Service Function Chaining P. Quinn, Ed. Internet-Draft Cisco Systems, Inc. Intended status: Standards Track U. Elzur, Ed. Expires: November 27, 2016 Intel May 26, 2016 Network Service Header draft-ietf-sfc-nsh-05.txt Abstract This document describes a Network Service Header (NSH) inserted onto encapsulated packets or frames to realize service function paths. NSH also provides a mechanism for metadata exchange along the instantiated service path. NSH is the SFC encapsulation required to support the Service Function Chaining (SFC) Architecture (defined in RFC7665). Quinn & Elzur Expires November 27, 2016 [Page 1] Internet-Draft Network Service Header May 2016 1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on November 27, 2016. Copyright Notice Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Quinn & Elzur Expires November 27, 2016 [Page 2] Internet-Draft Network Service Header May 2016 Table of Contents 1. Requirements Language . . . . . . . . . . . . . . . . . . . . 2 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Definition of Terms . . . . . . . . . . . . . . . . . . . 4 2.2. Problem Space . . . . . . . . . . . . . . . . . . . . . . 5 2.3. NSH-based Service Chaining . . . . . . . . . . . . . . . . 5 3. Network Service Header . . . . . . . . . . . . . . . . . . . . 7 3.1. Network Service Header Format . . . . . . . . . . . . . . 7 3.2. NSH Base Header . . . . . . . . . . . . . . . . . . . . . 7 3.3. Service Path Header . . . . . . . . . . . . . . . . . . . 9 3.4. NSH MD-type 1 . . . . . . . . . . . . . . . . . . . . . . 10 3.5. NSH MD-type 2 . . . . . . . . . . . . . . . . . . . . . . 10 3.5.1. Optional Variable Length Metadata . . . . . . . . . . 11 4. NSH Actions . . . . . . . . . . . . . . . . . . . . . . . . . 13 5. NSH Encapsulation . . . . . . . . . . . . . . . . . . . . . . 15 6. Fragmentation Considerations . . . . . . . . . . . . . . . . . 16 7. Service Path Forwarding with NSH . . . . . . . . . . . . . . . 17 7.1. SFFs and Overlay Selection . . . . . . . . . . . . . . . . 17 7.2. Mapping NSH to Network Transport . . . . . . . . . . . . . 19 7.3. Service Plane Visibility . . . . . . . . . . . . . . . . . 20 7.4. Service Graphs . . . . . . . . . . . . . . . . . . . . . . 20 8. Policy Enforcement with NSH . . . . . . . . . . . . . . . . . 21 8.1. NSH Metadata and Policy Enforcement . . . . . . . . . . . 21 8.2. Updating/Augmenting Metadata . . . . . . . . . . . . . . . 22 8.3. Service Path Identifier and Metadata . . . . . . . . . . . 24 9. NSH Encapsulation Examples . . . . . . . . . . . . . . . . . . 26 9.1. GRE + NSH . . . . . . . . . . . . . . . . . . . . . . . . 26 9.2. VXLAN-gpe + NSH . . . . . . . . . . . . . . . . . . . . . 26 9.3. Ethernet + NSH . . . . . . . . . . . . . . . . . . . . . . 27 10. Security Considerations . . . . . . . . . . . . . . . . . . . 28 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 29 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 32 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33 13.1. NSH EtherType . . . . . . . . . . . . . . . . . . . . . . 33 13.2. Network Service Header (NSH) Parameters . . . . . . . . . 33 13.2.1. NSH Base Header Reserved Bits . . . . . . . . . . . . 33 13.2.2. NSH Version . . . . . . . . . . . . . . . . . . . . . 33 13.2.3. MD Type Registry . . . . . . . . . . . . . . . . . . . 33 13.2.4. MD Class Registry . . . . . . . . . . . . . . . . . . 34 13.2.5. NSH Base Header Next Protocol . . . . . . . . . . . . 34 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 36 14.1. Normative References . . . . . . . . . . . . . . . . . . . 36 14.2. Informative References . . . . . . . . . . . . . . . . . . 36 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 38 Quinn & Elzur Expires November 27, 2016 [Page 3] Internet-Draft Network Service Header May 2016 2. Introduction Service functions are widely deployed and essential in many networks. These service functions provide a range of features such as security, WAN acceleration, and server load balancing. Service functions may be instantiated at different points in the network infrastructure such as the wide area network, data center, campus, and so forth. Prior to development of the SFC architecture [RFC7665] and the protocol specified in this document, current service function deployment models have been relatively static, and bound to topology for insertion and policy selection. Furthermore, they do not adapt well to elastic service environments enabled by virtualization. New data center network and cloud architectures require more flexible service function deployment models. Additionally, the transition to virtual platforms requires an agile service insertion model that supports dynamic and elastic service delivery; the movement of service functions and application workloads in the network and the ability to easily bind service policy to granular information such as per-subscriber state and steer traffic to the requisite service function(s) are necessary. NSH defines a new service plane protocol specifically for the creation of dynamic service chains and is composed of the following elements: 1. Service Function Path identification 2. Transport independent service function chain 3. Per-packet network and service metadata or optional variable type-length-value (TLV) metadata. NSH is designed to be easy to implement across a range of devices, both physical and virtual, including hardware platforms. An NSH-aware control plane is outside the scope of this document. [RFC7665] provides an overview of a service chaining architecture that clearly defines the roles of the various elements and the scope of a service function chaining encapsulation. NSH is the SFC encapsulation referenced in RFC7665 document. 2.1. Definition of Terms Quinn & Elzur Expires November 27, 2016 [Page 4] Internet-Draft Network Service Header May 2016 Classification: Defined in [RFC7665]. Classifier: Defined in [RFC7665]. Metadata: Defined in [RFC7665]. Network Locator: dataplane address, typically IPv4 or IPv6, used to send and receive network traffic. Network Node/Element: Device that forwards packets or frames based on outer header (i.e. transport) information. Network Overlay: Logical network built on top of existing network (the underlay). Packets are encapsulated or tunneled to create the overlay network topology. Service Classifier: Logical entity providing classification function. Since they are logical, classifiers may be co-resident with SFC elements such as SFs or SFFs. Service classifiers perform classification and impose NSH. The initial classifier imposes the initial NSH and sends the NSH packet to the first SFF in the path. Non-initial (i.e. subsequent) classification can occur as needed and can alter, or create a new service path. Service Function (SF): Defined in [RFC7665]. Service Function Chain (SFC): Defined in [RFC7665]. Service Function Forwarder (SFF): Defined in [RFC7665]. Service Function Path (SFP): Defined in [RFC7665]. SFC Proxy: Defined in [RFC7665]. 2.2. Problem Space Network Service Header (NSH) addresses several limitations associated with service function deployments. RFC 7498 [RFC7498] provides a comprehensive review of those issues. 2.3. NSH-based Service Chaining The NSH creates a dedicated service plane, more specifically, NSH enables: 1. Topological Independence: Service forwarding occurs within the service plane, the underlying network topology does not require modification. NSH provides an identifier used to select the Quinn & Elzur Expires November 27, 2016 [Page 5] Internet-Draft Network Service Header May 2016 network overlay for network forwarding. 2. Service Chaining: NSH enables Service Chaining per [RFC7665]. NSH contains path identification information needed to realize a service path. Furthermore, NSH provides the ability to monitor and troubleshoot a service chain, end-to-end via service-specific OAM messages. The NSH fields can be used by administrators (via, for example a traffic analyser) to verify (account, ensure correct chaining, provide reports, etc.) the path specifics of packets being forwarded along a service path. 3. NSH provides a mechanism to carry shared metadata between network devices and service function, and between service functions. The semantics of the shared metadata is communicated via a control plane to participating nodes. Examples of metadata include classification information used for policy enforcement and network context for forwarding post service delivery. 4. Classification and re-classification: sharing the metadata allows service functions to share initial and intermediate classification results with downstream service functions saving re-classification, where enough information was enclosed. 5. NSH offers a common and standards-based header for service chaining to all network and service nodes. 6. Transport Agnostic: NSH is transport independent and is often carried via a network transport protocol, over existing underlays. This transport may form an overlay network and if an existing overlay topology provides the required service path connectivity, that existing overlay may be used. Quinn & Elzur Expires November 27, 2016 [Page 6] Internet-Draft Network Service Header May 2016 3. Network Service Header A Network Service Header (NSH) contains service path information and optionally metadata that are added to a packet or frame and used to create a service plane. The original packets preceded by NSH, are then encapsulated in an outer header for transport. A Service Classifier adds the NSH. The NSH is removed by the last SFF in the service chain or by a SF that consumes the packet. 3.1. Network Service Header Format An NSH is composed of a 4-byte Base Header, a 4-byte Service Path Header and Context Headers, as shown in Figure 1 below. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Base Header | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service Path Header | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Context Headers ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Network Service Header Base header: provides information about the service header and the payload protocol. Service Path Header: provide path identification and location within a service path. Context headers: carry metadata (i.e. context data) along a service path. 3.2. NSH Base Header 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Ver|O|C|R|R|R|R|R|R| Length | MD Type | Next Protocol | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Quinn & Elzur Expires November 27, 2016 [Page 7] Internet-Draft Network Service Header May 2016 Figure 2: NSH Base Header Base Header Field Descriptions: Version: The version field is used to ensure backward compatibility going forward with future NSH updates. It MUST be set to 0x0 by the sender, in this first revision of NSH. Given the widespread implementation of existing hardware that uses the first nibble after an MPLS label stack for ECMP decision processing, this document reserves version 01 and this value MUST NOT be used in future versions of the protocol. O bit: when set to 0x1 indicates that this packet is an Operations, Administration and Maintenance (OAM) message. The receiving SFF and SFs nodes MUST examine the payload and take appropriate action (e.g. return status information). OAM message specifics and handling details are outside the scope of this document. C bit: Indicates that a critical metadata TLV is present. This bit acts as an indication for hardware implementers to decide how to handle the presence of a critical TLV without necessarily needing to parse all TLVs present. For an MD Type of 0x1 (i.e. no variable length metadata is present), the C bit MUST be set to 0x0. All other flag fields are reserved for future use. Reserved bits MUST be set to zero when sent and MUST be ignored upon receipt. Length: total length, in 4-byte words, of NSH including the Base Header, the Service Path Header and the context headers or optional variable length metadata. The Length MUST be of value 0x6 for MD Type equal to 0x1 and MUST be of value 0x2 or greater for MD Type equal to 0x2. The NSH header length MUST be an integer number of 4 bytes. The length field indicates the "end" of NSH and where the original packet/frame begins. MD Type: indicates the format of NSH beyond the mandatory Base Header and the Service Path Header. MD Type defines the format of the metadata being carried. Please see IANA Considerations section below. NSH defines two MD types: 0x1 - which indicates that the format of the header includes fixed length context headers (see Figure 4 below). 0x2 - which does not mandate any headers beyond the Base Header and Service Path Header, but may contain optional variable length context information. Quinn & Elzur Expires November 27, 2016 [Page 8] Internet-Draft Network Service Header May 2016 The format of the base header and the service path header is invariant, and not affected by MD Type. NSH implementations MUST support MD-Type = 0x1, and SHOULD support MD- Type = 0x2. There exists, however, a middle ground, wherein a device will support MD-Type 0x1 (as per the MUST) metadata, yet be deployed in a network with MD-Type 0x2 metadata packets. In that case, the MD-Type 0x1 node, MUST utilize the base header length field to determine the original payload offset if it requires access to the original packet/frame. Next Protocol: indicates the protocol type of the original packet. Please see IANA Considerations section below. This draft defines the following Next Protocol values: 0x1 : IPv4 0x2 : IPv6 0x3 : Ethernet 0x4: NSH 0x5: MPLS 0x6-0xFD: Unassigned 0xFE-0xFF: Experimental 3.3. Service Path Header 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service Path Identifier (SPI) | Service Index | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Service Path Identifier (SPI): 24 bits Service Index (SI): 8 bits Figure 3: NSH Service Path Header Service Path Identifier (SPI): identifies a service path. Participating nodes MUST use this identifier for Service Function Path selection. Service Index (SI): provides location within the SFP. The first classifier (i.e. at the boundary of the NSH domain) in the NSH Service Function Path, SHOULD set the SI to 255, however the control plane MAY configure the initial value of SI as appropriate (i.e. taking into account the length of the service function path). A Quinn & Elzur Expires November 27, 2016 [Page 9] Internet-Draft Network Service Header May 2016 Classifier MUST send the packet to the first SFF in the chain. Service index MUST be decremented by service functions or proxy nodes after performing required services and the new decremented SI value MUST be used in the egress NSH packet. SI SHOULD be used in conjunction with Service Path Identifier for Service Function Path selection. Service Index (SI) is also valuable when troubleshooting/ reporting service paths. In addition to indicating the location within a Service Function Path, SI can be used for service plane loop detection. 3.4. NSH MD-type 1 When the Base Header specifies MD Type = 0x1, four Context Headers, 4-byte each, MUST be added immediately following the Service Path Header, as per Figure 4. Context Headers that carry no metadata MUST be set to zero. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Ver|O|C|R|R|R|R|R|R| Length | MD-type=0x1 | Next Protocol | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service Path Identifer | Service Index | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Mandatory Context Header | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Mandatory Context Header | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Mandatory Context Header | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Mandatory Context Header | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: NSH MD-type=0x1 [dcalloc] and [broadalloc] provide specific examples of how metadata can be allocated. 3.5. NSH MD-type 2 When the base header specifies MD Type= 0x2, zero or more Variable Length Context Headers MAY be added, immediately following the Service Path Header. Therefore, Length = 0x2, indicates that only the Base Header followed by the Service Path Header are present. The optional Variable Length Context Headers MUST be of an integer number Quinn & Elzur Expires November 27, 2016 [Page 10] Internet-Draft Network Service Header May 2016 of 4-bytes. The base header length field MUST be used to determine the offset to locate the original packet or frame for SFC nodes that require access to that information. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Ver|O|C|R|R|R|R|R|R| Length | MD-type=0x2 | Next Protocol | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service Path Identifier | Service Index | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Variable Length Context Headers (opt.) ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 5: NSH MD-type=0x2 3.5.1. Optional Variable Length Metadata The format of the optional variable length context headers, is as described below. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Metadata Class |C| Type |R|R|R| Len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Variable Metadata | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 6: Variable Context Headers Metadata Class (MD Class): describes the scope of the "Type" field. In some cases, the MD Class will identify a specific vendor, in others, the MD Class will identify specific standards body allocated types. Please see IANA Considerations section below. Type: the specific type of information being carried, within the scope of a given MD Class. Value allocation is the responsibility of the MD Class owner. Encoding the criticality of the TLV within the Type field is Quinn & Elzur Expires November 27, 2016 [Page 11] Internet-Draft Network Service Header May 2016 consistent with IPv6 option types: the most significant bit of the Type field indicates whether the TLV is mandatory for the receiver to understand/process. This effectively allocates Type values 0 to 127 for non-critical options and Type values 128 to 255 for critical options. Figure 7 below illustrates the placement of the Critical bit within the Type field. +-+-+-+-+-+-+-+-+ |C| Type | +-+-+-+-+-+-+-+-+ Figure 7: Critical Bit Placement Within the TLV Type Field If an NSH-aware node receives an encapsulated packet containing a TLV with the Critical bit set to 0x1 in the Type field and it does not understand how to process the Type, it MUST drop the packet. Transit devices (i.e. network nodes that do not participate in the service plane) MUST NOT drop packets based on the setting of this bit. Reserved bits: three reserved bit are present for future use. The reserved bits MUST be set to 0x0. Length: Length of the variable metadata, in 4-byte words. A value of 0x0 or higher can be used. A value of 0x0 denotes a TLV header without a Variable Metadata field. Quinn & Elzur Expires November 27, 2016 [Page 12] Internet-Draft Network Service Header May 2016 4. NSH Actions NSH-aware nodes are the only nodes that MAY alter the content of the NSH headers. NSH-aware nodes include: service classifiers, SFF, SF and SFC proxies. These nodes have several possible header related actions: 1. Insert or remove NSH: These actions can occur at the start and end respectively of a service path. Packets are classified, and if determined to require servicing, NSH will be imposed. A service classifier MUST insert NSH at the start of an SFP. An imposed NSH MUST contain valid Base Header and Service Path Header. At the end of a service function path, a SFF, MUST be the last node operating on the service header and MUST remove it. Multiple logical classifiers may exist within a given service path. Non-initial classifiers may re-classify data and that re- classification MAY result in a new Service Function Path. When the logical classifier performs re-classification that results in a change of service path, it MUST remove the existing NSH and MUST impose a new NSH with the Base Header and Service Path Header reflecting the new service path information and set the initial SI. Metadata MAY be preserved in the new NSH. 2. Select service path: The Service Path Header provides service chain information and is used by SFFs to determine correct service path selection. SFFs MUST use the Service Path Header for selecting the next SF or SFF in the service path. 3. Update a Service Path Header: NSH-aware service functions (SF) MUST decrement the service index. If an SFF receives a packet with SI equal to 0x0, that packet MUST be dropped by the SFF. Classifier(s) MAY update Context Headers if new/updated context is available. If an SFC proxy is in use (acting on behalf of a non-NSH-aware service function for NSH actions), then the proxy MUST update Service Index and MAY update contexts. When an SFC proxy receives an NSH-encapsulated packet, it MUST remove the NSH headers before forwarding it to an NSH unaware SF. When the SFC Proxy receives a packet back from an NSH unaware SF, it MUST re- encapsulates it with the correct NSH, and MUST decrement the Service Index. Quinn & Elzur Expires November 27, 2016 [Page 13] Internet-Draft Network Service Header May 2016 4. Service policy selection: Service Function instances derive policy (i.e. service actions such as permit or deny) selection and enforcement from the service header. Metadata shared in the service header can provide a range of service-relevant information such as traffic classification. Service functions SHOULD use NSH to select local service policy. Figure 8 maps each of the four actions above to the components in the SFC architecture that can perform it. +---------------+------------------+-------+----------------+---------+ | | Insert |Select | Update |Service | | | or remove NSH |Service| NSH |policy | | | |Function| |selection| | Component +--------+--------+Path +----------------+ | | | | | | Dec. |Update | | | | Insert | Remove | |Service |Context| | | | | | | Index |Header | | +----------------+--------+--------+-------+--------+-------+---------+ | | + | + | | | + | | |Classifier | | | | | | | +--------------- +--------+--------+-------+--------+-------+---------+ |Service Function| | + | + | | | | |Forwarder(SFF) | | | | | | | +--------------- +--------+--------+-------+--------+-------+---------+ |Service | | | | + | + | + | |Function (SF) | | | | | | | +--------------- +--------+--------+-------+--------+-------+---------+ |SFC Proxy | + | + | | + | | | +----------------+--------+--------+-------+--------+-------+---------+ Figure 8: NSH Action and Role Mapping Quinn & Elzur Expires November 27, 2016 [Page 14] Internet-Draft Network Service Header May 2016 5. NSH Encapsulation Once NSH is added to a packet, an outer encapsulation is used to forward the original packet and the associated metadata to the start of a service chain. The encapsulation serves two purposes: 1. Creates a topologically independent services plane. Packets are forwarded to the required services without changing the underlying network topology 2. Transit network nodes simply forward the encapsulated packets as is. The service header is independent of the encapsulation used and is encapsulated in existing transports. The presence of NSH is indicated via protocol type or other indicator in the outer encapsulation. See Section 9 for NSH encapsulation examples. Quinn & Elzur Expires November 27, 2016 [Page 15] Internet-Draft Network Service Header May 2016 6. Fragmentation Considerations NSH and the associated transport header are "added" to the encapsulated packet/frame. This additional information increases the size of the packet. In order the ensure proper forwarding of NSH packets, several options for handling fragmentation and re-assembly exist: 1. Jumbo Frames, when supported, enable the transport of NSH and associated transport packets without requiring fragmentation. 2. and [RFC1191][RFC1981] describe a technique for dynamically discovering the maximum transmission unit (MTU) of an arbitrary internet path" and can be utilized to ensure the required packet size is used. 3. Use the fragmentation provided by the network transport/overlay. One example can be found in [RFC6830], section 5.4. Quinn & Elzur Expires November 27, 2016 [Page 16] Internet-Draft Network Service Header May 2016 7. Service Path Forwarding with NSH 7.1. SFFs and Overlay Selection As described above, NSH contains a Service Path Identifier (SPI) and a Service Index (SI). The SPI is, as per its name, an identifier. The SPI alone cannot be used to forward packets along a service path. Rather the SPI provide a level of indirection between the service path/topology and the network transport. Furthermore, there is no requirement, or expectation of an SPI being bound to a pre-determined or static network path. The Service Index provides an indication of location within a service path. The combination of SPI and SI provides the identification of a logical SF and its order within the service plane, and is used to select the appropriate network locator(s) for overlay forwarding. The logical SF may be a single SF, or a set of eligible SFs that are equivalent. In the latter case, the SFF provides load distribution amongst the collection of SFs as needed. SI can also serve as a mechanism for loop detection within a service path since each SF in the path decrements the index; an Service Index of 0 indicates that a loop occurred and the packet must be discarded. This indirection -- path ID to overlay -- creates a true service plane. That is the SFF/SF topology is constructed without impacting the network topology but more importantly service plane only participants (i.e. most SFs) need not be part of the network overlay topology and its associated infrastructure (e.g. control plane, routing tables, etc.). As mentioned above, an existing overlay topology may be used provided it offers the requisite connectivity. The mapping of SPI to transport occurs on an SFF (as discussed above, the first SFF in the path gets a NSH encapsulated packet from the Classifier). The SFF consults the SPI/ID values to determine the appropriate overlay transport protocol (several may be used within a given network) and next hop for the requisite SF. Figure 9 below depicts an example of a single next-hop SPI/SI to network overlay network locator mapping. Quinn & Elzur Expires November 27, 2016 [Page 17] Internet-Draft Network Service Header May 2016 +-------------------------------------------------------+ | SPI | SI | NH | Transport | +-------------------------------------------------------+ | 10 | 255 | 192.0.2.1 | VXLAN-gpe | | 10 | 254 | 198.51.100.10 | GRE | | 10 | 251 | 198.51.100.15 | GRE | | 40 | 251 | 198.51.100.15 | GRE | | 50 | 200 | 01:23:45:67:89:ab | Ethernet | | 15 | 212 | Null (end of path) | None | +-------------------------------------------------------+ Figure 9: SFF NSH Mapping Example Additionally, further indirection is possible: the resolution of the required SF network locator may be a localized resolution on an SFF, rather than a service function chain control plane responsibility, as per figures 10 and 11 below. Please note: VXLAN-gpe and GRE in the above table refer to [VXLAN-gpe] and [RFC2784], respectively. +-------------------+ | SPI | SI | NH | +-------------------+ | 10 | 3 | SF2 | | 245 | 12 | SF34 | | 40 | 9 | SF9 | +-------------------+ Figure 10: NSH to SF Mapping Example +----------------------------------------+ | SF | NH | Transport | +----------------------------------------| | SF2 | 192.0.2.2 | VXLAN-gpe | | SF34| 198.51.100.34 | UDP | | SF9 | 2001:db8::1 | GRE | +--------------------------+------------- = Quinn & Elzur Expires November 27, 2016 [Page 18] Internet-Draft Network Service Header May 2016 Figure 11: SF Locator Mapping Example Since the SPI is a representation of the service path, the lookup may return more than one possible next-hop within a service path for a given SF, essentially a series of weighted (equally or otherwise) paths to be used (for load distribution, redundancy or policy), see Figure 12. The metric depicted in Figure 12 is an example to help illustrated weighing SFs. In a real network, the metric will range from a simple preference (similar to routing next- hop), to a true dynamic composite metric based on some service function-centric state (including load, sessions state, capacity, etc.) +----------------------------------+ | SPI | SI | NH | Metric | +----------------------------------+ | 10 | 3 | 203.0.113.1 | 1 | | | | 203.0.113.2 | 1 | | | | | | | 20 | 12 | 192.0.2.1 | 1 | | | | 203.0.113.4 | 1 | | | | | | | 30 | 7 | 192.0.2.10 | 10 | | | | 198.51.100.1| 5 | +----------------------------------+ (encapsulation type omitted for formatting) Figure 12: NSH Weighted Service Path 7.2. Mapping NSH to Network Transport As described above, the mapping of SPI to network topology may result in a single path, or it might result in a more complex topology. Furthermore, the SPI to overlay mapping occurs at each SFF independently. Any combination of topology selection is possible. Please note, there is no requirement to create a new overlay topology if a suitable one already existing. NSH packets can use any (new or existing) overlay provided the requisite connectivity requirements are satisfied. Examples of mapping for a topology: 1. Next SF is located at SFFb with locator 192.0.2.1 SFFa mapping: SPI=10 --> VXLAN-gpe, dst-ip: 192.0.2.1 Quinn & Elzur Expires November 27, 2016 [Page 19] Internet-Draft Network Service Header May 2016 2. Next SF is located at SFFc with multiple network locators for load distribution purposes: SFFb mapping: SPI=10 --> VXLAN-gpe, dst_ip:203.0.113.1, 203.0.113.2, 203.0.113.3, equal cost 3. Next SF is located at SFFd with two paths from SFFc, one for redundancy: SFFc mapping: SPI=10 --> VXLAN-gpe, dst_ip:192.0.2.10 cost=10, 203.0.113.10, cost=20 In the above example, each SFF makes an independent decision about the network overlay path and policy for that path. In other words, there is no a priori mandate about how to forward packets in the network (only the order of services that must be traversed). The network operator retains the ability to engineer the network paths as required. For example, the overlay path between SFFs may utilize traffic engineering, QoS marking, or ECMP, without requiring complex configuration and network protocol support to be extended to the service path explicitly. In other words, the network operates as expected, and evolves as required, as does the service plane. 7.3. Service Plane Visibility The SPI and SI serve an important function for visibility into the service topology. An operator can determine what service path a packet is "on", and its location within that path simply by viewing the NSH information (packet capture, IPFIX, etc.). The information can be used for service scheduling and placement decisions, troubleshooting and compliance verification. 7.4. Service Graphs While a given realized service function path is a specific sequence of service functions, the service as seen by a user can actually be a collection of service function paths, with the interconnection provided by classifiers (in-service path, non-initial reclassification). These internal reclassifiers examine the packet at relevant points in the network, and rewrite the SPI and SI to reflect the results of the reclassification. (These classifiers may also of course modify the metadata associated with the packet.) RFC7665, section 2.1 describes Service Graphs in detail. Quinn & Elzur Expires November 27, 2016 [Page 20] Internet-Draft Network Service Header May 2016 8. Policy Enforcement with NSH 8.1. NSH Metadata and Policy Enforcement As described in Section 3, NSH provides the ability to carry metadata along a service path. This metadata may be derived from several sources, common examples include: Network nodes/devices: Information provided by network nodes can indicate network-centric information (such as VRF or tenant) that may be used by service functions, or conveyed to another network node post service path egress. External (to the network) systems: External systems, such as orchestration systems, often contain information that is valuable for service function policy decisions. In most cases, this information cannot be deduced by network nodes. For example, a cloud orchestration platform placing workloads "knows" what application is being instantiated and can communicate this information to all NSH nodes via metadata carried in the context header(s). Service Functions: A classifier co-resident with Service Functions often perform very detailed and valuable classification. In some cases they may terminate, and be able to inspect encrypted traffic. Regardless of the source, metadata reflects the "result" of classification. The granularity of classification may vary. For example, a network switch, acting as a classifier, might only be able to classify based on a 5-tuple, whereas, a service function may be able to inspect application information. Regardless of granularity, the classification information can be represented in NSH. Once the data is added to NSH, it is carried along the service path, NSH-aware SFs receive the metadata, and can use that metadata for local decisions and policy enforcement. The following two examples highlight the relationship between metadata and policy: Quinn & Elzur Expires November 27, 2016 [Page 21] Internet-Draft Network Service Header May 2016 +-------+ +-------+ +-------+ | SFF )------->( SFF |------->| SFF | +---^---+ +---|---+ +---|---+ ,-|-. ,-|-. ,-|-. / \ / \ / \ ( Class ) SF1 ) ( SF2 ) \ ify / \ / \ / `---' `---' `---' 5-tuple: Permit Inspect Tenant A Tenant A AppY AppY Figure 13: Metadata and Policy +-----+ +-----+ +-----+ | SFF |---------> | SFF |----------> | SFF | +--+--+ +--+--+ +--+--+ ^ | | ,-+-. ,-+-. ,-+-. / \ / \ / \ ( Class ) ( SF1 ) ( SF2 ) \ ify / \ / \ / `-+-' `---' `---' | Permit Deny AppZ +---+---+ employees | | +-------+ external system: Employee AppZ Figure 14: External Metadata and Policy In both of the examples above, the service functions perform policy decisions based on the result of the initial classification: the SFs did not need to perform re-classification, rather they rely on a antecedent classification for local policy enforcement. 8.2. Updating/Augmenting Metadata Post-initial metadata imposition (typically performed during initial service path determination), metadata may be augmented or updated: Quinn & Elzur Expires November 27, 2016 [Page 22] Internet-Draft Network Service Header May 2016 1. Metadata Augmentation: Information may be added to NSH's existing metadata, as depicted in Figure 17. For example, if the initial classification returns the tenant information, a secondary classification (perhaps co-resident with DPI or SLB) may augment the tenant classification with application information, and impose that new information in the NSH metadata. The tenant classification is still valid and present, but additional information has been added to it. 2. Metadata Update: Subsequent classifiers may update the initial classification if it is determined to be incorrect or not descriptive enough. For example, the initial classifier adds metadata that describes the traffic as "internet" but a security service function determines that the traffic is really "attack". Figure 18 illustrates an example of updating metadata. +-----+ +-----+ +-----+ | SFF |---------> | SFF |----------> | SFF | +--+--+ +--+--+ +--+--+ ^ | | ,---. ,---. ,---. / \ / \ / \ ( Class ) ( SF1 ) ( SF2 ) \ / \ / \ / `-+-' `---' `---' | Inspect Deny +---+---+ employees employee+ | | Class=AppZ appZ +-------+ external system: Employee Figure 15: Metadata Augmentation Quinn & Elzur Expires November 27, 2016 [Page 23] Internet-Draft Network Service Header May 2016 +-----+ +-----+ +-----+ | SFF |---------> | SFF |----------> | SFF | +--+--+ +--+--+ +--+--+ ^ | | ,---. ,---. ,---. / \ / \ / \ ( Class ) ( SF1 ) ( SF2 ) \ / \ / \ / `---' `---' `---' 5-tuple: Inspect Deny Tenant A Tenant A attack --> attack Figure 16: Metadata Update 8.3. Service Path Identifier and Metadata Metadata information may influence the service path selection since the Service Path Identifier can represent the result of classification. A given SPI can represent all or some of the metadata, and be updated based on metadata classification results. This relationship provides the ability to create a dynamic service plane based on complex classification without requiring each node to be capable of such classification, or requiring a coupling to the network topology. This yields service graph functionality as described in Section 7.4. Figure 19 illustrates an example of this behavior. Quinn & Elzur Expires November 27, 2016 [Page 24] Internet-Draft Network Service Header May 2016 +-----+ +-----+ +-----+ | SFF |---------> | SFF |------+---> | SFF | +--+--+ +--+--+ | +--+--+ | | | | ,---. ,---. | ,---. / \ / \ | / \ ( SCL ) ( SF1 ) | ( SF2 ) \ / \ / | \ / `---' `---' +-----+ `---' 5-tuple: Inspect | SFF | Original Tenant A Tenant A +--+--+ next SF --> DoS | V ,-+-. / \ ( SF10 ) \ / `---' DoS "Scrubber" Figure 17: Path ID and Metadata Specific algorithms for mapping metadata to an SPI are outside the scope of this document. Quinn & Elzur Expires November 27, 2016 [Page 25] Internet-Draft Network Service Header May 2016 9. NSH Encapsulation Examples 9.1. GRE + NSH IPv4 Packet: +----------+--------------------+--------------------+ |L2 header | L3 header, proto=47|GRE header,PT=0x894F| +----------+--------------------+--------------------+ --------------+----------------+ NSH, NP=0x1 |original packet | --------------+----------------+ L2 Frame: +----------+--------------------+--------------------+ |L2 header | L3 header, proto=47|GRE header,PT=0x894F| +----------+--------------------+--------------------+ ---------------+---------------+ NSH, NP=0x3 |original frame | ---------------+---------------+ Figure 18: GRE + NSH 9.2. VXLAN-gpe + NSH IPv4 Packet: +----------+------------------------+---------------------+ |L2 header | IP + UDP dst port=4790 |VXLAN-gpe NP=0x4(NSH)| +----------+------------------------+---------------------+ --------------+----------------+ NSH, NP=0x1 |original packet | --------------+----------------+ L2 Frame: +----------+------------------------+---------------------+ |L2 header | IP + UDP dst port=4790 |VXLAN-gpe NP=0x4(NSH)| +----------+------------------------+---------------------+ ---------------+---------------+ NSH,NP=0x3 |original frame | ---------------+---------------+ Figure 19: VXLAN-gpe + NSH Quinn & Elzur Expires November 27, 2016 [Page 26] Internet-Draft Network Service Header May 2016 9.3. Ethernet + NSH IPv4 Packet: +-------------------------------+---------------+--------------------+ |Outer Ethernet, ET=0x894F | NSH, NP = 0x1 | original IP Packet | +-------------------------------+---------------+--------------------+ L2 Frame: +-------------------------------+---------------+----------------+ |Outer Ethernet, ET=0x894F | NSH, NP = 0x3 | original frame | +-------------------------------+---------------+----------------+ Figure 20: Ethernet + NSH Quinn & Elzur Expires November 27, 2016 [Page 27] Internet-Draft Network Service Header May 2016 10. Security Considerations As with many other protocols, NSH data can be spoofed or otherwise modified. In many deployments, NSH will be used in a controlled environment, with trusted devices (e.g. a data center) thus mitigating the risk of unauthorized header manipulation. NSH is always encapsulated in a transport protocol and therefore, when required, existing security protocols that provide authenticity (e.g. RFC 2119 [RFC6071]) can be used. Similarly if confidentiality is required, existing encryption protocols can be used in conjunction with encapsulated NSH. Further security considerations are discussed in [nsh-sec]. Quinn & Elzur Expires November 27, 2016 [Page 28] Internet-Draft Network Service Header May 2016 11. Contributors This WG document originated as draft-quinn-sfc-nsh and had the following co-authors and contributors. The editors of this document would like to thank and recognize them and their contributions. These co-authors and contributors provided invaluable concepts and content for this document's creation. Surendra Kumar Cisco Systems smkumar@cisco.com Michael Smith Cisco Systems michsmit@cisco.com Jim Guichard Cisco Systems jguichar@cisco.com Rex Fernando Cisco Systems Email: rex@cisco.com Navindra Yadav Cisco Systems Email: nyadav@cisco.com Wim Henderickx Alcatel-Lucent wim.henderickx@alcatel-lucent.com Andrew Dolganow Alcaltel-Lucent Email: andrew.dolganow@alcatel-lucent.com Praveen Muley Alcaltel-Lucent Email: praveen.muley@alcatel-lucent.com Tom Nadeau Brocade tnadeau@lucidvision.com Puneet Agarwal puneet@acm.org Rajeev Manur Quinn & Elzur Expires November 27, 2016 [Page 29] Internet-Draft Network Service Header May 2016 Broadcom rmanur@broadcom.com Abhishek Chauhan Citrix Abhishek.Chauhan@citrix.com Joel Halpern Ericsson joel.halpern@ericsson.com Sumandra Majee F5 S.Majee@f5.com David Melman Marvell davidme@marvell.com Pankaj Garg Microsoft pankajg@microsoft.com Brad McConnell Rackspace bmcconne@rackspace.com Chris Wright Red Hat Inc. chrisw@redhat.com Kevin Glavin Riverbed kevin.glavin@riverbed.com Hong (Cathy) Zhang Huawei US R&D cathy.h.zhang@huawei.com Louis Fourie Huawei US R&D louis.fourie@huawei.com Ron Parker Affirmed Networks ron_parker@affirmednetworks.com Myo Zarny Quinn & Elzur Expires November 27, 2016 [Page 30] Internet-Draft Network Service Header May 2016 Goldman Sachs myo.zarny@gs.com Quinn & Elzur Expires November 27, 2016 [Page 31] Internet-Draft Network Service Header May 2016 12. Acknowledgments The authors would like to thank Nagaraj Bagepalli, Abhijit Patra, Peter Bosch, Darrel Lewis, Pritesh Kothari, Tal Mizrahi and Ken Gray for their detailed review, comments and contributions. A special thank you goes to David Ward and Tom Edsall for their guidance and feedback. Additionally the authors would like to thank Carlos Pignataro and Larry Kreeger for their invaluable ideas and contributions which are reflected throughout this document. Loa Andersson provided a thorough review and valuable comments, we thank him for that. Lastly, Reinaldo Penno deserves a particular thank you for his architecture and implementation work that helped guide the protocol concepts and design. Quinn & Elzur Expires November 27, 2016 [Page 32] Internet-Draft Network Service Header May 2016 13. IANA Considerations 13.1. NSH EtherType An IEEE EtherType, 0x894F, has been allocated for NSH. 13.2. Network Service Header (NSH) Parameters IANA is requested to create a new "Network Service Header (NSH) Parameters" registry. The following sub-sections request new registries within the "Network Service Header (NSH) Parameters " registry. 13.2.1. NSH Base Header Reserved Bits There are ten bits at the beginning of the NSH Base Header. New bits are assigned via Standards Action [RFC5226]. Bits 0-1 - Version Bit 2 - OAM (O bit) Bit 3 - Critical TLV (C bit) Bits 4-9 - Reserved 13.2.2. NSH Version IANA is requested to setup a registry of "NSH Version". New values are assigned via Standards Action [RFC5226]. Version 00: This protocol version. This document. Version 01: Reserved. This document. Version 10: Unassigned. Version 11: Unassigned. 13.2.3. MD Type Registry IANA is requested to set up a registry of "MD Types". These are 8-bit values. MD Type values 0, 1, 2, 254, and 255 are specified in this document. Registry entries are assigned by using the "IETF Review" policy defined in RFC 5226 [RFC5226]. Quinn & Elzur Expires November 27, 2016 [Page 33] Internet-Draft Network Service Header May 2016 +---------+--------------+---------------+ | MD Type | Description | Reference | +---------+--------------+---------------+ | 0 | Reserved | This document | | | | | | 1 | NSH | This document | | | | | | 2 | NSH | This document | | | | | | 3..253 | Unassigned | | | | | | | 254 | Experiment 1 | This document | | | | | | 255 | Experiment 2 | This document | +---------+--------------+---------------+ Table 1 13.2.4. MD Class Registry IANA is requested to set up a registry of "MD Class". These are 16- bit values. Registry entries are assigned by using the "IETF Review" policy defined in RFC 5226 [RFC5226]. TLV Classes defined by this document are listed below. New values are assigned via Standards Action [RFC5226]. 0x0000 to 0x01ff: IETF Consensus 0x0200 to 0x7fff: Expert Review 0xfff6 to 0xfffe: Experimental 0xffff: Reserved 13.2.5. NSH Base Header Next Protocol IANA is requested to set up a registry of "Next Protocol". These are 8-bit values. Next Protocol values 0, 1, 2, 3, 4 and 5 are defined in this draft. New values are assigned via Standards Action [RFC5226]. Quinn & Elzur Expires November 27, 2016 [Page 34] Internet-Draft Network Service Header May 2016 +---------------+--------------+---------------+ | Next Protocol | Description | Reference | +---------------+--------------+---------------+ | 0 | Reserved | This document | | | | | | 1 | IPv4 | This document | | | | | | 2 | IPv6 | This document | | | | | | 3 | Ethernet | This document | | | | | | 4 | NSH | This document | | | | | | 5 | MPLS | This document | | | | | | 6..253 | Unassigned | | | | | | | 254 | Experiment 1 | This document | | | | | | 255 | Experiment 2 | This document | +---------------+--------------+---------------+ Table 2 Quinn & Elzur Expires November 27, 2016 [Page 35] Internet-Draft Network Service Header May 2016 14. References 14.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ RFC2119, March 1997, . [RFC7498] Quinn, P., Ed. and T. Nadeau, Ed., "Problem Statement for Service Function Chaining", RFC 7498, DOI 10.17487/ RFC7498, April 2015, . [RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function Chaining (SFC) Architecture", RFC 7665, DOI 10.17487/ RFC7665, October 2015, . 14.2. Informative References [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, DOI 10.17487/RFC1191, November 1990, . [RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery for IP version 6", RFC 1981, DOI 10.17487/RFC1981, August 1996, . [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, DOI 10.17487/RFC2784, March 2000, . [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, DOI 10.17487/RFC5226, May 2008, . [RFC6071] Frankel, S. and S. Krishnan, "IP Security (IPsec) and Internet Key Exchange (IKE) Document Roadmap", RFC 6071, DOI 10.17487/RFC6071, February 2011, . [RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The Locator/ID Separation Protocol (LISP)", RFC 6830, DOI 10.17487/RFC6830, January 2013, . Quinn & Elzur Expires November 27, 2016 [Page 36] Internet-Draft Network Service Header May 2016 [VXLAN-gpe] Quinn, P., Manur, R., Agarwal, P., Kreeger, L., Lewis, D., Maino, F., Smith, M., Yong, L., Xu, X., Elzur, U., Garg, P., and D. Melman, "Generic Protocol Extension for VXLAN", . [broadalloc] Napper, J., Kumar, S., Muley, P., and W. Hendericks, "NSH Context Header Allocation -- Mobility", 2016, . [dcalloc] Guichard, J., Smith, M., and et al., "Network Service Header (NSH) Context Header Allocation (Data Center)", 2016, . [nsh-sec] Reddy, T., Migault, D., Pignataro, C., Quinn, P., and C. Inacio, "NSH Security and Privacy requirements", 2016, . Quinn & Elzur Expires November 27, 2016 [Page 37] Internet-Draft Network Service Header May 2016 Authors' Addresses Paul Quinn (editor) Cisco Systems, Inc. Email: paulq@cisco.com Uri Elzur (editor) Intel Email: uri.elzur@intel.com Quinn & Elzur Expires November 27, 2016 [Page 38]