Achieving this goal is complicated somewhat by two factors: 1) the need to support the reuse of Template IDs within a Transport Session and 2) the need to support unreliable transmission for Templates when UDP is used as the transport protocol for IPFIX Messages. The Template Management mechanisms defined in this section apply to the export of IPFIX Messages on SCTP, TCP, or UDP. Additional considerations specific to SCTP and UDP transport are given in Sections 8.3 and 8.4, respectively. The Exporting Process assigns and maintains Template IDs per Transport Session and Observation Domain. A newly created Template Record is assigned an unused Template ID by the Exporting Process. The Collecting Process MUST store all received Template Record information for the duration of each Transport Session until reuse or withdrawal as described in Section 8.1, or expiry over UDP as described in Section 8.4, so that it can interpret the corresponding Data Records. The Collecting Process MUST NOT assume that the Template IDs from a given Exporting Process refer to the same Templates as they did in previous Transport Sessions from the same Exporting Process; a Collecting Process MUST NOT use Templates from one Transport Session to decode Data Sets in a subsequent Transport Session. If a specific Information Element is required by a Template but is not present in observed packets, the Exporting Process MAY choose to export Flow Records without this Information Element in a Data Record described by a new Template. If an Information Element is required more than once in a Template, the different occurrences of this Information Element SHOULD follow the logical order of their treatments by the Metering Process. For example, if a selected packet goes through two hash functions, and if the two hash values are sent within a single Template, the first occurrence of the hash value should belong to the first hash function in the Metering Process. For example, when exporting the two source IP addresses of an IPv4-in-IPv4 packet, the first sourceIPv4Address Information Element occurrence should be the IPv4 address of the outer header, while the second occurrence should be the address of the inner header. Collecting Processes MUST properly handle Templates with multiple identical Information Elements. The Exporting Process SHOULD transmit the Template Set and Options Template Set in advance of any Data Sets that use that (Options) Template ID, to help ensure that the Collector has the Template Record before receiving the first Data Record. Data Records that correspond to a Template Record MAY appear in the same and/or
subsequent IPFIX Message(s). However, a Collecting Process MUST NOT assume that the Data Set and the associated Template Set (or Options Template Set) are exported in the same IPFIX Message. Though a Collecting Process normally receives Template Records from the Exporting Process before receiving Data Records, this is not always the case, e.g., in the case of reordering or Collecting Process restart over UDP. In these cases, the Collecting Process MAY buffer Data Records for which it has no Templates, to wait for Template Records describing them; however, note that in the presence of Template withdrawal and redefinition (Section 8.1) this may lead to incorrect interpretation of Data Records. Different Observation Domains within a Transport Session MAY use the same Template ID value to refer to different Templates; Collecting Processes MUST properly handle this case. Options Templates and Templates that are related or interdependent (e.g., by sharing common properties as described in [RFC5473]) SHOULD be sent together in the same IPFIX Message. Section 8.4. A Template Withdrawal consists of a Template Record for the Template ID to be withdrawn, with a Field Count of 0. The format of a Template Withdrawal is shown in Figure T. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Set ID = (2 or 3) | Length = 16 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Template ID N | Field Count = 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Template ID ... | Field Count = 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Template ID M | Field Count = 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure T: Template Withdrawal Format
The Set ID field MUST contain the value 2 for Template Set Withdrawal or the value 3 for Options Template Set Withdrawal. Multiple Template IDs MAY be withdrawn with a single Template Withdrawal; in that case, padding MAY be used. Template Withdrawals MAY appear interleaved with Template Sets, Options Template Sets, and Data Sets within an IPFIX Message. In this case, the Templates and Template Withdrawals shall be interpreted as taking effect in the order in which they appear in the IPFIX Message. An Exporting Process SHOULD NOT send a Template Withdrawal until sufficient time has elapsed to allow receipt and processing of any Data Records described by the withdrawn Templates; see Section 8.2 for details regarding the sequencing of Template management actions. The end of a Transport Session implicitly withdraws all the Templates used within the Transport Session, and Templates must be resent during subsequent Transport Sessions between an Exporting Process and Collecting Process. This applies to SCTP and TCP only; see Sections 8.4 and 10.3.4 for discussions of Transport Session and Template lifetime over UDP. All Templates for a given Observation Domain MAY also be withdrawn using an All Templates Withdrawal, as shown in Figure U. All Options Templates for a given Observation Domain MAY likewise be withdrawn using an All Options Templates Withdrawal, as shown in Figure V. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Set ID = 2 | Length = 8 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Template ID = 2 | Field Count = 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure U: All Templates Withdrawal Set Format 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Set ID = 3 | Length = 8 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Template ID = 3 | Field Count = 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure V: All Options Templates Withdrawal Set Format
Template IDs MAY be reused for new Templates by sending a new Template Record or Options Template Record for a given Template ID after withdrawing the Template. If a Collecting Process receives a Template Withdrawal for a Template or Options Template it does not presently have stored, this indicates a malfunctioning or improperly implemented Exporting Process. The continued receipt and interpretation of Data Records are still possible, but the Collecting Process MUST ignore the Template Withdrawal and SHOULD log the error. If a Collecting Process receives a new Template Record or Options Template Record for an already-allocated Template ID, and that Template or Options Template is identical to the already-received Template or Options Template, it SHOULD log the retransmission; however, this is not an error condition, as it does not affect the interpretation of Data Records. If a Collecting Process receives a new Template Record or Options Template Record for an already-allocated Template ID, and that Template or Options Template is different from the already-received Template or Options Template, this indicates a malfunctioning or improperly implemented Exporting Process. The continued receipt and unambiguous interpretation of Data Records for this Template ID are no longer possible, and the Collecting Process SHOULD log the error. Further Collecting Process actions are out of scope for this specification.
Put another way, a Template describes Data Records contained in IPFIX Messages when the Export Time of such messages is between a specific start and end time, inclusive. The start time is the Export Time of the IPFIX Message containing the Template Record. The end time is one of two times: if the template is withdrawn during the session, then it is the Export Time of the IPFIX Message containing the Template Withdrawal for the template; otherwise, it is the end of the Transport Session. Even if sent in order, IPFIX Messages containing Template management actions could arrive at the Collecting Process out of order, i.e., if sent via UDP or via different SCTP Streams. Given this, Template Withdrawals and subsequent reuse of Template IDs can significantly complicate the problem of determining Template lifetimes at the Collecting Process. A Collecting Process MAY implement a buffer and use Export Time information to disambiguate the order of Template management actions. This buffer, if implemented, SHOULD be configurable to impart a delay on the order of the maximum reordering delay experienced at the Collecting Process. Note, in this case, that the Collecting Process's clock is irrelevant: it is only comparing the Export Times of Messages to each other. Section 8 or Section 8.1, this section takes precedence. Template Sets and Options Template Sets MAY be sent on any SCTP Stream. Data Sets sent on a given SCTP Stream MAY be represented by Template Records exported on any SCTP Stream. Template Sets and Options Template Sets MUST be sent reliably, using SCTP ordered delivery. Template Withdrawals MAY be sent on any SCTP Stream. Template Withdrawals MUST be sent reliably, using SCTP ordered delivery. Template IDs MAY be reused by sending a Template Withdrawal and/or a new Template Record on a different SCTP Stream than the stream on which the original Template was sent. Additional Template Management considerations are provided in [RFC6526], which specifies an extension to explicitly link Templates with SCTP Streams. In exchange for more restrictive rules on the assignment of Template Records to SCTP Streams, this extension allows fast, reliable reuse of Template IDs and estimation of Data Record loss per Template.
Section 8 or Section 8.1, this section takes precedence. Since UDP provides no method for reliable transmission of Templates, Exporting Processes using UDP as the transport protocol MUST periodically retransmit each active Template at regular intervals. The Template retransmission interval MUST be configurable via, for example, the templateRefreshTimeout and optionsTemplateRefreshTimeout parameters as defined in [RFC6728]. Default settings for these values are deployment- and application-specific. Before exporting any Data Records described by a given Template Record or Options Template Record, especially in the case of Template ID reuse as described in Section 8.1, the Exporting Process SHOULD send multiple copies of the Template Record in a separate IPFIX Message, in order to help ensure that the Collecting Process has received it. In order to minimize resource requirements for Templates that are no longer being used by the Exporting Process, the Collecting Process MAY associate a lifetime with each Template received in a Transport Session. Templates not refreshed by the Exporting Process within the lifetime can then be discarded by the Collecting Process. The Template lifetime at the Collecting Process MAY be exposed by a configuration parameter or MAY be derived from observation of the interval of periodic Template retransmissions from the Exporting Process. In this latter case, the Template lifetime SHOULD default to at least 3 times the observed retransmission rate. Template Withdrawals (Section 8.1) MUST NOT be sent by Exporting Processes exporting via UDP and MUST be ignored by Collecting Processes collecting via UDP. Template IDs MAY be reused by Exporting Processes by exporting a new Template for the Template ID after waiting at least 3 times the retransmission delay. Note that Template ID reuse may lead to incorrect interpretation of Data Records if the retransmission and lifetime are not properly configured. When a Collecting Process receives a new Template Record or Options Template Record via UDP for an already-allocated Template ID, and that Template or Options Template is identical to the already- received Template or Options Template, it SHOULD NOT log the retransmission, as this is the normal operation of Template refresh over UDP.
When a Collecting Process receives a new Template Record or Options Template Record for an already-allocated Template ID, and that Template or Options Template is different from the already-received Template or Options Template, the Collecting Process MUST replace the Template or Options Template for that Template ID with the newly received Template or Options Template. This is the normal operation of Template ID reuse over UDP. As Template IDs are unique per UDP session and per Observation Domain, at any given time, the Collecting Process SHOULD maintain the following for all the current Template Records and Options Template Records: <IPFIX Device, Exporter source UDP port, Collector IP address, Collector destination UDP port, Observation Domain ID, Template ID, Template Definition, Last Received>. Sections 9.2 and 9.3, respectively. Template management at Collecting Processes is covered in Section 8. The Collecting Process MUST listen for association requests / connections to start new Transport Sessions from the Exporting Process. The Collecting Process MUST note the Information Element identifier of any Information Element that it does not understand and MAY discard that Information Element from received Data Records. The Collecting Process MUST accept padding in Data Records and Template Records. The padding size is the Set Length minus the size of the Set Header (4 octets for the Set ID and the Set Length), modulo the minimum Record size deduced from the Template Record. The IPFIX protocol has a Sequence Number field in the Export header that increases with the number of IPFIX Data Records in the IPFIX Message. A Collector can detect out-of-sequence, dropped, or duplicate IPFIX Messages by tracking the Sequence Number. A Collector SHOULD provide a logging mechanism for tracking out-of- sequence IPFIX Messages. Such out-of-sequence IPFIX Messages may be due to Exporter resource exhaustion where it cannot transmit messages at their creation rate, an Exporting Process reset, congestion on the network link between the Exporter and Collector, Collector resource exhaustion where it cannot process the IPFIX Messages at their arrival rate, out-of-order packet reception, duplicate packet reception, or an attacker injecting false messages.
Section 10.3 of [RFC5655] Resynchronization should only be attempted if the Collecting Process has reason to believe that the error is transient. On the other hand, the Collecting Process SHOULD stop processing IPFIX Messages from clearly malfunctioning Exporting Processes (e.g., those from which the last few IPFIX Messages have been malformed).
difficult to detect at the Collecting Process, the Collecting Process MAY discard all Transport Session state after no IPFIX Messages are received from a given Exporting Process within a given Transport Session during a configurable idle timeout. The Collecting Process SHOULD accept Data Records without the associated Template Record (or other definitions such as Common Properties) required to decode the Data Record. If the Template Records or other definitions have not been received at the time Data Records are received, the Collecting Process MAY store the Data Records for a short period of time and decode them after the Template Records or other definitions are received, comparing Export Times of IPFIX Messages containing the Template Records with those containing the Data Records as discussed in Section 8.2. Note that this mechanism may lead to incorrectly interpreted records in the presence of Template ID reuse or other identifiers with limited lifetimes. RFC4960] using the Partially Reliable SCTP (PR-SCTP) extension as specified in [RFC3758] MUST be implemented by all compliant implementations. UDP [UDP] MAY also be implemented by compliant implementations. TCP [TCP] MAY also be implemented by compliant implementations.
SCTP should be used in deployments where Exporters and Collectors are communicating over links that are susceptible to congestion. SCTP is capable of providing any required degree of reliability when used with the PR-SCTP extension. TCP may be used in deployments where Exporters and Collectors communicate over links that are susceptible to congestion, but SCTP is preferred, due to its ability to limit back pressure on Exporters and its message-versus-stream orientation. UDP may be used, although it is not a congestion-aware protocol. However, in this case the IPFIX traffic between the Exporter and Collector must be separately contained or provisioned to minimize the risk of congestion-related loss. By default, the Collecting Process listens for connections on SCTP, TCP, and/or UDP port 4739. By default, the Collecting Process listens for secure connections on SCTP, TCP, and/or UDP port 4740 (refer to the Security Considerations section). By default, the Exporting Process attempts to connect to one of these ports. It MUST be possible to configure both the Exporting and Collecting Processes to use different ports than the default. RFC4960] using the PR-SCTP [RFC3758] extension. Section 4.3.
RFC3758]. Using reliable SCTP messages for IPFIX export is not in itself a guarantee that all Data Records will be delivered. If there is congestion on the link from the Exporting Process to the Collecting Process, or if a significant number of retransmissions are required, the send queues on the Exporting Process may fill up; the Exporting Process MAY either suspend, export, or discard the IPFIX Messages. If Data Records are discarded, the IPFIX Sequence Numbers used for export MUST reflect the loss of data.
UDP] in UDP datagrams including IPFIX Messages. Section 8.4 above.
TCP]. Section 4.3.
RFC3917]. The requirements for IPFIX security are as follows: 1. IPFIX must provide a mechanism to ensure the confidentiality of IPFIX data transferred from an Exporting Process to a Collecting Process, in order to prevent disclosure of Flow Records transported via IPFIX. 2. IPFIX must provide a mechanism to ensure the integrity of IPFIX data transferred from an Exporting Process to a Collecting Process, in order to prevent the injection of incorrect data or control information (e.g., Templates), or the duplication of Messages, in an IPFIX Message stream. 3. IPFIX must provide a mechanism to authenticate IPFIX Collecting and Exporting Processes, to prevent the collection of data from an unauthorized Exporting Process or the export of data to an unauthorized Collecting Process. Because IPFIX can be used to collect information for network forensics and billing purposes, attacks designed to confuse, disable, or take information from an IPFIX collection system may be seen as a prime objective during a sophisticated network attack. An attacker in a position to inject false messages into an IPFIX Message stream can affect either the application using IPFIX (by falsifying data) or the IPFIX Collecting Process itself (by modifying or revoking Templates, or changing options); for this reason, IPFIX Message integrity is important. The IPFIX Messages themselves may also contain information of value to an attacker, including information about the configuration of the network as well as end-user traffic and payload data, so care must be taken to confine their visibility to authorized users. When an Information Element containing end-user payload information is exported, it SHOULD be transmitted to the Collecting Process using a means that secures its contents against eavesdropping. Suitable mechanisms include the use of either a direct point-to-point connection assumed to be unavailable to attackers, or the use of an encryption mechanism. It is the responsibility of the Collecting Process to provide a satisfactory degree of security for this collected data, including, if necessary, encryption and/or anonymization of any reported data; see Section 11.8.
RFC5246] and Datagram Transport Layer Security (DTLS) [RFC6347] were designed to provide the confidentiality, integrity, and authentication assurances required by the IPFIX protocol, without the need for pre-shared keys. IPFIX Exporting Processes and Collecting Processes using TCP MUST support TLS version 1.1 and SHOULD support TLS version 1.2 [RFC5246], including the mandatory ciphersuite(s) specified in each version. IPFIX Exporting Processes and Collecting Processes using UDP or SCTP MUST support DTLS version 1.0 and SHOULD support DTLS version 1.2 [RFC6347], including the mandatory ciphersuite(s) specified in each version. Note that DTLS is selected as the security mechanism for SCTP. Though TLS bindings to SCTP are defined in [RFC3436], they require that all communication be over reliable, bidirectional streams, and they also require one TLS connection per stream. This arrangement is not compatible with the rationale behind the choice of SCTP as an IPFIX transport protocol. Note that using DTLS has a man-in-the-middle vulnerability not present in TLS, allowing a message to be removed from the stream without the knowledge of either the sender or receiver. Additionally, when using DTLS over SCTP, an attacker could inject SCTP control information and shut down the SCTP association, causing a loss of IPFIX Messages if those messages are buffered outside of the SCTP association. Techniques such as those described in [RFC6083] could be used to overcome these vulnerabilities. When using DTLS over SCTP, the Exporting Process MUST ensure that each IPFIX Message is sent over the same SCTP Stream that would be used when sending the same IPFIX Message directly over SCTP. Note that DTLS may send its own control messages on stream 0 with full reliability; however, this will not interfere with the processing of stream 0 IPFIX Messages at the Collecting Process, because DTLS consumes its own control messages before passing IPFIX Messages up to the application layer. When using DTLS over SCTP or UDP, the Heartbeat Extension [RFC6520] SHOULD be used, especially on long-lived Transport Sessions, to ensure that the association remains active. Exporting and Collecting Processes MUST NOT request, offer, or use any version of the Secure Socket Layer (SSL), or any version of TLS prior to 1.1, due to known security vulnerabilities in prior versions of TLS; see Appendix E of [RFC5246] for more information.
RFC5246] and [RFC6347], while the IPFIX Collecting Process acts as a TLS or DTLS server. The DTLS client opens a secure connection on SCTP port 4740 of the DTLS server if SCTP is selected as the transport protocol. The TLS client opens a secure connection on TCP port 4740 of the TLS server if TCP is selected as the transport protocol. The DTLS client opens a secure connection on UDP port 4740 of the DTLS server if UDP is selected as the transport protocol. Section 6.4 of [RFC6125]; the inclusion of Common Names (CN-IDs) in certificates identifying IPFIX Exporting Processes or Collecting Processes is NOT RECOMMENDED. To prevent man-in-the-middle attacks from impostor Exporting or Collecting Processes, the acceptance of data from an unauthorized Exporting Process, or the export of data to an unauthorized Collecting Process, mutual authentication MUST be used for both TLS and DTLS. Exporting Processes MUST verify the reference identifiers of the Collecting Processes to which they are exporting IPFIX Messages against those stored in the certificates. Likewise, Collecting Processes MUST verify the reference identifiers of the Exporting Processes from which they are receiving IPFIX Messages against those stored in the certificates. Exporting Processes MUST NOT export to non-verified Collecting Processes, and Collecting Processes MUST NOT accept IPFIX Messages from non-verified Exporting Processes. Exporting Processes and Collecting Processes MUST support the verification of certificates against an explicitly authorized list of peer certificates identified by Common Name and SHOULD support the verification of reference identifiers by matching the DNS-ID or CN-ID with a DNS lookup of the peer. IPFIX Exporting Processes and Collecting Processes MUST use non-NULL ciphersuites for authentication, integrity, and confidentiality.
and partial reliability features, possibly affording some visibility of the attack. The situation is similar with UDP, as some datagrams may continue to be received at the Collecting Process, effectively applying sampling to the IPFIX Message stream and implying that some information about the attack will be available. To minimize IPFIX Message loss under overload conditions, some mechanism for service differentiation could be used to prioritize IPFIX traffic over other traffic on the same link. Alternatively, IPFIX Messages can be transported over a dedicated network. In this case, care must be taken to ensure that the dedicated network can handle the expected peak IPFIX Message traffic. RFC4960] and [RFC6528]); however, UDP offers no such protection. For this reason, IPFIX Message traffic transported via UDP and not secured via DTLS SHOULD be protected via segregation to a dedicated network.
IPFIX Exporting and Collecting Processes SHOULD log any connection attempt that fails due to authentication failure, whether due to being presented an unauthorized or mismatched certificate during TLS or DTLS mutual authentication, or due to a connection attempt from an unauthorized IP address when TLS or DTLS is not in use. IPFIX Exporting and Collecting Processes SHOULD detect and log any SCTP association reset or TCP connection reset. Section 6.1.6.
RFC6615] specifies a MIB module that defines managed objects for monitoring IPFIX Devices, including basic configuration. This MIB can be used to measure the impact of IPFIX export on the monitoring network; it contains tables covering: Transport Session, Cache definition, Observation Point definition, Template and Options Template definition, export features (failover, load-balancing, duplicate), and export statistics per Process, Session, and Template From an operational aspect, an important function of this MIB module is provided by the Transport Session Statistical table, which contains the rate (in bytes per second) at which the Collector receives or the Exporter sends out IPFIX Messages. Of particular interest to operations, the Transport Session Statistical table in Section 5.8.1 of this MIB module exposes the rate of collection or export of IPFIX Messages, which allows the measurement of the bandwidth used by IPFIX export. [RFC6727] describes extensions to the IPFIX-SELECTOR-MIB module specified in [RFC6615] and contains managed objects for providing information on applied packet selection functions and their parameters (filtering and sampling). Since the IPFIX-SELECTOR-MIB [RFC6615] and PSAMP-MIB [RFC6727] modules only contain read-only objects, they cannot be used for configuration of IPFIX Devices. [RFC6728] specifies a configuration data model for the IPFIX and PSAMP protocols, using the Network Configuration Protocol (NETCONF). This data model covers Selection Processes, Caches, Exporting Processes, and Collecting Processes on IPFIX and PSAMP Devices, and is defined using UML (Unified Modeling Language) class diagrams and formally specified using YANG. The configuration data is encoded in Extensible Markup Language (XML). A few mechanisms specified alongside the IPFIX protocol can help monitor and reduce bandwidth used for IPFIX Export: - a bandwidth-saving method for exporting redundant information in IPFIX [RFC5473] - an efficient method for exporting bidirectional flows [RFC5103] - a method for the definition and export of complex data structures [RFC6313]
Alternatively, PSAMP [RFC5474] can be used to export packets sampled by statistical and other methods, which may be applicable to many monitoring areas for which IPFIX is also suited. PSAMP also provides control over the impact on the measured network through its sampling rate. The set of packet selection techniques (Sampling, Filtering, and hashing) standardized by PSAMP is described in [RFC5475]. PSAMP also defines an explicitly configurable export rate limit in Section 8.4 of [RFC5474]. IANA-IPFIX] so that all references that previously pointed to RFC 5101 now point to this document instead. IPFIX Messages use two fields with assigned values. These are the IPFIX Version Number, indicating which version of the IPFIX protocol was used to export an IPFIX Message, and the IPFIX Set ID, indicating the type for each set of information within an IPFIX Message. The Information Elements used by IPFIX, and sub-registries of Information Element values, are managed by IANA [IANA-IPFIX], as are the Private Enterprise Numbers used by enterprise-specific Information Elements [IANA-PEN]. This document makes no changes to these registries. The IPFIX Version Number value of 0x000a (10) is reserved for the IPFIX protocol specified in this document. Set ID values of 0 and 1 are not used, for historical reasons [RFC3954]. The Set ID value of 2 is reserved for the Template Set. The Set ID value of 3 is reserved for the Options Template Set. All other Set ID values from 4 to 255 are reserved for future use. Set ID values above 255 are used for Data Sets. New assignments in either the "IPFIX Version Number" or "IPFIX Set IDs" sub-registries require a Standards Action [RFC5226], i.e., they are to be made via Standards Track RFCs approved by the IESG.