| Internet-Draft | ECN Export in IPFIX | February 2026 |
| Song & Liu | Expires 8 August 2026 | [Page] |
This document defines a set of IP Flow Information Export (IPFIX) Information Elements for monitoring the Low Latency, Low Loss, and Scalable throughput (L4S) service. Specially, these elements enable network operators to monitor the Explicit Congestion Notification (ECN) information of L4S deployment and performance of traffic.¶
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The Low Latency, Low Loss, and Scalable throughput (L4S) service, defined in [RFC9331], introduces a new network service that enables low latency and high throughput for traffic using Scalable congestion controls. To deploy and operate L4S effectively, network operators need visibility into L4S traffic patterns, performance metrics, and interoperability with existing traffic.¶
IP Flow Information Export (IPFIX) [RFC7011] provides a standard protocol for exporting flow information from network devices. This document defines a set of IPFIX Information Elements specifically designed for monitoring L4S ECN traffic.¶
These Information Elements are particularly useful during the experimental phase of L4S deployment as specified in [RFC9331], allowing operators to gather data to examine performance and identify nodes where remediation may be necessary to provide the best performance.¶
This document makes use of the terms defined in [RFC9331], [RFC9330] and [RFC7011].¶
IPFIX: IP Flow Information Export¶
IPFIX Information Elements¶
Observation Point¶
L4S: Low Latency, Low Loss, and Scalable throughput (L4S) service¶
ECN: Explicit Congestion Notification¶
ECT: ECN-capable Transport¶
Not-ECT: Not ECN-capable transport¶
CE: Congestion Experienced¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
For IPv4 packets, the ECN field is located in the Type of Service (TOS) byte of the IP header, specifically in bits 6 to 7. The definition for the IPv4 TOS octet (see [RFC791]) has been superseded by the six-bit DS (Differentiated Services) Field (see [RFC2474], [RFC2780]). Bits 6 and 7 are listed in [RFC2474] as Currently Unused, and are specified in [RFC2780] as approved for experimental use for ECN. The ECN field in IPv4 header is showed as follows.¶
0 1 2 3 4 5 6 7
+-----+-----+-----+-----+-----+-----+-----+-----+
| DS Field, DSCP | ECN Field |
+-----+-----+-----+-----+-----+-----+-----+-----+
ECN Codepoint values:¶
00: Not ECT¶
01: ECT(0)¶
10: ECT(1)¶
11: CE¶
For IPv6 packets, the ECN field is located in bits 6 to 7 of IPv6 Traffic Class. The definition for the IPv6 Traffic Class octet (see [RFC791]) has been superseded by the six-bit DS (Differentiated Services) Field (see [RFC2474], [RFC2780]). Bits 6 and 7 are listed in [RFC2474] as Currently Unused, and are specified in [RFC2780] as approved for experimental use for ECN. The ECN field in IPv6 header is showed as follows.¶
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Version| Traffic Class | Flow Label | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This section defines the Information Elements for L4S ECN. These elements are intended for experimental use in L4S monitoring.¶
ipv4HeaderEcn¶
TBD1¶
This element is used for capturing the complete ECN state of each packet, enabling detailed analysis of congestion notification. The ECN field for IPv4 header is introduced in section 3.1 of this draft. L4S traffic is identified by the ECT(1) as specified in [RFC9331].¶
The Information Element encodes only these 2 bits. Therefore, its value may range from 0 to 3.¶
unsigned8¶
identifier¶
ipv6HeaderEcn¶
TBD2¶
This element is used for capturing the complete ECN state of each packet, enabling detailed analysis of congestion notification. The ECN field format is introduced in section 3.2 of this draft. L4S traffic is identified by the ECT(1) codepoint as specified in [RFC9331].¶
The Information Element encodes only these 2 bits. Therefore, its value may range from 0 to 3.¶
unsigned8¶
identifier¶
mplsHeaderEcn¶
TBD3¶
The EXP field of the MPLS label header is used for carring ECN information in the MPLS domain. As recommended in [RFC5129], explicit congestion notification in MPLS should use codepoints in the EXP field.¶
The Information Element encodes only these 3 bits. Therefore, its value may range from 0 to 7.¶
It is noted that the information extraction of this information element is only used when the MPLS domain has ECN support.¶
unsigned8¶
identifier¶
see [RFC5129] for detailed information for MPLS ECN tunnel negotiation.¶
ipsecSaEcnMode¶
TBD4¶
The information element indicates whether ECN functionality is allowed for an IPsec Security Association (SA) in tunnel encapsulation mode. The IPsec SA Attribute value 10 is defined for ECN tunnel negotiation as defined in section 9.2.1 of [RFC3168]. The negotiation value includes allowed (value set 1) and forbidden (value set 2) attribute. The allowed value enables ECN congestion notifications and the forbidden value disables such notifications.¶
unsigned8¶
identifier¶
See [RFC3168] for detailed information for IPsec tunnel ECN negotiation.¶
l2tpEcnNego¶
TBD5¶
For L2TP tunnels, ECN processing is performed at the L2TP encapsulation layer. [RFC9601] defines an ECN Capability AVP (Type 103) for negotiation between L2TP Control Connection Endpoints. The presence of this AVP indicates support for ECN propagation.¶
unsigned16¶
identifier¶
See [RFC9601] for detailed information for L2TP tunnel ECN negotiation.¶
notEctPacketTotalCount¶
TBD7¶
The total number of packets of this Flow with ECN codepoint set to Not-ECT at the Observation Point since the Metering Process (re-)initialization for this Observation Point.¶
unsigned64¶
totalCounter¶
ect0PacketTotalCount¶
TBD9¶
The total number of packets of this Flow with ECN codepoint set to ECT(0) at the Observation Point since the Metering Process (re-)initialization for this Observation Point.¶
unsigned64¶
totalCounter¶
ect1PacketTotalCount¶
TBD11¶
The total number of packets of this Flow with ECN codepoint set to ECT(1) at the Observation Point since the Metering Process (re-)initialization for this Observation Point.¶
unsigned64¶
totalCounter¶
cePacketTotalCount¶
TBD13¶
The total number of packets of this Flow with ECN codepoint set to CE at the Observation Point since the Metering Process (re-)initialization for this Observation Point.¶
unsigned64¶
totalCounter¶
The IPFIX IEs defined in this draft may have their information extraction positions adjusted based on different ECN monitoring purposes in the network. Among them, the basic ECN field elements are used to reflect the ECN codepoints carried in the IPv4 header, the IPv6 header, or the MPLS header. These fields can be flexibly extracted at any node along the path that has IPFIX export capability. For tunnel ECN negotiation status IEs, the IPFIX data can only be provided by the specific tunnel endpoints that participate in the negotiation. For cumulative statistics IEs, the statistical data may be processed with a higher priority at traffic aggregation or egress nodes.¶
In L4S deployments, CE marking may be either probabilistic or deterministic, as determined by the specific AQM implementation. The IEs on the statiscal count of CE-mark packets is defined to enable operators to perfom quantitative monitoring and management of L4S service performance, typically based on flow data that may be acquired via packet or flow sampling. Implementations should employ sampling methods (see [RFC5475]) that preserve the statistical representativeness of these IEs and reduce bias risk of sampling results.¶
For IPsec tunnels, monitoring ECN requires exporting both outer and inner IP header ECN fields (ipHeaderOuterEcn and ipHeaderInnerEcn), along with ipsecSaEcnMode (see section 4.4 of this draft). Relying solely on the outer IP header ECN field may be insufficient, as it could be set to Not ECT due to tunnel mode restrictions. Similarly, for L2TP tunnels, ECN monitoring should be verified the l2tpEcnNego element (see section 4.5) except the ECN information extraction from tunnel outer header and inner header of packets.¶
For MPLS tunnels, the ECN handling mechanism differs fundamentally from IP based tunnels. ECN information is not carried in a dedicated IP header field but is encoded within the MPLS label stack using the EXP field, as defined in [RFC5129]. Therefore, monitoring ECN over MPLS requires exporting the mplsHeaderEcn element defined in Section 4.3 of this draft. This element captures the congestion indication as conveyed within the MPLS domain, which is independent of the inner IP packet's ECN field.¶
The calculation of derived metrics (e.g., L4S CE marking ratios) from the base counters defined in the section 4 of this draft is an implementation issue for the IPFIX Collector. Operators can utilize the per-flow counts such as ect1PacketTotalCount and cePacketTotalCount for such purposes. The caculation strategy is out of the scope of this draft.¶
The security considerations for IPFIX [RFC7011] apply to this document. The elements for ECN reveal information about endpoint ECN capabilities. Although the information may generally be not sensitive, operators should consider applicable privacy regulations. IPFIX records containing L4S monitoring information SHOULD be transported using secure protocols such as TLS or DTLS and satisfy the mutual authentication between IPFIX Exporting Processes and IPFIX Collecting Processes as specified in [RFC7011].¶
IANA is requested to assign the following Information Elements in the IPFIX Information Elements registry.¶
| Element ID | Name | Reference |
|---|---|---|
| TBD1 | IPv4HeaderEcn | This document |
| TBD2 | IPv6HeaderEcn | This document |
| TBD3 | MPLSHeaderEcn | This document |
| TBD4 | ipsecSaEcnMode | This document |
| TBD5 | l2tpEcnNego | This document |
| TBD6 | notEctPacketDeltaCount | This document |
| TBD7 | notEctPacketTotalCount | This document |
| TBD8 | ect0PacketDeltaCount | This document |
| TBD9 | ect0PacketTotalCount | This document |
| TBD10 | ect1PacketDeltaCount | This document |
| TBD11 | ect1PacketTotalCount | This document |
| TBD12 | cePacketDeltaCount | This document |
| TBD13 | cePacketTotalCount | This document |