--- title: Scalability Aspects of SR-MPLS « ipSpace.net blog description: A deep-dive discussion on the scalability challenges of SR-MPLS in large networks, sparked by a community comment from Henk Smit. Key topics include IS-IS area... canonical: https://daily.dev/posts/scalability-aspects-of-sr-mpls-ipspace-net-blog-oyh9nafch twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Scalability Aspects of SR-MPLS « ipSpace.net blog | daily.dev og:description: A deep-dive discussion on the scalability challenges of SR-MPLS in large networks, sparked by a community comment from Henk Smit. Key topics include IS-IS area... og:url: https://daily.dev/posts/scalability-aspects-of-sr-mpls-ipspace-net-blog-oyh9nafch og:image: https://api.daily.dev/og/posts/OYH9NAfCh.png og:image:alt: Scalability Aspects of SR-MPLS « 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. # Scalability Aspects of SR-MPLS « ipSpace.net blog **[ipSpace.net Blog](https://daily.dev/sources/ipspace)** · 9 min read · 0 upvotes · 0 comments ## Summary A deep-dive discussion on the scalability challenges of SR-MPLS in large networks, sparked by a community comment from Henk Smit. Key topics include IS-IS area sizing limits (practical ceiling around 1k-3k routers in a flat L2 area, with things getting difficult above 5k), the challenge of advertising per-router SIDs (/32 or /128) without summarization, LSPDB growth with flex-algo, and the trade-offs between SR-MPLS and SRv6 (which supports summarizable SIDs but introduces path liveliness issues). Solutions discussed include BGP-LU (RFC 8669) for distributing SR SIDs across areas, SDN controllers for multi-area topology and alternate path calculation, and the emerging IS-IS flood reflection draft. Expert commentary from Jeff Tantsura and Tony Przygienda adds real-world implementation nuance, including vendor differences, tuning complexity, and the non-linear cost of distributed synchronized state at scale. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### How many routers can fit in a single IS-IS area when running SR-MPLS? In a well-tuned IS-IS flat L2 network with dual-stack and SR, you can scale to roughly 3,000 routers while keeping SPF times low and topology stable. Pushing above 5,000 routers is where things get difficult. The traditional soft limit of around 1,000 routers per area is considered outdated by practitioners with large-scale deployment experience. _Engineers scaling SR-MPLS deployments track implementation limits like these on daily.dev._ ### How do you distribute SR-MPLS SIDs across IS-IS areas without advertising every /32 loopback into the backbone? BGP-LU (RFC 8669) can distribute SR SIDs across area boundaries, avoiding the need to flood every router loopback and its SID through IS-IS inter-area leakage. Alternatively, an SDN controller can collect multi-area topology and install computed paths. IS-IS flood reflection (draft-ietf-lsr-isis-flood-reflection) is another emerging approach that extends flat IS-IS to arbitrary scale without L1/L2 topology restrictions while supporting TE and SR. _Architects choosing between BGP-LU and SDN controllers for SR-MPLS multi-area designs find the trade-off discussions on daily.dev._ ### Does SRv6 have better scalability than SR-MPLS for large networks? SRv6 supports summarizable SIDs, which SR-MPLS lacks, giving it an advantage in reducing the amount of per-router state that must be advertised. However, SRv6 is fundamentally a tunneling protocol (comparable to VXLAN, GENEVE, or LISP), and tunneling protocols that send payload toward a summarized underlay prefix face a path liveliness problem. You still need the /32-to-SID mapping even with summarizable SIDs. _Deciding between SR-MPLS and SRv6 for a large-scale rollout? The ongoing debate surfaces regularly 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: [#bgp](https://daily.dev/tags/bgp) [View this post on daily.dev](https://daily.dev/posts/scalability-aspects-of-sr-mpls-ipspace-net-blog-oyh9nafch) ```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":"Scalability Aspects of SR-MPLS « ipSpace.net blog","url":"https://daily.dev/posts/scalability-aspects-of-sr-mpls-ipspace-net-blog-oyh9nafch","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/scalability-aspects-of-sr-mpls-ipspace-net-blog-oyh9nafch"},"datePublished":"2026-08-11T08:54:51.951Z","dateModified":"2026-08-11T09:35:17.002Z","description":"A deep-dive discussion on the scalability challenges of SR-MPLS in large networks, sparked by a community comment from Henk Smit. 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