs has already been verified, SFF local to the SF may be used as source. REQ#8: SFC OAM MUST be able to trigger on-demand FM with responses being directed towards initiator of such proxy request.

The multi-layer model OAM that confirms to the above listed requirements enables active OAM protocols that are capable to perform efficient defect localization on an SFC. does not provide definition for identification of an SFC active OAM packet. This document defines that active OAM packet on SFC MUST have OAM bit set and MUST have the value on the Next Protocol field set to OAM (TBA1) according to . It is very unlikely that a single protocol will address all the requirements listed in . Protocols may be identified by destination UDP port number if IP/UDP encapsulation used. But extra IP/UDP headers, especially in case of IPv6, add noticeable overhead. This document defines Active OAM Header to demultiplex active OAM protocols on an SFC.

V - two bits long field indicates the current version of the SFC active OAM header. The current value is 0. Msg Type - six bits long field identifies OAM protocol, e.g. Echo Request/Reply or BFD. Flags - eight bits long field carries bit flags that define optional capability and thus processing of the SFC active OAM control packet, e.g. optional timestamping. Length - two octets long field that is length of the SFC active OAM control packet in octets.

presents a use case of applying the proposed SFC OAM multi-layer model. In this scenario operator needs to discover SFFs and SFs of the same SFC. The Layer 1 includes the SFFs that are part of the SFP. The Layer 2 - the SFs along the RSP. When trying to do SFC OAM, classifier or service nodes select and confirm which SFC OAM layering they plan to do, then encapsulate the layering information in the SFC OAM packets, and send the SFC OAM packets along the service function paths to the destination. When receiving the SFC OAM packets, service nodes analyze the layering information and then decide whether sending these packets to next SFFs directly without being processed by SFs for Layer 1 process or sending to SFs for Layer 2 process.

Echo Request/Reply is well-known active OAM mechanism that is extensively used to detect inconsistencies between states in control plane and data plane, localize defects in the data plane. The format of the Echo request/Echo reply control packet is to support ping and traceroute functionality in SFC in networks resembles the format of MPLS LSP Ping with some exceptions.

The interpretation of the fields is as following: The Version reflects the current version. The version number is to be incremented whenever a change is made that affects the ability of an implementation to correctly parse or process control packet. The Global Flags is a bit vector field The Message Type filed reflects the type of the packet. Value TBA3 identifies echo request and TBA4 - echo reply The Reply Mode defines the type of the return path requested by the sender of the echo request. Return Codes and Subcodes can be used to inform the sender about result of processing its request. The Sender's Handle is filled in by the sender, and returned unchanged by the receiver in the echo reply. The Sequence Number is assigned by the sender and can be (for example) used to detect missed replies. TLVs (Type-Length-Value tuples) have the two octets long Type field, two octets long Length field that is length of the Value field in octets.

SFC echo request control packet MUST use the appropriate encapsulation of the monitored SFP. If Network Service Header (NSH) is used, echo request MUST set O bit, as defined in . SFC NSH MUST be immediately followed by the SFC Active OAM Header defined in . Message Type field in the SFC Active OAM Header MUST be set to SFC Echo Request/Echo Reply value (TBA2) per . Value of the Reply Mode field MAY be set to: Do Not Reply (TBA5) if one-way monitoring is desired. If echo request is used to measure synthetic packet loss, the receiver may report loss measurement results to a remote node. Reply via an IPv4/IPv6 UDP Packet (TBA6) value likely will be the most used. Reply via Application Level Control Channel (TBA7) value if the SFP may have bi-directional paths. Reply via Specified Path (TBA7) value in order to enforce use of the particular return path specified in the included TLV to verify bi-directional continuity and also increase robustness of the monitoring by selecting more stable path.

The Reply Mode field directs whether and how the echo reply message should be sent. The sender of the echo request MAY use TLVs to request that corresponding echo reply be sent using the specified path. Value TBA3 is referred as "Do not reply" mode and suppresses transmission of echo reply packet. 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. Responder to the SFC echo request sends the echo reply over IP network if the Reply mode is Reply via an IPv4/IPv6 UDP Packet. Because SFC NSH does not identify the ingress of the SFP the echo request MUST include this information that to be used as IP destination address for IP/UDP encapsulation of the SFC echo reply. Sender of the SFC echo request MUST include SFC Source TLV .

where SFC OAM Source Id Type is two octets in length and has the value of TBA9 . Length is two octets long field and the values is equal to the length of the Value field. Value field contains IP address of the sender of the SFC OAM control message, IPv4 or IPv6. The UDP destination port for SFC Echo Reply TBA10 will be allocated by IANA .

Overlay Echo Request/Reply operates withing the domain of the overlay network and thus inherits any security considerations that apply to the use of that overlay technology and, consequently, underlay data plane. Also, the security needs for SFC echo request/reply are similar to those of ICMP ping , and MPLS LSP ping . There are at least three approaches of attacking a node in the overlay network using the mechanisms defined in the document. One is a Denial-of-Service attack, by sending SFC ping 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 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. To mitigate potential Denial-of-Service attacks, it is RECOMMENDED that implementations throttle the SFC ping traffic going to the control plane. Reply and spoofing attacks involving faking or replying 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.

IANA is requested to assign new type from the SFC Next Protocol registry as follows: Value Description Reference TBA1 SFC Active OAM This document

IANA is requested to create new 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 as specified in . Remaining code points are allocated according to the table : 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 new type from the SFC Active OAM Message Type registry as follows: Value Description Reference TBA2 SFC Echo Request/Echo Reply This document

IANA is requested to create new SFC Echo Request/Echo Reply Parameters registry.

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 191 in this registry shall be allocated according to the "IETF Review" procedure as specified in and assign values as follows: Value Description Reference 0 Reserved TBA3 SFC Echo Request This document TBA4 SFC Echo Reply This document TBA4+1-191 Unassigned IETF Review 192-251 Unassigned First Come First Served 252-254 Unassigned Private Use 255 Reserved

IANA is requested to create in the SFC Echo Request/Echo Reply Parameters registry the new sub-registry Reply Modes All code points in the range 1 through 191 in this registry shall be allocated according to the "IETF Review" procedure as specified in and assign values as follows: 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 TBA8+1-191 Unassigned IETF Review 192-251 Unassigned First Come First Served 252-254 Unassigned Private Use 255 Reserved

IANA is requested to create SFC OAM TLV Type registry. All code points in the range 1 through 32759 in this registry shall be allocated according to the "IETF Review" procedure as specified in . Code points in the range 32760 through 65279 in this registry shall be allocated according to the "First Come First Served" procedure as specified in . Remaining code points are allocated according to the : Value Description Reference 0 Reserved This document 1- 32759 Unassigned IETF Review 32760 - 65279 Unassigned First Come First Served 65280 - 65519 Experimental This document 65520 - 65534 Private Use This document 65535 Reserved This document This document defines the following new value in SFC OAM TLV Type registry: Value Description Reference TBA9 Source IP Address This document

IANA is requested to allocate UDP port number according to Service Name Port Number Transport Protocol Description Semantics Definition Reference SFC OAM TBA10 UDP SFC OAM This document