| Internet-Draft | SIG | November 2024 |
| Ihle, et al. | Expires 26 May 2025 | [Page] |
TODO Abstract¶
This note is to be removed before publishing as an RFC.¶
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With the MPLS Network Action (MNA) framework, network actions are encoded in the MPLS stack. [I-D.ietf-mpls-mna-hdr] defines the encoding of such network actions and their data in the MPLS stack. These network actions are processed by all nodes on a path (hop-by-hop), by only selected nodes, or on an ingress-to-egress basis. LSRs have different capabilites that result from the available hardware resources. An ingress LER that pushes network actions to an MPLS stack MUST ensure that all nodes on the path can read and support the network actions. For that purpose, the MNA capabilities of an LSR need to be signaled to the ingress LER.¶
This document defines the required parameters of LSRs regarding their MNA capability and proposes a signaling extension using IGP such as IS-IS and OSPF.¶
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.¶
This document makes use of the terms defined in [I-D.ietf-mpls-mna-hdr] and in [I-D.ietf-mpls-mna-fwk].¶
In this section, the parameters an LSR SHOULD signal to the ingress LER to indicate its MNA capabilities are defined.¶
The readable label depth (RLD) is the number of LSEs an LSR can parse without performance impact[I-D.ietf-mpls-mna-fwk]. An LSR is required to search the MPLS stack for Network-Action Substacks (NAS) that have to be processed by this node. The ingress LER that pushes the network actions MUST ensure that a hop-by-hop-scoped network action is readable at each LSR on the path, i.e., that it is placed within the RLD of each node. For this purpose, multiple copies of the hop-by-hop-scoped NAS may be placed in the stack.¶
An example for the RLD parameter is given in Figure 1. With an RLD of 5, an LSR is capable of reading labels A, B, C, D, and E but not D. An RLD of 8 is required in this example to read the full MPLS stack.¶
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MPLS-Label = A | TC |0| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MPLS-Label = B | TC |0| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MPLS-Label = C | TC |0| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MPLS-Label = D | TC |0| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MPLS-Label = E | TC |0| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MPLS-Label = F | TC |0| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MPLS-Label = G | TC |0| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MPLS-Label = H | TC |1| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A NAS in the MNA header encoding is at least 2 LSEs and at most 17 LSEs large[I-D.ietf-mpls-mna-hdr]. At an LSR, at least two NAS, a select-scoped and a hop-by-hop-scoped NAS, are possible. With two maximum-sized NAS, an LSR is required to reserve 34 LSEs in hardware to be able to process network actions. This consumes hardware resources that may be needed to encode other LSEs, e.g., forwarding labels for SR-MPLS paths. Many use cases in the MNA framework[I-D.ietf-mpls-mna-use-cases] do not require a maximum-sized NAS of 17 LSEs to encode the network action and their ancillary data. Therefore, by signaling the maximum-supported NAS size of an MNA implementation from an LSR to an ingress LER, the allocated resources for NAS can be reduced and more resources are available for other purposes. An LSR SHOULD signal the maximum-supported size of a NAS for each scope, i.e., the parameters maxLSEs_NAS^Sel, maxLSEs_NAS^HBH, and maxLSEs_NAS^I2E. Those parameters include the Format A, B, C, and D LSEs from [I-D.ietf-mpls-mna-hdr] in a NAS. For select-scoped NAS, the ingress LER MUST NOT push NAS to the MPLS stack that exceed the MNA capabilities of the node the select-scoped NAS is destined for. For hop-by-hop-scoped NAS, the ingress LER MUST NOT push NAS to the MPLS stack that exceed the MNA capabilities of any node on the path. For I2E-scoped NAS, the ingress LER MUST NOT push NAS to the MPLS stack that exceed the MNA capabilities of the egress node.¶
Figure 1 illustrates the different NAS sizes in an MPLS stack that are signaled to the LSR. In this example, a select-scoped NAS has a maximum size of 4 LSEs, a hop-by-hop-scoped NAS of 7 LSEs, and an I2E-scoped NAS of 4 LSEs.¶
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MPLS-Label = A | TC |0| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ──┑ | MNA-Label=bSPL (TBA) | TC |0| TTL | │ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ │ | Opcode | Data |R|SEL|0|U| NASL=2|NAL=0| │ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ maxLSEs | Opcode | Data |0|U| Data |NAL=1| _NAS^Sel +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ │ |1| Data |0| Data | │ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ──┚ | MPLS-Label = B | TC |0| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MPLS-Label = C | TC |0| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ──┑ | MNA-Label=bSPL (TBA) | TC |0| TTL | │ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ │ | Opcode | Data |R|HBH|0|U| NASL=5|NAL=0| │ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ │ | Opcode | Data |0|U| Data |NAL=0| │ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ │ | Opcode | Data |0|U| Data |NAL=0| maxLSEs +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ _NAS^HBH | Opcode | Data |0|U| Data |NAL=0| │ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ │ | Opcode | Data |0|U| Data |NAL=1| │ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ │ |1| Data |0| Data | │ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ───┨ | MNA-Label=bSPL (TBA) | TC |0| TTL | │ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ │ | Opcode | Data |R|I2E|0|U| NASL=2|NAL=0| │ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ maxLSEs | Opcode | Data |0|U| Data |NAL=1| _NAS^I2E +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ │ |1| Data |1| Data | │ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ───┚
The security issues discussed in [I-D.ietf-mpls-mna-hdr] apply to this document.¶
This document has no IANA actions.¶
TODO acknowledge.¶