RFC 8149

RSVP Extensions for Reoptimization of Loosely Routed Point-to-Multipoint Traffic Engineering Label Switched Paths (LSPs)

📅 published April 2017, from ietf

RFC 8149: RSVP Extensions for Reoptimization of Loosely Routed Point-to-Multipoint Traffic Engineering Label Switched Paths (LSPs) 🦋

Title block tea ☕

  • Series: IETF, Request for Comments: 8149
  • Authors: T. Saad, Ed.; R. Gandhi, Ed.; Z. Ali (Cisco Systems, Inc.); R. Venator (Defense Information Systems Agency); Y. Kamite (NTT Communications Corporation)
  • Category: Standards Track ✨
  • ISSN: 2070-1721
  • Date: April 2017
  • Obsoletes / Updates: the title block doesn't list any RFCs this one obsoletes or updates 🙈

Abstract ✨

Okay bestie, the reoptimization of a Point-to-Multipoint (P2MP) Traffic Engineering (TE) Label Switched Path (LSP) can be triggered in a few ways. You can reoptimize one individual source-to-leaf (S2L) sub-LSP, or a set of S2L sub-LSPs, both using the Sub-Group-based reoptimization method. Or you can redo the whole P2MP-TE LSP tree using the Make-Before-Break (MBB) method. 💅

This document takes the existing tools for reoptimizing loosely routed Point-to-Point (P2P) TE LSPs, checks how they hold up when applied to P2MP-TE LSPs, points out the problems, and defines procedures to fix them. 🔥 When you reoptimize a ton of S2L sub-LSPs in one tree with the Sub-Group-based method, the S2L sub-LSP descriptor list might need to be semantically fragmented, which is a big mood. So the doc defines a fragment identifier that helps recipient nodes unambiguously put the fragmented S2L sub-LSP descriptor list back together. 🧩

Status of This Memo ✨

This is an Internet Standards Track document. 🌸

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. 📚

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc8149. 🔗

Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved. 🎀

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, because they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions, and they are provided without warranty as described in the Simplified BSD License. 💜

Table of Contents 🧭

1. Introduction ....................................................3
2. Conventions Used in This Document ...............................4
   2.1. Key Word Definitions .......................................4
   2.2. Abbreviations ..............................................4
   2.3. Terminology ................................................4
3. Overview ........................................................5
   3.1. Loosely Routed Inter-domain P2MP-TE LSP Tree ...............5
   3.2. Existing Mechanism for Tree-Based P2MP-TE LSP
        Reoptimization .............................................6
   3.3. Existing Mechanism for Sub-Group-Based P2MP-TE LSP
        Reoptimization .............................................7
4. Signaling Extensions for Loosely Routed P2MP-TE LSP
   Reoptimization ..................................................8
   4.1. Tree-Based Reoptimization ..................................8
   4.2. Sub-Group-Based Reoptimization Using Fragment Identifier ...9
5. Message and Object Definitions .................................11
   5.1. "P2MP-TE Tree Re-evaluation Request" Flag .................11
   5.2. "Preferable P2MP-TE Tree Exists" Path Error Sub-code ......11
   5.3. Fragment Identifier for S2L Sub-LSP Descriptor ............11
6. Compatibility ..................................................12
7. IANA Considerations ............................................13
   7.1. "P2MP-TE Tree Re-evaluation Request" Flag .................13
   7.2. "Preferable P2MP-TE Tree Exists" Path Error Sub-code ......13
   7.3. Fragment Identifier for S2L Sub-LSP Descriptor ............14
8. Security Considerations ........................................14
9. References .....................................................15
   9.1. Normative References ......................................15
   9.2. Informative References ....................................16
Acknowledgments ...................................................16
Authors' Addresses ................................................17

1. Introduction 🌈

This document defines Resource Reservation Protocol - Traffic Engineering (RSVP-TE) [RFC2205] [RFC3209] signaling extensions for reoptimizing loosely routed Point-to-Multipoint (P2MP) Traffic Engineering (TE) Label Switched Paths (LSPs) [RFC4875] in a Multiprotocol Label Switching (MPLS) or Generalized MPLS (GMPLS) [RFC3473] network. ✨

A P2MP-TE LSP is made up of one or more source-to-leaf (S2L) sub-LSPs. 🦋 A loosely routed P2MP-TE S2L sub-LSP is one whose path does not contain the full explicit route that identifies each node along the path to the egress node at the time the ingress node signals it. Such an S2L sub-LSP is signaled with no Explicit Route Object (ERO) [RFC3209], with an ERO that contains at least one "loose next hop", or with an ERO that contains an abstract node that identifies more than one node. This is often the case with inter-domain P2MP-TE LSPs where a Path Computation Element (PCE) is not used [RFC5440]. 🧠

As per [RFC4875], an ingress node may reoptimize the entire P2MP-TE LSP tree by re-signaling all of its S2L sub-LSPs using the Make-Before-Break (MBB) method. Or it may reoptimize an individual S2L sub-LSP or a set of S2L sub-LSPs (in other words, an individual destination or a set of destinations), both using the Sub-Group-based reoptimization method. 🎯

[RFC4736] defines an RSVP signaling procedure for reoptimizing the path(s) of loosely routed Point-to-Point (P2P) TE LSP(s). The mechanisms listed in [RFC4736] include a way for the ingress node to trigger a new path re-evaluation request, and a way for the midpoint node to send a notification about a preferred path being available. This document looks at how those mechanisms apply to reoptimizing loosely routed P2MP-TE LSPs, identifies the issues that come up, and defines procedures to address them. 💅

For reoptimizing a group of S2L sub-LSPs in a tree using the Sub-Group-based reoptimization method, an S2L sub-LSP descriptor list can be used to signal one or more S2L sub-LSPs in an RSVP message. This RSVP message may need to be semantically fragmented when a large number of S2L sub-LSPs are added to the descriptor list. So this document defines the notion of a fragment identifier to help recipient nodes unambiguously reconstruct the fragmented S2L sub-LSP descriptor list. 🧩

2. Conventions Used in This Document 📖

2.1. Key Word Definitions 🔑

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]. 🫶

2.2. Abbreviations 🔤

  • ABR: Area Border Router.
  • ERO: Explicit Route Object.
  • LSP: Label Switched Path.
  • LSR: Label Switching Router.
  • RRO: Record Route Object.
  • S2L sub-LSP: Source-to-leaf sub-LSP.
  • TE LSP: Traffic Engineering LSP.

2.3. Terminology 🧃

This document defines the following terms:

  • Ingress node: Head-end / source node of the TE LSP.
  • Egress node: Tail-end / destination node of the TE LSP.

It is assumed that the reader is also familiar with the terminology in [RFC4736] and [RFC4875]. 🤓

3. Overview 🗺️

[RFC4736] defines RSVP signaling extensions for reoptimizing loosely routed P2P TE LSPs as follows: 💜

  • A midpoint LSR that expands loose next hop(s) sends a solicited or unsolicited PathErr with Notify error code 25 (as defined in [RFC3209]), with sub-code 6 to indicate "Preferable Path Exists" to the ingress node.
  • An ingress node triggers a path re-evaluation request at all midpoint LSRs that expand loose next hop(s) by setting the "Path Re-evaluation Request" flag (0x20) in the SESSION_ATTRIBUTES object in the Path message.
  • The ingress node, upon receiving this PathErr with the Notify error code (either solicited or unsolicited), initiates the reoptimization of the LSP, using the MBB method with a different LSP-ID.

The following sections discuss the issues that may arise when applying the mechanisms defined in [RFC4736] for reoptimizing loosely routed P2MP-TE LSPs. 👀

3.1. Loosely Routed Inter-domain P2MP-TE LSP Tree 🌳

An example of a loosely routed inter-domain P2MP-TE LSP tree is shown in Figure 1. In this example, the P2MP-TE LSP tree consists of three S2L sub-LSPs, to destinations (i.e., leafs) R10, R11, and R12 from the ingress node (i.e., source) R1. Nodes R2 and R5 are branch nodes, and nodes ABR3, ABR4, ABR7, ABR8, and ABR9 are ABRs. For the S2L sub-LSP to destination R10, nodes ABR3, ABR7, and R10 are defined as loose next hops. For the S2L sub-LSP to destination R11, nodes ABR3, ABR8, and R11 are defined as loose next hops. For the S2L sub-LSP to destination R12, nodes ABR4, ABR9, and R12 are defined as loose next hops. 🦋

      <--area1--><--area0--><-area2->

                           ABR7---R10
                          /
                         /
                ABR3---R5
               /         \
              /           \
       R1---R2             ABR8---R11
              \
               \
                ABR4---R6
                         \
                          \
                           ABR9---R12

Figure 1: Example of Loosely Routed Inter-domain P2MP-TE LSP Tree 🌸

3.2. Existing Mechanism for Tree-Based P2MP-TE LSP Reoptimization 🌸

okay so, the mechanisms in [RFC4736] are honestly super easy to use when you want to reoptimize one S2L sub-LSP or a whole group of them 💅. BUT if you want to reoptimize an entire P2MP-TE LSP tree with those same tools, things get messy fast. The ingress node would have to send path re-evaluation requests on all of the S2L sub-LSPs (we're talking typically hundreds 😭), and the midpoint LSR would have to send PathErrs with the Notify error code for every single one of them. Bestie, that is a LOT of signaling. 🫠 And it causes some real drama:

  • A midpoint LSR that expands loose next hop(s) might have to collect all the path re-evaluation requests for every S2L sub-LSP (say, by waiting on a timer) and treat them as one reoptimization request for the whole tree. If it doesn't, it might jump the gun and send a "Preferable Path Exists" notification for just one S2L sub-LSP or a little subset of them. Not the vibe 🙈
  • The ingress node has the same problem. It has to guess whether it should reoptimize the whole tree or just some S2L sub-LSPs. For example, an implementation could wait long enough to hear back from every PathErr. But timer-based procedures like that can give undesired results 😬
  • The ingress node that gets (un)solicited PathErr(s) with the Notify error code for one or more individual S2L sub-LSPs might start reoptimizing just that subset too early. As [RFC4875], Section 14.2 mentions, this Sub-Group-based reoptimization can cause data duplication. That duplication could be avoided if the entire P2MP-TE LSP tree gets reoptimized using the MBB method with a different LSP-ID, especially once the ingress node has PathErrs with the Notify error code for all S2L sub-LSPs of the tree 🎀

So to fix all of this and line P2MP-TE reoptimization up with P2P LSPs ([RFC4736]), we need a way to reoptimize the whole LSP tree by re-signaling all S2L sub-LSPs with a different LSP-ID ✨. That's exactly what this document is for. It defines RSVP-TE signaling extensions so that:

  • the ingress node can trigger re-evaluation of the P2MP LSP tree on every hop that has a next hop defined as a loose or abstract hop for one or more S2L sub-LSP paths, and
  • a midpoint LSR can tell the ingress node that a preferable LSP tree exists (compared to the current path), or that the whole P2MP-TE LSP has to be reoptimized (because maintenance is needed on the TE LSP path) 🦋

(See Section 4.1.)

3.3. Existing Mechanism for Sub-Group-Based P2MP-TE LSP Reoptimization 💖

Okay, so you can combine the procedures from [RFC4736] with the Sub-Group-based reoptimization procedures from [RFC4875], Section 14.2. When you do, an ingress node MAY trigger path re-evaluation requests for a whole set of S2L sub-LSPs in a single Path message, using an S2L sub-LSP descriptor list 🧚. Then a midpoint LSR can send a PathErr with Notify error code 25 and sub-code 6 ("Preferable Path Exists") that lists the S2L sub-LSPs passing through it, again using an S2L sub-LSP descriptor list, to let the ingress node know.

This is lowkey a great way to reoptimize a sub-group of S2L sub-LSPs inside an LSP tree that uses the same LSP-ID 🍓. It also helps with the scaling problem of sending RSVP messages for every individual S2L sub-LSP. BUT, when you try to use it to reoptimize the whole tree, a few issues pop up:

  • A Path message that's supposed to carry the path re-evaluation request from [RFC4736] with a full list of S2L sub-LSPs in its S2L sub-LSP descriptor list gets split up at branching LSRs. Only the subset of S2L sub-LSPs routed over the same next hop ends up in the descriptor list of the Path message that goes on to downstream midpoint LSRs. So when a preferable path exists at one of those midpoint LSRs, the PathErr with the Notify error code can only include the S2L sub-LSPs that go through that LSR. At that point, the ingress node has no way to tell which kind of reoptimization to run: Sub-Group-based reoptimization using the same LSP-ID, or tree-based reoptimization using a different LSP-ID 😭
  • An LSR may semantically fragment a large RSVP message (when the combined message isn't big enough to fit all the S2L sub-LSPs). Then the ingress node might get several PathErrs, each with a subset of S2L sub-LSPs (either because the combined Path message got fragmented or because the combined PathErr message got fragmented). It would need extra logic to figure out how to reoptimize the LSP tree, like waiting a while to gather every PathErr before doing anything 🙃. And when fragments show up, they can arrive out of order, and the receiver has no way of knowing where the S2L sub-LSP list begins and ends.

To fix these fragmentation issues, this document defines a new fragment identifier object for the S2L sub-LSP descriptor list, used when a large number of S2L sub-LSPs get combined into one RSVP message (see Section 4.2). ✨

4. Signaling Extensions for Loosely Routed P2MP-TE LSP Reoptimization 👑

4.1. Tree-Based Reoptimization 🌈

okay, so to evaluate a P2MP-TE LSP tree on midpoint LSRs that expand loose next hop(s), an ingress node MAY send a Path message with the "P2MP-TE Tree Re-evaluation Request" flag set (bit number 14 in the Attribute Flags TLV), as defined in this document 💅. The ingress node picks one of the S2L sub-LSPs of the P2MP-TE LSP tree that transits a midpoint LSR to trigger the re-evaluation request. The ingress node MAY also send a re-evaluation request to each border LSR on the path of the LSP tree 🫶.

So when a midpoint LSR that expands loose next hop(s) for one or more S2L sub-LSP paths gets a Path message with the "P2MP-TE Tree Re-evaluation Request" flag set, here's what it does:

  • The midpoint LSR MUST check for a preferable P2MP-TE LSP tree by re-evaluating all S2L sub-LSPs that are expanded paths of the loose next hops of the P2MP-TE LSP. No skipping, bestie 🧐
  • If a preferable P2MP-TE LSP tree is found, the midpoint LSR MUST send the ingress node an RSVP PathErr with Notify error code 25 [RFC3209] and sub-code 13 ("Preferable P2MP-TE Tree Exists)" as defined in this document. After that, the midpoint LSR SHOULD NOT propagate the "P2MP-TE Tree Re-evaluation Request" flag in the subsequent RSVP Path messages it sends downstream for the re-evaluated P2MP-TE LSP 🌸.
  • If no preferable tree for P2MP-TE LSPs can be found, the midpoint LSR that expands loose next hop(s) for one or more S2L sub-LSP paths MUST propagate the request downstream by setting the "P2MP-TE Tree Re-evaluation Request" flag in the LSP_ATTRIBUTES object of the RSVP Path message 🦋.

A midpoint LSR MAY send an unsolicited PathErr with the Notify error code and the "Preferable P2MP-TE Tree Exists" sub-code to the ingress node, to let it know about a preferred P2MP-TE LSP tree when it determines one exists. In that case, the midpoint LSR that expands loose next hop(s) for one or more S2L sub-LSP paths picks one of the S2L sub-LSPs of the P2MP-TE LSP tree to send this PathErr message to the ingress node. The midpoint LSR SHOULD think about how often it sends such a PathErr, since (1) a PathErr may get lost on its way to the ingress node, and (2) the ingress node may choose not to reoptimize the LSP when it receives one 🙈.

Sending an RSVP PathErr with the Notify error code and the "Preferable P2MP-TE Tree Exists" sub-code to the ingress node tells it that a preferable P2MP-TE LSP tree exists. When the ingress node gets this PathErr, it SHOULD trigger reoptimization of the LSP, using the MBB method with a different LSP-ID 🎀✨

4.2. Sub-Group-Based Reoptimization Using Fragment Identifier 🦋

okay so, it might be preferable (per [RFC4875]) to reoptimize the entire P2MP-TE LSP by re-signaling all of its S2L sub-LSPs (Section 14.1 ("Make-before-Break") in [RFC4875]). Or you can reoptimize just one S2L sub-LSP, or a group of them, meaning an individual destination or a group of destinations (Section 14.2 ("Sub-Group-Based Re-Optimization") in [RFC4875]). Both of these use the same LSP-ID 💅. For loosely routed S2L sub-LSPs, you can do this with the procedures defined in [RFC4736] to reoptimize one or more S2L sub-LSPs of the P2MP-TE LSP 🫶

an ingress node can trigger path re-evaluation requests using the procedures defined in [RFC4736] for a set of S2L sub-LSPs. It does this by combining multiple Path messages using an S2L sub-LSP descriptor list [RFC4875]. That descriptor list is built from a series of S2L_SUB_LSP objects, as defined in [RFC4875]. 🧩 Same energy from the other side: a midpoint LSR may send a PathErr with Notify error code 25 and sub-code 6 ("Preferable Path Exists"). That PathErr contains a list of the S2L sub-LSPs transiting through the LSR, using an S2L sub-LSP descriptor list, so the ingress node knows about the preferable paths available 👀

the S2L_SUB_LSP_FRAG object defined in this document is optional, with the following exceptions:

  • As per [RFC4875], Section 5.2.3 ("Transit Fragmentation of Path State Information"), when a Path message is not large enough to fit all S2L sub-LSPs in the descriptor list, an LSR may semantically fragment the message. In this case, the LSR MUST add the S2L_SUB_LSP_FRAG object defined in this document for each fragment in the S2L sub-LSP descriptor. That's how it can rebuild the list from the received fragments, even if they show up out of order 😭
  • In any other situation where an RSVP message needs to be fragmented, an LSR MUST add the S2L_SUB_LSP_FRAG object for each fragment in the S2L sub-LSP descriptor. 💖

a midpoint LSR SHOULD wait to accumulate all S2L sub-LSPs before attempting to re-evaluate a preferable path when a Path message for "Path Re-evaluation Request" arrives with the S2L_SUB_LSP_FRAG object. If a midpoint LSR does not receive all fragments of the Path message within a configurable time interval (for example, because fragments got lost), it SHOULD trigger the re-evaluation of all S2L sub-LSPs of the P2MP-TE LSP transiting on the node. Just know that a midpoint LSR MUST receive at least one fragment of the Path message to trigger this behavior 🍓

an ingress node SHOULD wait to accumulate all S2L sub-LSPs before attempting to trigger reoptimization when a PathErr with the Notify error code and the "Preferable Path Exists" sub-code shows up with an S2L_SUB_LSP_FRAG object. If an ingress node does not receive all fragments of the PathErr message within a configurable time interval (for example, when fragments are lost), it SHOULD trigger the reoptimization of all S2L sub-LSPs of the P2MP-TE LSP transiting on the midpoint node that sent the PathErr message. An ingress node MUST receive at least one fragment of the PathErr message to trigger this behavior 🌸

the S2L_SUB_LSP_FRAG object defined in this document has a wider applicability beyond P2MP-TE LSP reoptimization. It can also be used (in Path and Resv messages) to set up a new P2MP-TE LSP, and to send other PathErr messages as well as Path Tear and Resv Tear messages for a set of S2L sub-LSPs. That's outside the scope of this document, so it's a whole other slay for another day 💅✨

5. Message and Object Definitions 🧚

5.1. "P2MP-TE Tree Re-evaluation Request" Flag 🎀

so to trigger a tree re-evaluation request, this document defines a new flag in the Attribute Flags TLV of the LSP_ATTRIBUTES object [RFC5420]:

Bit Number 14: "P2MP-TE Tree Re-evaluation Request" flag

the "P2MP-TE Tree Re-evaluation Request" flag is meaningful in a Path message of a P2MP-TE S2L sub-LSP. The ingress node inserts it using the message format defined in [RFC6510] 💜

5.2. "Preferable P2MP-TE Tree Exists" Path Error Sub-code 🔥

to tell an ingress node that a preferable P2MP-TE LSP tree exists, this document defines a new sub-code for PathErr messages with Notify error code 25 [RFC3209]:

Sub-code 13: "Preferable P2MP-TE Tree Exists" sub-code

when a preferable path for a P2MP-TE LSP tree exists, the midpoint LSR sends a solicited or unsolicited "Preferable P2MP-TE Tree Exists" sub-code with a PathErr message (Notify error code 25) to the ingress node of the P2MP-TE LSP. Main character energy, honestly 👑

5.3. Fragment Identifier for S2L Sub-LSP Descriptor 🌈

the S2L_SUB_LSP object [RFC4875] identifies a particular S2L sub-LSP belonging to the P2MP-TE LSP. An S2L sub-LSP descriptor list is created using a series of S2L_SUB_LSP objects, as defined in [RFC4875]. The RSVP message might need to be semantically fragmented [RFC4875] because there are a lot of S2L sub-LSPs in the descriptor list, and those fragments can arrive out of order. So to rebuild the fragmented S2L sub-LSP descriptor list correctly, this document defines the following object to identify the fragments 🦋

S2L_SUB_LSP_FRAG: Class Number 204

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Length (8 bytes)     | Class Num 204 |   C-Type 1    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Fragment ID        | Fragments Tot.| Fragment Num. |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Fragment ID: 16-bit integer in the range of 1 to 65535.

This value increments for each new RSVP message that needs to be semantically fragmented. The fragment ID resets to 1 when it reaches the maximum value of 65535. The scope of the fragment ID is limited to the RSVP message type (e.g., Path) carrying the fragment. In other words, fragment IDs have no correlation between different RSVP message types (e.g., Path and PathErr). The receiver does not check that consecutive new RSVP messages (e.g., Path messages) arrive with fragment IDs incremented by 1. No stress, the receiver just doesn't check 🙈

Fragments Total: 8-bit integer in the range of 1 to 255.

This value indicates the number of fragments sent for the given RSVP message. This value MUST be the same in all fragmented RSVP messages with a common fragment ID. Non-negotiable, bestie 💅

Fragment Number: 8-bit integer in the range of 1 to 255.

This value indicates the position of this fragment in the given RSVP message 🧚

the format of an S2L sub-LSP descriptor message is as follows:

<S2L sub-LSP descriptor> ::=
                 [ <S2L_SUB_LSP_FRAG> ]
                   <S2L_SUB_LSP>
                 [ <P2MP SECONDARY_EXPLICIT_ROUTE> ]

the S2L_SUB_LSP_FRAG object is added before the S2L_SUB_LSP object in the semantically fragmented RSVP message. Order matters, babe 🍓

6. Compatibility 🫧

the LSP_ATTRIBUTES object was defined in [RFC5420], and its message formats in [RFC6510], with class numbers in the form 11bbbbbb. That's what keeps it compatible with nodes that don't support this extension. Per [RFC2205], nodes that don't support this extension ignore the new flag defined for this object in this document and forward it without modification 💖

the S2L_SUB_LSP_FRAG object has class numbers in the form 11bbbbbb too, so it's also compatible with non-supporting nodes. Per [RFC2205], nodes that don't support this object ignore it and forward it without modification 🌸

7. IANA Considerations 📋

IANA has performed the actions described below. Let's go 🔥

7.1. "P2MP-TE Tree Re-evaluation Request" Flag ✨

IANA maintains the "Resource Reservation Protocol-Traffic Engineering (RSVP-TE) Parameters" registry (see <http://www.iana.org/assignments/rsvp-te-parameters>). Per Section 5.1 of this document, IANA has registered a new flag in the "Attribute Flags" registry. This new flag is defined for the Attribute Flags TLV in the LSP_ATTRIBUTES object [RFC5420].

+-----+---------------+----------+----------+-----+-----+-----------+
| Bit | Name          | Attribute| Attribute| RRO | ERO | Reference |
| No  |               | Flags    | Flags    |     |     |           |
|     |               | Path     | Resv     |     |     |           |
+-----+---------------+----------+----------+-----+-----+-----------+
|     | P2MP-TE Tree  | Yes      | No       | No  | No  | This      |
| 14  | Re-evaluation |          |          |     |     | document  |
|     | Request       |          |          |     |     |           |
+-----+---------------+----------+----------+-----+-----+-----------+

7.2. "Preferable P2MP-TE Tree Exists" Path Error Sub-code 🎀

IANA maintains the "Resource Reservation Protocol (RSVP) Parameters" registry (see <http://www.iana.org/assignments/rsvp-parameters>). Per Section 5.2 of this document, IANA has registered a new error code in the "Sub-Codes - 25 Notify Error" sub-registry of the "Error Codes and Globally-Defined Error Value Sub-Codes" registry.

As defined in [RFC3209], error code 25 in the ERROR_SPEC object corresponds to a PathErr with the Notify error. This document adds a new "Preferable P2MP-TE Tree Exists" sub-code for this PathErr, as follows:

+----------+--------------------+---------+---------+-----------+
| Value    | Description        | PathErr | PathErr | Reference |
|          |                    | Code    | Name    |           |
+----------+--------------------+---------+---------+-----------+
|  13      | Preferable P2MP-TE | 25      | Notify  | This      |
|          | Tree Exists        |         | Error   | document  |
+----------+--------------------+---------+---------+-----------+

7.3. Fragment Identifier for S2L Sub-LSP Descriptor 🧁

IANA maintains the "Resource Reservation Protocol (RSVP) Parameters" registry (see <http://www.iana.org/assignments/rsvp-parameters>). Per Section 5.3 of this document, IANA has registered a new class number in the "Class Names, Class Numbers, and Class Types" registry.

+-----------------+---------------------------+-----------------+
| Class Number    | Class Name                | Reference       |
+-----------------+---------------------------+-----------------+
| 204             | S2L_SUB_LSP_FRAG          | This document   |
+-----------------+---------------------------+-----------------+

IANA has also created the "Class Types or C-Types - 204 S2L_SUB_LSP_FRAG" registry and populated it as follows:

+-----------------+---------------------------+-----------------+
| Value           | Description               | Reference       |
+-----------------+---------------------------+-----------------+
| 1               | S2L_SUB_LSP_FRAG          | This document   |
+-----------------+---------------------------+-----------------+

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8.  Security Considerations

   This document defines RSVP-TE signaling extensions to allow an
   ingress node of a P2MP-TE LSP to request the re-evaluation of the LSP
   tree downstream of a node and to allow a midpoint LSR to notify the
   ingress node of the existence of a preferable tree by sending a
   PathErr message.  As per [RFC4736], in the case of a P2MP-TE LSP S2L
   sub-LSP spanning multiple domains, it may be desirable for a midpoint
   LSR to modify the RSVP PathErr message to preserve confidentiality
   across domains.

   This document also defines a fragment identifier for the S2L sub-LSP
   descriptor when combining a large number of S2L sub-LSPs in an RSVP
   message and the message needs to be semantically fragmented.  The
   introduction of the fragment identifier, by itself, introduces no
   additional information to signaling.  For a general discussion on
   security issues related to MPLS and GMPLS, see the MPLS/GMPLS
   security framework [RFC5920].

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2205]  Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, DOI 10.17487/RFC2205,
              September 1997, <http://www.rfc-editor.org/info/rfc2205>.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <http://www.rfc-editor.org/info/rfc3209>.

   [RFC4736]  Vasseur, JP., Ed., Ikejiri, Y., and R. Zhang,
              "Reoptimization of Multiprotocol Label Switching (MPLS)
              Traffic Engineering (TE) Loosely Routed Label Switched
              Path (LSP)", RFC 4736, DOI 10.17487/RFC4736,
              November 2006, <http://www.rfc-editor.org/info/rfc4736>.

   [RFC4875]  Aggarwal, R., Ed., Papadimitriou, D., Ed., and S.
              Yasukawa, Ed., "Extensions to Resource Reservation
              Protocol - Traffic Engineering (RSVP-TE) for
              Point-to-Multipoint TE Label Switched Paths (LSPs)",
              RFC 4875, DOI 10.17487/RFC4875, May 2007,
              <http://www.rfc-editor.org/info/rfc4875>.

   [RFC5420]  Farrel, A., Ed., Papadimitriou, D., Vasseur, JP., and A.
              Ayyangarps, "Encoding of Attributes for MPLS LSP
              Establishment Using Resource Reservation Protocol Traffic
              Engineering (RSVP-TE)", RFC 5420, DOI 10.17487/RFC5420,
              February 2009, <http://www.rfc-editor.org/info/rfc5420>.

9.2.  Informative References

   [RFC3473]  Berger, L., Ed., "Generalized Multi-Protocol Label
              Switching (GMPLS) Signaling Resource ReserVation
              Protocol-Traffic Engineering (RSVP-TE) Extensions",
              RFC 3473, DOI 10.17487/RFC3473, January 2003,
              <http://www.rfc-editor.org/info/rfc3473>.

   [RFC5440]  Vasseur, JP., Ed., and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <http://www.rfc-editor.org/info/rfc5440>.

   [RFC5920]  Fang, L., Ed., "Security Framework for MPLS and GMPLS
              Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
              <http://www.rfc-editor.org/info/rfc5920>.

   [RFC6510]  Berger, L. and G. Swallow, "Resource Reservation Protocol
              (RSVP) Message Formats for Label Switched Path (LSP)
              Attributes Objects", RFC 6510, DOI 10.17487/RFC6510,
              February 2012, <http://www.rfc-editor.org/info/rfc6510>.

Acknowledgments

   The authors would like to thank Loa Andersson, Sriganesh Kini, Curtis
   Villamizar, Dimitri Papadimitriou, Nobo Akiya, Vishnu Pavan Beeram,
   and Joel M. Halpern for reviewing this document and providing many
   useful comments and suggestions.  The authors would also like to
   thank Ling Zeng with Cisco Systems for implementing the mechanisms
   defined in this document.  A special thanks to Adrian Farrel for his
   thorough review of this document.

Authors' Addresses

   Tarek Saad (editor)
   Cisco Systems, Inc.

   Email: tsaad@cisco.com


   Rakesh Gandhi (editor)
   Cisco Systems, Inc.

   Email: rgandhi@cisco.com


   Zafar Ali
   Cisco Systems, Inc.

   Email: zali@cisco.com


   Robert H. Venator
   Defense Information Systems Agency

   Email: robert.h.venator.civ@mail.mil


   Yuji Kamite
   NTT Communications Corporation

   Email: y.kamite@ntt.com
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