RFC 7715

Multipoint LDP (mLDP) Node Protection

📅 published January 2016, from ietf

📜 RFC 7715: Multipoint LDP (mLDP) Node Protection 🎀

Okay bestie, let's get into it ✨ This one is from the IETF, and it's a Standards Track document, so yes, it's the real deal 💅 It was published in January 2016 and it's part of the ISSN: 2070-1721 series. 🌸

The editor is IJ. Wijnands, Ed. (Ed. means editor 🫶), with co-authors K. Raza from Cisco Systems, Inc., A. Atlas from Juniper Networks, Inc., J. Tantsura from Ericsson, and Q. Zhao from Huawei Technology. That's a whole squad 👑

Nothing in the title block says it obsoletes or updates another RFC, so this one stands on its own 🦋

Hold up, the Status line is key here: this is an Internet Standards Track document, which means the IETF community reviewed it and the IESG approved it for publication. Lowkey the most official kind of RFC 🔥

Abstract

Okay so the whole point of this doc is node protection for P2MP and MP2MP LSPs that were built using mLDP. 🧚 Here's the vibe: if a node N dies, you need traffic to have somewhere else to go. The PLR LSR (Point of Local Repair) of node N has to learn about the MPT LSR(s) (Merge Point) of node N, so it can redirect traffic to them when N fails 💖

The redirect depends on existing P2P LSPs that start at the PLR and end at the MPT LSRs, and they route around LSR N completely 🦋

It's giving redundancy, no cap 🌈

Status of This Memo

Bestie, this section is the boring-but-important legal stuff 📜 It says this is an Internet Standards Track document, it's a product of the IETF, and it went through public review and got approved by the IESG. You can find more on Internet Standards in Section 2 of RFC 5741 📚

The current status, errata, and feedback info live at http://www.rfc-editor.org/info/rfc7715 🔗

Copyright Notice

The doc is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents, which you can read at http://trustee.ietf.org/license-info 🌸 Please actually read these, because they explain your rights and restrictions. Any Code Components pulled out of this document need to include Simplified BSD License text, as described in Section 4.e of the Trust Legal Provisions, and they come without warranty as described in the Simplified BSD License ⚠️

1. Introduction (page 3)
- 1.1. Conventions Used in This Document (page 3)
- 1.2. Terminology (page 4)
2. PLR Determination (page 4)
- 2.1. Transit Node Procedure (page 5)
- 2.2. MP2MP Root Node Procedure (page 6)
- 2.3. PLR Information Encoding (page 7)
3. Using the tLDP Session (page 9)
4. Link or Node Failure (page 10)
- 4.1. Reconvergence after Node or Link Failure (page 11)
  - 4.1.1. Node Failure (page 12)
  - 4.1.2. Link Failure (page 12)
  - 4.1.3. Switching to New Primary Path (page 12)
5. mLDP Capabilities for Node Protection (page 13)
- 5.1. PLR Capability (page 13)
- 5.2. MPT Capability (page 14)
- 5.3. The Protected LSR (page 14)
- 5.4. The Node Protection Capability (page 15)
6. Security Considerations (page 16)
7. IANA Considerations (page 16)
8. References (page 17)
- 8.1. Normative References (page 17)
- 8.2. Informative References (page 17)
Acknowledgments (page 18)
Contributors (page 18)
Authors' Addresses (page 19)

1. Introduction ✨

Okay so the big idea here is the same as the abstract: node protection for P2MP and MP2MP LSPs built by mLDP [RFC6388] 🧚 If node N goes down, the PLR LSR of N needs to know the MPT LSR(s) of N so traffic can be redirected to them 💖 The redirect uses existing P2P LSPs, which start at the PLR, end at the MPT LSRs, and skip LSR N entirely 🦋

Now the spec doesn't define how to set up those P2P LSPs. That's out of scope 🙈 But you could totally imagine using RSVP-TE [RFC5420] or LDP Loop-Free Alternate (LFA) [RFC5286] to make them happen 🌸

Here's the solution in a nutshell: the MPT LSR(s) tell the PLR(s) via signaling over a Targeted LDP (tLDP) session [RFC7060] 💅 Having a tLDP session with the PLR means you don't need any extra procedures for Make-Before-Break (MBB), Graceful Restart (GR), or Typed Wildcard Forwarding Equivalence Class (FEC) 🎀 The catch is that you end up with additional tLDP sessions between each MPT and PLR LSR 😭

Now the requirements. The LSRs doing the PLR and MPT jobs, plus the protected node, MUST support what's in this document. Iykyk, that's the non-negotiable part 🔥 LDP capability negotiation [RFC5561] is how the nodes signal to each other that they've got this feature, and these nodes MUST support capability negotiation too 👑

1.1. Conventions Used in This Document 🌈

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 RFC 2119 [RFC2119] 💜

Also, "node" and "LSR" mean the same thing here 🧚 And "PLR" and "MPT" are just shorthand for "PLR LSR" and "MPT LSR" 🦋

1.2. Terminology 📚

mLDP: Multipoint LDP 🌸
PLR: Point of Local Repair. The LSR that redirects the traffic to one or more Merge Point LSRs 💖
MPT: Merge Point. The LSR that merges the backup LSP with the primary LSP. Heads up, there can be multiple MPT LSRs for a single MP-LSP node protection 👑
tLDP: Targeted LDP 🎀
MP LSP: Multi-Point LSP. Either a P2MP or MP2MP LSP ✨
root node: The root of either a P2MP or MP2MP LSP as defined in [RFC6388] 🫶

2. PLR Determination 🦋

So for an MPT to set up a tLDP session with a PLR, it first has to figure out who the PLR is for a particular MP LSP 🔥 It's the job of the protected node N to advertise the PLR's address to the MPT 💅

The PLR address for an MP LSP on node N is the address of the upstream LDP peer, but only when node N is NOT the root node of the MP2MP LSP 🙈 If the upstream LDP peer can't act as a PLR, then the procedures in this document don't apply and are out of scope 💀 If node N is the root node, things work a little differently, see Section 2.2 💖

The procedures assume all the participating nodes (N, PLRs, MPTs) are enabled (for example, by user configuration) to support and implement the PLR determination feature 🌈

Here's a big one: the procedures in this RFC require the protected node to be directly connected to the PLR and MPT nodes 😭 Why? Because mLDP relies on unicast routing to find the upstream LSR, and unicast routing (by default) only knows about the next hop, not beyond that 🧠 Supporting non-directly connected PLR and MPT nodes is outside the scope of this document 🙅‍♀️

2.1. Transit Node Procedure 🧚

Here's how it works when the protected node is a transit node on the path to the root 🌸

                    root
                     ^
                     |
                   (LSR1)
                  .  |  .
                 .   |   .
                .   (N)   .
                .   /  \  .
                 . /    \.
               (LSR2)  (LSR3)
                  |      |

           N: The node being protected.
           ...: Backup LSPs from LSR1 to LSR2 and LSR3.

                         Figure 1

So node N uses the root address of the MP LSP to figure out the upstream LSR for a given MP LSP, following the procedures in Section 2.4.1.1 of [RFC6388] 💅 In Figure 1, the upstream LSR is LSR1, because it's the first hop along the shortest path to the root address 🦋

Once N has the upstream LSR, it MUST advertise LSR1's address as the PLR address to the downstream members of the MP LSP (that's LSR2 and LSR3) 🔥 But only if the downstream member has announced support for node protection (see Section 5 for capability negotiation) 🫶 For the format and encoding of PLR address info, check Section 2.3 📚

Also, heads up: for the protected traffic to reach LSR2 and LSR3, LSR1 MUST have two unidirectional LSPs to LSR2 and LSR3 that bypass node N 🚨 Setting those up is outside the scope of this document 🙈

Part 1 of 4 is done, bestie 💖 Stay tuned for the next part, where we keep the good stuff coming ✨🎀

2.2. MP2MP Root Node Procedure

okay so this part is for when the protected node is the root of an MP2MP LSP 🌸 Check out figure 2 below, it's giving triangle vibes 🔺✨

                         |
                       (LSR1)
                      .  |  .
                     .   |   .
                    .   (N)   . root
                    .   /  \  .
                     . /    \.
                  (LSR2)....(LSR3)
                     |        |

               N: The MP2MP root node being protected.
               ...: Backup LSPs between LSR1, LSR2, and LSR3.

                             Figure 2

Assume that LSR1, LSR2, and LSR3 are all members of an MP2MP LSP where N is the root node 👑 Since N is the root, there is no upstream LSR and no single PLR LSR for protecting N, so that's the twist 🧚 To protect node N, all the directly connected members of the MP2MP have to show up and participate by acting as both PLR and MPT LSR 💅 An LSR acts as MPT for traffic coming from the other LSR(s), and it acts as PLR for traffic it's sending to the other LSR(s). Node N knows who the members of the MP2MP LSP are, so it advertises the member list to its directly connected members, excluding the member it's sending to. For example, node N advertises the list {LSR3,LSR1} to LSR2, leaving LSR2 out of it 🫶 Instead of advertising one PLR (like when N is not the root), a list of PLRs gets advertised using the procedures in Section 2.3.

Heads up bestie: the MP2MP root node protection mechanism does not replace the Root Node Redundancy (RNR) procedures in Section 7 of [RFC6388] 😭 The node protection procedures in this document help restore traffic for the existing MP2MP LSPs after a node failure, but a new root node still has to be elected eventually so new MP2MP LSPs can be created 🔥

Note, for the protected traffic to get exchanged between LSR1, LSR2, and LSR3, bidirectional LSPs have to exist between those LSRs, bypassing node N 🦋 How you set those LSPs up is outside the scope of this document, so that's a different story 🌈

2.3. PLR Information Encoding

okay the upstream LSR address gets conveyed via an LDP Notification message with an MP Status TLV 🎀 The MP Status TLV holds a brand new "PLR Status Value Element" that specifies the address of the PLR ✨

The new "PLR Status Value Element" is encoded like this 💖

 PLR Status Element:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Type =  2     |           Length              |  Addr Family  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Addr Fam cont | Num PLR entry |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   |                                                               |
   |                         PLR entry (1 or more)                 ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Where

      Type: PLR Status Value Element (Type 2).

      Length: The Length field is an unsigned integer that encodes the
      length of the Status Value following the Length field.  The
      encoded Length varies based on the Addr Family and the number of
      PLR entries.

      Addr Family: Two-octet quantity containing a value from IANA's
      "Address Family Numbers" registry [AFI] that encodes the address
      family for the PLR address encoded in the PLR entry.

      Num PLR entry: Element as an unsigned integer followed by the
      number of "PLR entry" fields in the format specified below.

The format of a "PLR Entry" looks like this 🧁

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |A|        Reserved             |       PLR address             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                  PLR address (cont)                           ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Where

      A bit: 0 = Withdraw, 1 = Add.

      Reserved: 15 bits; MUST be zero on transmit and ignored on
      receipt.

      PLR address: PLR address encoded according to the Address Family
      field encoded in the PLR Status Value Element.  Note that the
      length of the PLR address field is specific to the Address Family
      that is encoded.

The size of a "PLR Entry" is the 2 octets ("A bit + Reserved") plus the PLR address length 🌷 The PLR address length depends on the Address Family encoded in the PLR Status Value Element. A "PLR entry" is 6 octets for an IPv4 PLR address and 18 octets for an IPv6 PLR address 💜

If the PLR address on N changes for a given MP LSP, N needs to trigger a new PLR Status to update the MPT(s) 🔄 Node N can advertise or withdraw a given PLR from its PLR set by setting the A bit to 1 or 0 respectively in the matching PLR entry. Removing a PLR address is likely due to a link failure, so check out the procedures in Section 4.1 for that 💀 To remove all PLR addresses belonging to the encoded Address Family, an LSR N MUST encode a PLR Status Value Element with no PLR entry, and the "Num PLR entry" field MUST be set to zero 🙈

Both the PLR Status and an MP FEC TLV [RFC5036] MUST be included in the LDP Notification message, so a receiver can associate the PLR Status with the MP LSP 🫶

3. Using the tLDP Session 🦋

The receipt of a PLR MP Status (with PLR addresses) for an MP LSP on a receiving LSR makes it an MPT for node protection 👑 If it isn't already established, the MPT LSR MUST establish a tLDP session with all of the learned PLR addresses, using the procedures in [RFC7060] 🔥

Using Figure 1 as the reference topology, let's say both LSR2 and LSR3 are MPTs and have established a tLDP session with the PLR, which is LSR1 🌸 Assume both LSR2 and LSR3 have a FEC <R,X> with an upstream LSR N and label Ln assigned to the FEC towards N. The MPTs create a secondary upstream LSR for the FEC <R,X> (using the received PLR address) and assign label Lpx to it 💅 The MPTs do that for each PLR address learned for the MP LSP. In this example, the MPTs end up with a FEC <R,X> holding two local labels 🤯 Label Ln was assigned to N using the normal mLDP procedures, and Label Lpx was assigned to PLR (LSR1) for node protection. Note, when the protected node is an MP2MP root node, there is an upstream LSR for each PLR address that was advertised, each with a unique Label Lpx ✨

Receiving a FEC Label Mapping alone over the tLDP session from an MPT on a PLR conveys the label information, but it does not convey which node is being protected 😭 The MPT LSR knows that info and needs to tell the PLR too 🧚 For this reason, the FEC Label Mapping (FEC <R,X> : Lpx) that the MPT sends over the tLDP session to the PLR MUST include a Status TLV with an MP Status and a new LDP MP Status Value Element called the "Protected Node Status Value Element" 🎀 This new value element specifies the address of the node being protected. The "Protected Node Status Value Element" has the following format 🍓

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Type = 3      |           Length              | Addr  Family  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Addr Fam cont |        Node address                           ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Where

      Type : Protected Node Status Value Element (Type 3).

      Length: The Length field is an unsigned integer that encodes the
      length of the Status Value following the Length field.  The
      encoded Length varies based on the Address Family and is 6 octets
      for Address Family + IPv4 address and 18 octets for Address Family
      + IPv6 address.

      Addr Family: Two-octet quantity containing a value from IANA's
      "Address Family Numbers" registry [AFI] that encodes the address
      family for the node address.

      Node address: Protected node address encoded according to the
      Address Family field.

When a PLR receives a Label Mapping for FEC <R,X> that includes a Protected Node Status, it only uses that label binding once the Node advertised in the Status value becomes unreachable 🙈 If the LSP is an MP2MP LSP, the PLR would have assigned a Label Mapping for the upstream MP2MP FEC Element to the MPT ([RFC6388], Section 3) for FEC <R,X>. This label binding on the MPT MUST only be used once node N becomes unreachable 🔒

How to decide whether a node is unreachable is a local decision and it isn't spelled out in this document 🤷‍♀️ Typically, link failure or Bidirectional Forwarding Detection (BFD) can be used to determine and detect node unreachability 💫

4. Link or Node Failure 💥

Consider the following topology 🗺️

                           root
                            ^
                            |
                        . (LSR1)
                      .   / |  .
                     .  (M) |   .
                     .    \ |    .
                      .    (N)   .
                       .   /  \  .
                        . /    \.
                      (LSR2)  (LSR3)
                         |      |

               N: The node being protected.
               M: The backup node to protect link LSR1 - N.
               ...: Backup LSPs from LSR1 to LSR2 and LSR3.

                              Figure 3

Assume LSR1 is the PLR for protected node N, and LSR2 and LSR3 are MPTs for node N. When LSR1 discovers that node N is unreachable, it can't immediately tell whether the link from LSR1 to N failed or the actual node N did 🤔 In Figure 3, the link between LSR1 and N is also protected using Fast Reroute (FRR) [RFC4090] link protection via node M. LSR1 MAY simultaneously invoke both link protection via node M to N, using redirection of the traffic, and node protection directly to LSR1 and LSR2. If only the link failed, LSR2 and LSR3 get the packets twice because of the two protection mechanisms 😱 To stop duplicate packets from being forwarded to the receivers on the tree, LSR2 and LSR3 need to figure out which upstream node they should accept packets from. It can be either the primary upstream LSR N or the secondary upstream LSR1, but never both at the same time 🚫 The choice between the primary upstream LSR or (one or more) secondary upstream LSRs (on LSR2 and LSR3) is based on the reachability of the protected node N. As long as N is reachable from an MPT, the MPT should accept and forward the MPLS packets from N ✅ Once N becomes unreachable, the LSPs from the secondary upstream PLR LSRs (LSR1 in our example) get activated 🚀 Note that detecting whether N is unreachable is a local decision and isn't spelled out in this document 💜

Typically, link failure or BFD can be used to determine and detect node unreachability 🌈

4.1. Reconvergence after Node or Link Failure 🦋

okay so let's say we have this topology 👀✨

                           root
                            ^
                         _  |
                      /.  (LSR1)
                     /.   /. |  .\
                    /.  (M). |   .\
                  (P).    \. |    .\
                    \.     ( N )   .(Q)
                     \.   /     \   ./
                      \. /       \ ./
                     (LSR2)     (LSR3)
                        |          |

               N: The node being protected.
               M: The backup node to protect link 'LSR1 - N'.
               P and Q: The nodes on the new primary path after
                  failure of node N.
               ...: P2P backup LSPs.

Figure 4

so LSR1 has figured out that node N is unreachable 😭 and it's running BOTH the link protection and node protection procedures from this example. LSR1 is the PLR here 💅 and it's sending traffic over the backup P2P LSP to node N (via M) and also over the P2P LSPs straight to LSR2 and LSR3, who are acting as the MPT LSRs. Which path the events take depends on whether the link from LSR1 to N died or node N itself died. The downstream nodes that are protected and joining in on node protection MUST be able to tell that the protected node has become unreachable 🫶 Otherwise, none of the procedures below can be applied, sorry bestie 🙈

4.1.1. Node Failure 💀

if node N failed, LSR2 and LSR3 will both swap their primary upstream LSR over to the secondary one, which is LSR1, because node N is unreachable now 🥀 That means the label bindings that were previously given to LSR1 get activated on the MPTs (LSR2 and LSR3), and the label binding to N gets disabled. Traffic is now switched over to the label bindings that were set up for node protection. main character energy 👑

4.1.2. Link Failure 🔗

if the link 'LSR1 - N' failed instead, LSR2 and LSR3 won't change their primary upstream LSR, because node N is still reachable 🙌 They'll get traffic over two different bindings: the primary label binding for node N (from link protection via node M), and the binding for LSR1 from node protection. Since the secondary upstream LSRs haven't been activated yet, the traffic coming in through node protection gets dropped 🗑️ Node N will reconverge and tell LSR2 and LSR3 (see Section 2.3) that the PLR address (LSR1) isn't applicable anymore and has to be removed 😤 So LSR2 and LSR3 MUST send a Label Withdraw to LSR1 to withdraw the label binding. That stops the traffic from being forwarded over the backup P2P LSPs for node protection 🛑 LSR1 then responds with a Label Release as soon as the binding is gone ✨

4.1.3. Switching to New Primary Path 🛤️

the network will eventually reconverge, and LSR2 and LSR3 will each find a new best path to the root 🌈 LSR2 will find that P is its new primary upstream LSR to reach the root, and LSR3 will find Q. Honestly it doesn't matter whether the current active upstream LSR is node N or LSR1 (depending on the link or node failure) for the procedures below 🤷‍♀️ LSR2 and LSR3 SHOULD use the Make-Before-Break (MBB) procedures from Section 8 of [RFC6388] to switch over to the new primary upstream node. As soon as the new primary upstream LSRs P and Q are activated, a Label Withdraw message MUST be sent to the old upstream LSR 🦋 Also, switching upstream from a tLDP neighbor to a directly connected LDP neighbor is no different from switching between two directly connected neighbors, so no extra drama there 💖 Once LSR1 or node N gets the Label Withdraw message, forwarding stops and a Label Release is sent. bye bye old path 👋

When it's determined that there's no more interest in the tLDP session between the MPT and the PLR after reconvergence, the tLDP session MAY be taken down 🧚 It's possible that losing interest in the session is only temporary because of link flapping. To stop the tLDP session from flapping, it is RECOMMENDED to apply a delay before tearing it down ⏳ How long that delay is counts as a local implementation matter. If the operator isn't worried about the tLDP session flapping, and/or other procedures are already in place to avoid it entirely, then there's no need for the delay 🙅‍♀️

5. mLDP Capabilities for Node Protection 💖

in order to describe what the participating LSRs can do, this document organizes it by role in the network: Point of Local Repair (PLR), Merge Point (MPT), and protected node (as shown in Figure 1) 🎀

5.1. PLR Capability 🔥

a PLR node should handle the following conditions:

Accept an incoming tLDP session from the MPT LSR.
Support the receipt of a "Protected Node Status Value Element" status in an MP Status TLV over the tLDP session.
Upon node failure detection, be capable of switching traffic towards one or more MPT(s) over a P2P LSP (bypassing N), using the labels previously advertised for MP LSPs over the tLDP session.

an LSR that can do these things will advertise itself as PLR capable in the Node Protection Capability (see Section 5.4) ✨ This is a unidirectional capability, announced from the PLR to the protected LSR 📣

5.2. MPT Capability 🧜‍♀️

an MPT node should handle the following conditions;

Support the receipt of a "PLR Status Value Element" in an MP Status TLV from a protected node N.
Support transmitting a "Protected Node Status Value Element" in an MP Status TLV to a PLR.

an LSR that can do these things will advertise itself as MPT capable in the Node Protection Capability (see Section 5.4) 🌸 This is a unidirectional capability from the MPT to the protected LSR 💜

5.3. The Protected LSR 🛡️

a protected node should handle the following conditions:

Determine the PLR and MPT capability for directly connected upstream and downstream LSRs for a given MP FEC.
Support transmitting a "PLR Status Value Element" in an MP Status TLV to one or more downstream MPT LSRs.

the protected LSR doesn't advertise any capability for mLDP Node Protection, because it doesn't need to receive any of the MP Status values defined above 🤷‍♀️ It still plays a big role in the signaling and setup of node protection though 🫶 For a given FEC, the protected node can only send PLR information to a downstream LSR if the PLR has signaled the PLR capability and the downstream LSR has signaled the MPT capability. When the downstream LSR (acting as MPT) receives the PLR Status, it can implicitly infer that the advertised LSR(s) are PLR capable 🧠 At that point the MPT LSR can go ahead and set up a tLDP session with the PLR(s) and do the MP LSP node protection signaling 🚀

5.4. The Node Protection Capability 🎀

we define a single capability, "MP Node Protection Capability," to announce both the PLR and MPT capability 🙌

the format of the capability parameter TLV looks like this:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |U|F| Type = 0x0972             |           Length = 2          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |S| Reserved    |P|M| Reserved  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

and here's what each part means 👀

U/F bits: MUST be set to 1 and 0, respectively (as per [RFC5561]).
Type: MP Node Protection Capability (Type = 0x0972).
Length: Unsigned integer; MUST be set to 2.
S bit: Set to 1 to announce and 0 to withdraw the capability (as per [RFC5561]).
P bit: Set to 1 to indicate the PLR is capable of MP LSP node protection.
M bit: Set to 1 to indicate the MPT is capable of MP LSP node protection.
Reserved: MUST be zero on transmit and ignored on receipt.

the capability above can be sent in an LDP Initialization message to announce it at session establishment time 🌅 Or it can be sent in an LDP Capability message to dynamically update (announce or withdraw) it toward the peer, using the procedures in [RFC5561] 🔄

an LSR that supports the PLR functionality MAY send this capability to its downstream MP peers with the P bit set 🫧 An LSR that supports the MPT functionality MAY send this capability to its upstream peer with the M bit set 🌷 And an LSR that supports both the PLR and MPT functionality MAY send this capability to its peers with both the P and M bits set 🌈

6. Security Considerations 🔥

okay this part is SERIOUS 😤 The procedures in this document add two new TLVs to existing LDP messages. Those TLVs can be protected by the same mechanisms used to protect LDP messages, as described in [RFC6388] and [RFC5920] 🔐 If someone managed to attack the mechanisms in this document, an LSR (a PLR or an MPT) could be tricked into supporting a huge number of tLDP sessions and setting up an even bigger number of LSPs 😱 The security mechanisms in [RFC6388] and [RFC5920] are believed to be adequate. Still, an implementation could add extra protection by counting these protection sessions and LSPs, and writing a log message for the operator if a threshold gets crossed 🚨 stay safe bestie 🫶

7. IANA Considerations 🧚

IANA has allocated the following two new code points from the "LDP MP Status Value Element type" registry within the "Label Distribution Protocol (LDP) Parameters" registry 🎀

      Value | Name                                   | Reference
      ------+----------------------------------------+-----------
         2  | PLR Status Value Element               | this doc
      ------+----------------------------------------+-----------
         3  | Protected Node Status Value Element    | this doc

IANA has also assigned a new code point for a new Capability Parameter TLV 💖 The code point comes from the IETF Consensus range of the "TLV Type Name Space" registry within the "Label Distribution Protocol (LDP) Parameters" registry ✨

      Value | Description                   | Reference | Notes/Reg Date
      ------+-------------------------------+-----------+---------------
      0x0972| MP Node Protection Capability | this doc  |

8. References 📚

8.1. Normative References 📚

these are the docs you actually need to read to get this spec, so bookmark them bestie 🔖

[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>.

[RFC5036]  Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
           "LDP Specification", RFC 5036, DOI 10.17487/RFC5036,
           October 2007, <http://www.rfc-editor.org/info/rfc5036>.

[RFC6388]  Wijnands, IJ., Ed., Minei, I., Ed., Kompella, K., and B.
           Thomas, "Label Distribution Protocol Extensions for Point-
           to-Multipoint and Multipoint-to-Multipoint Label Switched
           Paths", RFC 6388, DOI 10.17487/RFC6388, November 2011,
           <http://www.rfc-editor.org/info/rfc6388>.

[RFC5561]  Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and JL.
           Le Roux, "LDP Capabilities", RFC 5561,
           DOI 10.17487/RFC5561, July 2009,
           <http://www.rfc-editor.org/info/rfc5561>.

[RFC7060]  Napierala, M., Rosen, E., and IJ. Wijnands, "Using LDP
           Multipoint Extensions on Targeted LDP Sessions", RFC 7060,
           DOI 10.17487/RFC7060, November 2013, <http://www.rfc-
           editor.org/info/rfc7060>.

[AFI]      IANA, "Address Family Numbers",
           <http://www.iana.org/assignments/address-family-numbers>.

8.2. Informative References 🧠

these are the extra reads for the deep-dive era, totally optional but so worth it 🌸

[RFC4090]  Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
           Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
           DOI 10.17487/RFC4090, May 2005,
           <http://www.rfc-editor.org/info/rfc4090>.

[RFC5286]  Atlas, A., Ed., and A. Zinin, Ed., "Basic Specification
           for IP Fast Reroute: Loop-Free Alternates", RFC 5286,
           DOI 10.17487/RFC5286, September 2008,
           <http://www.rfc-editor.org/info/rfc5286>.

[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>.

[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>.

Acknowledgments 🫶

okay the authors have to shout out their besties, so here we go ✨ the authors thank Nagendra Kumar, Duan Hong, Martin Vigoureux, Kenji Fujihira, Loa Andersson, and Ben Campbell for their comments on this document 💖 and many thanks also go to Elwyn Davies and Adrian Farrel for the detailed review and contribution to this document 👑

Contributors 🎀

the following individual contributed to this document 💜

Eric Rosen
Juniper Networks, Inc.
10 Technology Park Drive
Westford, MA  01886
United States
Email: erosen@juniper.net

Authors' Addresses 🦋

and here are the people who wrote this whole thing, with where to find them 🌈

IJsbrand Wijnands (editor)
Cisco Systems, Inc.
De kleetlaan 6a
Diegem  1831
Belgium

Email: ice@cisco.com


Kamran Raza
Cisco Systems, Inc.
2000 Innovation Drive
Ottawa, Ontario K2K-3E8
Canada

Email: skraza@cisco.com


Alia Atlas
Juniper Networks, Inc.
10 Technology Park Drive
Westford, MA  01886
United States

Email: akatlas@juniper.net


Jeff Tantsura
Ericsson
300 Holger Way
San Jose, CA  95134
United States

Email: jeff.tantsura@ericsson.com


Quintin Zhao
Huawei Technology
125 Nagog Technology Park
Acton, MA  01719
United States

Email: quintin.zhao@huawei.com

📦 where this page comes from

ietf: rfc7715 2016-01
💖 girlified by claude-haiku-5-5 on 2026-10-18: a language model's rewrite of the original, under its terms

RFC 7715

📜 RFC 7715: Multipoint LDP (mLDP) Node Protection 🎀

Abstract

Status of This Memo

Copyright Notice

Table of Contents

1. Introduction ✨

1.1. Conventions Used in This Document 🌈

1.2. Terminology 📚

2. PLR Determination 🦋

2.1. Transit Node Procedure 🧚

2.2. MP2MP Root Node Procedure

2.3. PLR Information Encoding

3. Using the tLDP Session 🦋

4. Link or Node Failure 💥

4.1. Reconvergence after Node or Link Failure 🦋

4.1.1. Node Failure 💀

4.1.2. Link Failure 🔗

4.1.3. Switching to New Primary Path 🛤️

5. mLDP Capabilities for Node Protection 💖

5.1. PLR Capability 🔥

5.2. MPT Capability 🧜‍♀️

5.3. The Protected LSR 🛡️

5.4. The Node Protection Capability 🎀

6. Security Considerations 🔥

7. IANA Considerations 🧚

8. References 📚

8.1. Normative References 📚

8.2. Informative References 🧠

Acknowledgments 🫶

Contributors 🎀

Authors' Addresses 🦋