RFC 5037

Experience with the Label Distribution Protocol (LDP) 💖

Network Working Group 🎀 Request for Comments: 5037 🦋 Category: Informational ✨ Date: October 2007 🌸

Authors (all editors):

• Loa Andersson, Ed. (Acreo AB) 🧚
• Ina Minei, Ed. (Juniper Networks) 💜
• Bob Thomas, Ed. (Cisco Systems, Inc.) 🍓

Obsoletes / Updates: none listed in the title block. 🙈

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Status of This Memo ✨

okay so this memo is just informational 💅 It gives info to the Internet community, and it does not specify an Internet standard of any kind. Distribution is unlimited, so share the tea 🫶

Abstract 🌈

so the whole point of this memo is to show how LDP (Label Distribution Protocol) checks off some of the requirements from RFC 1264 for working group protocols in the IETF Routing Area to move up to Draft Standard ✨ Specifically, it's about operational experience with LDP, which is requirement 5 of section 5.0 in RFC 1264. 🔥

Table of Contents 📑

1. Introduction ....................................................2
2. Operational Experience ..........................................2
   2.1. Environment and Duration ...................................2
   2.2. Applications and Motivation ................................3
   2.3. Protocol Features ..........................................3
   2.4. Security Concerns ..........................................4
   2.5. Implementations and Inter-Operability ......................4
   2.6. Operational Experience .....................................4
3. Security Considerations .........................................5
4. Acknowledgments .................................................5
5. References ......................................................6
   5.1. Normative References .......................................6
   5.2. Informative References .....................................6

1. Introduction 🦋

so, same energy as the abstract: this memo documents how some of the requirements in [RFC1264] for advancing protocols developed by working groups within the IETF Routing Area to Draft Standard have been satisfied by LDP. Specifically, it's the operational experience with LDP, requirement 5 of section 5.0 in RFC 1264. 💅

LDP was first published as [RFC3036] in January 2001 🌸 It came out of the MPLS Working Group of the IETF and was co-authored by Loa Andersson, Paul Doolan, Nancy Feldman, Andre Fredette, and Bob Thomas. It has since been obsoleted by [RFC5036]. 👑

2. Operational Experience ✨

this section is the juicy part 🍓 It talks about operational experience with the protocol, and the info comes from a survey sent to the MPLS Working Group in October 2004. You can find the questionnaire in the MPLS Working Group mail archives for October 2004. 📬

11 responses came in, and all but 2 asked for confidentiality, so the results are summarized to keep things private 🙈 The networks surveyed were in different geographic locations: US, Europe, and Asia 🌍 Both academic and commercial networks responded. literally a whole mix 🔥

2.1. Environment and Duration 🌸

the size of the deployments goes from less than 20 Label Switching Routers (LSRs) all the way up to over 1000 LSRs 😭 Eight out of the 11 deployments use LDP in both the edge and the core, two use it on the edge only, and one uses it in the core only.

sessions exist to peers found through both the basic and the extended discovery mechanisms 🧚 In half the cases, more than one adjacency (and as many as four adjacencies) is maintained per session. The average number of LDP sessions on an LSR ranges from under 10 to just over 80. The responses break down like this: under 10: 4 responses, 20-50: 4 responses, and over 80: 1 response. 📊

in the surveyed networks, LDP has been deployed anywhere from under 1 year to over 4 years. The responses break down like this: under 1 year: 3 responses, 2 years: 2 responses, 3 years: 3 responses, and over 4 years: 3 responses. ⭐

2.2. Applications and Motivation 💜

nine of the 11 responses say Layer 3 Virtual Private Networks (L3VPNs) are the application driving the LDP deployment in their network 👑

the full list of applications goes like this: L3VPNs: 9, pseudowires: 4 current (and one planned deployment), L2VPNs: 4, forwarding based on labels: 2, and BGP-free core: 1. 🫶

there are two major options for label distribution protocols: LDP and Resource Reservation Protocol-Traffic Engineering (RSVP-TE). One of the big differences is that RSVP-TE supports traffic engineering, while LDP does not. ngl that's the main fork in the road 🛣️ The reasons people gave for picking LDP as the label distribution protocol are:

• The deployment does not require traffic engineering - 6
• Inter-operability concerns if a different protocol is used - 5
• Equipment vendor only supports LDP - 5
• Ease of configuration - 4
• Ease of management - 3
• Scalability concerns with other protocols - 3
• Required for a service offering of the service provider - 1

2.3. Protocol Features 🧚

all of the deployments surveyed use the Downstream Unsolicited Label Distribution mode 🌈 All but one deployment use Liberal Label retention, and that one uses conservative. 💅

LSP setup is established with both independent and Ordered Control. Five of the deployments use both control modes in the same network. ✨

the number of LDP Forwarding Equivalence Classes (FECs) advertised and LDP routes installed falls into one of two categories: 1) roughly the same as the number of LSRs in the network, and 2) roughly the same as the number of IGP routes in the network. Of the 8 responses received, 6 were in the first category and 2 were in the second. 🎀

2.4. Security Concerns 🙈

one of the operators raised a security concern: there's no mechanism for securing LDP Hellos. 💀

2.5. Implementations and Inter-Operability 🦋

eight of the 11 responses say more than one implementation (and as many as four different ones) is deployed in the same network 🔥

the consensus is that even though implementations differ, no inter-operability issues exist 🫶 The challenges listed by providers running multiple implementations are:

• Different flexibility in picking for which FECs to advertise labels.
• Different flexibility in setting transport and LDP router-id addresses.
• Different default utilization of LDP labels for traffic resolution. Some vendors use LDP for both VPN and IPv4 traffic forwarding, while other vendors allow only VPN traffic to resolve via LDP. The challenge is to restrict the utilization of LDP labels to VPN traffic in a mixed-vendor environment. 😤
• Understanding the differences in the implementations. 🤔

2.6. Operational Experience 🌸

in general, operators reported stable implementations and steady improvement in resiliency to failure and convergence times over the years 📈 Some operators said they haven't found any issues with the protocol since deploying it. 🥹

the operational issues reported fall into three categories:

1. Configuration issues. Both the session and adjacency endpoints must be allowed by the firewall filters. Misconfiguring the filters causes sessions to drop (if already established) or fail to establish. 🧱
2. Vendor bugs. These include traffic blackholing, unnecessary label withdrawals and changes, session resets, and problems migrating from older versions of the technology. Most reports said the problems happened in early versions of the implementations. 🐛
3. Protocol issues.
   • The synchronization required between LDP and the IGP was listed as the main protocol issue. Two issues were reported: 1) slow convergence, because LDP convergence time is tied to the IGP convergence time, and 2) traffic blackholing on a link-up event. When an interface comes up, the LDP session may come up slower than the IGP session. This results in dropping MPLS traffic for a link-up event (not a failure but a restoration). This issue is described in more detail in [LDP-SYNC]. 🌊
   • Silent failures. Failure not being propagated to the head end of the LSP when setting up LSPs using independent control. 🫥

Intellectual Property ✨

okay so bestie, this part is all about who owns what 💅 The IETF takes no position on whether any Intellectual Property Rights or other rights that someone might claim over the technology in this document are valid or how far they reach 🙈 It also doesn't say whether any license under those rights might or might not be available, and it hasn't made any independent effort to find out whether such rights exist. Total neutrality, no cap 💖

The place to learn the procedures for rights in RFC documents is BCP 78 and BCP 79 📚 Those are the rulebooks, iykyk 🌸

Copies of IPR disclosures sent to the IETF Secretariat are a whole thing 🦋 So are any assurances of licenses that are going to be available, plus the results of any attempt to get a general license or permission for implementers or users of this specification to use those proprietary rights. All of that lives in the IETF on-line IPR repository at http://www.ietf.org/ipr 🔥

And the IETF is literally inviting anyone who's interested to speak up ✨ If you know about any copyrights, patents, patent applications, or other proprietary rights that might cover technology needed to implement this standard, send it over to the IETF at ietf-ipr@ietf.org 🫶 Main character energy for transparency, periodt 👑