Deterministic Networking (DetNet) Data Plane: MPLS over UDP/IP
Extracted elements (19)
Four requirements must be satisfied to carry DetNet MPLS flows over an IP network: flow identification, DetNet sequence number carriage, OAM/data distinction, and queuing/forwarding indication. The MPLS encapsulation (RFC 8964) fully satisfies all four; the DetNet IP data plane (RFC 8939) only partially satisfies them (no sequence number).
In the presence of network (and port) address translation devices/functions, it is the responsibility of the Controller Plane to determine the appropriate information to ensure proper flow mapping at the sender/receiver.
RFC 7510 prohibits MPLS-in-UDP over the general Internet or non-cooperating network operators for non-congestion-controlled traffic. This constraint is compatible with DetNet because DetNet is constrained to operate within a single administrative control or a closed group of administrative control.
The MPLS DetNet encapsulation from RFC 8964 is mapped to the DetNet IP data plane by replacing F-Labels with UDP and IP headers, modeled on MPLS-over-UDP per RFC 7510. There may be zero or more F-Labels between the S-Label and the UDP header, giving flexibility in the degree of replacement.
UDP checksum use must be evaluated on a case-by-case basis per network scenario based on the exception criteria in RFC 7510, particularly when IPv6 is used. This reflects a deliberate trade-off between overhead and integrity guarantees in controlled DetNet environments.
The UDP/IP encapsulation of DetNet MPLS works equally well with IPv4, IPv6, and IPv6-based Segment Routing (RFC 8754), providing broad compatibility across IP network types.
After encapsulation, the packet MUST be handled as a DetNet IP packet per RFC 8939, including QoS-related traffic treatment.
After flow identification on receive, normal receive processing as defined in RFC 8964, including PEF (Packet Elimination Function) and POF (Packet Ordering Function), can then take place.
The minimum configuration information (label mappings, IP source/destination, DSCP, UDP source/destination ports, UDP checksum use) MUST be provisioned per DetNet flow via configuration, e.g., via the controller or management plane.
The UDP and IP headers for each outgoing packet MUST be formatted according to the configuration information and as defined in RFC 7510.
The UDP Source Port value MUST be set to uniquely identify the DetNet flow. This ensures flow-level identification within the UDP/IP encapsulation layer.
To support outgoing DetNet MPLS over UDP encapsulation, an implementation MUST support the provisioning of UDP and IP header information in addition to or in place of F-Labels. When PRF is performed at the MPLS service sub-layer, each member flow requires its own provisioned UDP and IP header information.
To support receive processing, an implementation MUST also support provisioning of received UDP and IP header information. The provisioned information MUST be used to identify incoming app flows based on the combination of S-Label and incoming encapsulation header information.
The DetNet Control Word (d-CW) is used for sequencing and identifying duplicate packets of a DetNet flow at the DetNet service sub-layer. It is defined in RFC 8964 and is not modified by this document.
The F-Label is a DetNet 'forwarding' label that identifies the LSP used to forward a DetNet flow across an MPLS PSN, e.g., a hop-by-hop label used between label-switching routers. This document allows F-Labels to be partly or entirely replaced by UDP and IP headers.
The minimum configuration set for DetNet MPLS over UDP/IP includes: A-Labels, S-Labels, and F-Labels mapped to UDP/IP flows; IPv4 or IPv6 source and destination addresses; DSCP field in IPv4 ToS or IPv6 Traffic Class; UDP Source Port; UDP Destination Port; and whether to use the UDP checksum.
The S-Label is a DetNet 'service' label used between DetNet nodes that implement the DetNet service sub-layer functions; it also identifies a DetNet flow at the service sub-layer. A special case, the A-Label, has properties known only at aggregation and deaggregation endpoints.
This document reuses mechanisms from RFC 7510 (MPLS-over-UDP), RFC 8655 (DetNet architecture), RFC 8964 (DetNet MPLS), and RFC 8939 (DetNet IP); the security considerations of all those documents apply equally here. No additional security considerations are introduced by this document.
DetNet MPLS over UDP/IP encapsulation layers, from bottom to top: Physical, Data-Link, IP Header, UDP Header, zero or more F-Labels, S-Label, DetNet Control Word (d-CW), and DetNet App-Flow Payload Packet. The MPLS DetNet encapsulation sits above the UDP/IP DetNet IP encapsulation.