| Internet-Draft | MPLS Inspection MSD | September 2023 |
| Liu | Expires 21 March 2024 | [Page] |
This document defines a new type of MSD to reflect the Readable Label Depth(RLD), and the mechanism to signal this MSD using IGP and BGP-LS.¶
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[I-D.ietf-mpls-mna-fwk] specifies an architectural framework for the MPLS Network Actions (MNA) technologies. MNA technologies are used to indicate actions for Label Switched Paths (LSPs) and/or MPLS packets and to transfer data needed for these actions. And an MNA solution is envisioned as a set of network action sub-stacks(NAS), plus possible post-stack data. In order to put the NAS(s) at the appropriate place into the MPLS label stack, [I-D.ietf-mpls-mna-fwk] introduces the concept of Readable Label Depth(RLD), and puts forward the need for signaling of RLD via MPLS signaling protocols.¶
Maximum SID Depth (MSD)[RFC8491] is originally introduced for SR-MPLS to express the number of SIDs supported by a node or a link on a node. In a non-SR MPLS network, MSD defines the maximum label depth.¶
This document defines a new type of MSD for RLD, and the mechanism to signal this MSD using IGP and BGP-LS.¶
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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
MNA: MPLS Network Actions¶
NAS: Network Action ub-stack¶
EL: Entropy Label¶
ERLD: Entropy Readable Label Depth¶
RLD: Readable Label Depth¶
The RLD MSD MAY be used by NAS imposing node to determine the position of the NAS. When the label stacks are determined by a centralized controller, the RLD MSD of each intermediate LSR SHOULD be sent to the controller.¶
With RLD MSD, new application/network action-specified MSDs analogous to ERLD-MSD[RFC9088] [RFC9089] MAY not be needed. For example, a node can signal certain network action capability and the RLD MSD to indicate that it can process this network action within the MSD.¶
Editor's note: The reason why ERLD-MSD is not reused to reflect the RLD is that the definition of ERLD is strongly related the router's ability to process entropy label. As specified in [RFC8662], the ERLD means that the router will perform load-balancing using the EL if the EL is placed within the first ERLD labels, and a router capable of reading N labels but not using an EL located within those N labels MUST consider its ERLD to be 0. Considering that implementations in strict accordance with the definition of ERLD may exist, defining a new MSD instead of reusing/updating ERLD is preferred in this document.¶
A new IGP MSD-Type, called RLD MSD, is defined. The MSD-Type code is to be assigned by IANA. The MSD-Value field is set to the maximum number of labels a router can read in the range between 0 to 255. The scope of the advertisement depends on the application. This MSD can be advertised on the per-node and/or per-link basis as in IS-IS [RFC8491] and OSPF [RFC8476].¶
The absence of RLD MSD advertisements indicates only that the advertising node does not support advertisement of this capability.¶
The IGP extensions defined in this document can be advertised via BGP-LS (distribution of Link-State and TE information using BGP) [RFC7752] using existing BGP-LS TLVs.¶
The RLD MSD is advertised via the Node MSD TLV and/or the Link MSD TLV as defined in [RFC8814].¶
This document specifies the ability to advertise additional node capabilities using IS-IS, OSPF and BGP-LS. As such, the security considerations as described in [RFC5340], [RFC7684], [RFC7752], [RFC7770], [RFC7794], [RFC7981], [RFC8476], [RFC8491], [RFC8662], [RFC8814], [RFC9085] are applicable to this document.¶
Incorrectly setting of the RLD MSD value may lead to poor or no execution of the network action.¶
This document requests the following allocation from IANA:¶
Type TBA in the IGP MSD-Types registry is requested to be assigned for RLD MSD.¶
The author would like to thank Greg Mirsky, Les Ginsberg, Tony Li and Gyan Mishra for their helpful review and comments.¶