--- title: LDP Creation Myths « ipSpace.net blog | daily.dev description: A historical deep-dive into why MPLS ended up with LDP rather than a simpler label distribution mechanism. The core reason: MPLS was originally designed to... canonical: https://daily.dev/posts/ldp-creation-myths-ipspace-net-blog-o7tfqbrby twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: LDP Creation Myths « ipSpace.net blog | daily.dev og:description: A historical deep-dive into why MPLS ended up with LDP rather than a simpler label distribution mechanism. The core reason: MPLS was originally designed to... og:url: https://daily.dev/posts/ldp-creation-myths-ipspace-net-blog-o7tfqbrby og:image: https://api.daily.dev/og/posts/O7TfQBRbY.png og:image:alt: LDP Creation Myths « ipSpace.net blog og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # LDP Creation Myths « ipSpace.net blog **[ipSpace.net Blog](https://daily.dev/sources/ipspace)** · 4 min read · 0 upvotes · 0 comments ## Summary A historical deep-dive into why MPLS ended up with LDP rather than a simpler label distribution mechanism. The core reason: MPLS was originally designed to integrate ATM switches (Fore Systems) with IP routers, competing with Ipsilon's proprietary technology. ATM hardware constraints — limited label space, per-interface label allocation, and inability to process IP packets at speed — forced downstream-on-demand label allocation and independent label control was impossible. The MPLS design team was also organizationally separated from IGP teams and instructed not to touch IGP code, which prevented the simpler SR-like approach. A first SR prototype in 2014 needed only ~500 lines added to IS-IS to achieve full any-to-any connectivity, highlighting how much complexity LDP added unnecessarily. The post also notes that SR-MPLS works best with a single link-state IGP, and that route redistribution across multiple protocols would undermine it. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### Why does MPLS use LDP instead of distributing labels directly via IGPs like IS-IS? MPLS was originally designed to integrate ATM switches with IP routers, competing with Fore Systems and Ipsilon. ATM hardware had limited label space, required per-interface label allocation, and could not process IP packets at speed — making downstream-on-demand label allocation the only viable option. Additionally, the MPLS design team was organizationally separated from IGP teams and told not to touch IGP code, ruling out an IS-IS-integrated approach. _Network engineers untangling MPLS design decisions find the historical context on daily.dev._ ### How many lines of code did the first MPLS Segment Routing prototype add to IS-IS? The first MPLS-SR node label prototype required only about 500 lines of code added to a vanilla IPv4/IPv6 IS-IS codebase. That incremental change delivered full any-to-any connectivity with no synchronization issues and no need for targeted sessions for Remote LFA — essentially providing labeled transport for free, in stark contrast to the complexity LDP introduced. _Engineers evaluating segment routing vs LDP trade-offs keep up with networking discussions on daily.dev._ ## Similar posts on daily.dev - [MPLS/VPN with SR-MPLS Core « ipSpace.net blog](https://daily.dev/posts/mpls-vpn-with-sr-mpls-core-ipspace-net-blog-nw3uwiphe) · ipSpace.net Blog · 0 upvotes · 0 comments - [BGP-Free Core with SR-MPLS « ipSpace.net blog](https://daily.dev/posts/bgp-free-core-with-sr-mpls-ipspace-net-blog-h7kronzy3) · ipSpace.net Blog · 0 upvotes · 0 comments - [Multivendor SR-MPLS « ipSpace.net blog](https://daily.dev/posts/multivendor-sr-mpls-ipspace-net-blog-qekokwduk) · ipSpace.net Blog · 0 upvotes · 0 comments --- Tags: [#networking](https://daily.dev/tags/networking), [#bgp](https://daily.dev/tags/bgp) [View this post on daily.dev](https://daily.dev/posts/ldp-creation-myths-ipspace-net-blog-o7tfqbrby) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"LDP Creation Myths « ipSpace.net blog","url":"https://daily.dev/posts/ldp-creation-myths-ipspace-net-blog-o7tfqbrby","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/ldp-creation-myths-ipspace-net-blog-o7tfqbrby"},"datePublished":"2026-08-11T08:52:12.189Z","dateModified":"2026-08-11T09:00:32.469Z","description":"A historical deep-dive into why MPLS ended up with LDP rather than a simpler label distribution mechanism. 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ATM hardware had limited label space, required per-interface label allocation, and could not process IP packets at speed — making downstream-on-demand label allocation the only viable option. Additionally, the MPLS design team was organizationally separated from IGP teams and told not to touch IGP code, ruling out an IS-IS-integrated approach. Network engineers untangling MPLS design decisions find the historical context on daily.dev."}},{"@type":"Question","name":"How many lines of code did the first MPLS Segment Routing prototype add to IS-IS?","acceptedAnswer":{"@type":"Answer","text":"The first MPLS-SR node label prototype required only about 500 lines of code added to a vanilla IPv4/IPv6 IS-IS codebase. That incremental change delivered full any-to-any connectivity with no synchronization issues and no need for targeted sessions for Remote LFA — essentially providing labeled transport for free, in stark contrast to the complexity LDP introduced. Engineers evaluating segment routing vs LDP trade-offs keep up with networking discussions on daily.dev."}}]} ```