--- title: IPv6 Unique Local Addresses (ULA) Made Useless «... description: RFC 6724's address selection rules cause IPv6 Unique Local Addresses (ULA) to be ranked lower than IPv4 addresses in dual-stack networks, effectively making... canonical: https://daily.dev/posts/ipv6-unique-local-addresses-ula-made-useless-ipspace-net-blog-c5yn7mftk twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: IPv6 Unique Local Addresses (ULA) Made Useless « ipSpace.net blog | daily.dev og:description: RFC 6724's address selection rules cause IPv6 Unique Local Addresses (ULA) to be ranked lower than IPv4 addresses in dual-stack networks, effectively making... og:url: https://daily.dev/posts/ipv6-unique-local-addresses-ula-made-useless-ipspace-net-blog-c5yn7mftk og:image: https://api.daily.dev/og/posts/C5YN7MFtk.png og:image:alt: IPv6 Unique Local Addresses (ULA) Made Useless « 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. # IPv6 Unique Local Addresses (ULA) Made Useless « ipSpace.net blog **[ipSpace.net Blog](https://daily.dev/sources/ipspace)** · 2 min read · 0 upvotes · 0 comments ## Summary RFC 6724's address selection rules cause IPv6 Unique Local Addresses (ULA) to be ranked lower than IPv4 addresses in dual-stack networks, effectively making IPv6 unused when only ULA addresses are deployed. An IETF draft by Nick Buraglio, Chris Cummings, and Russ White documents these unintended operational issues. Using ULA alongside Global Unicast Addresses (GUA) as a fallback also introduces hidden problems that only surface when IPv4 is disabled. The post references a valid ULA use case — site-to-site VPN with local Internet exit — and links to related blog posts and IETF discussions. Community comments confirm the behavior across Linux, Windows, Android, and iOS, with most OS network stacks hard-coded to prefer IPv4 over ULA. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### Why is IPv6 ULA traffic not being used in my dual-stack network even though ULA addresses are configured? RFC 6724's address selection rules rank IPv6 Unique Local Addresses (ULA) lower than IPv4 addresses, so in a dual-stack network, the OS will prefer IPv4 over ULA-addressed IPv6. This is not a misconfiguration — it is the common interpretation of RFC 6724 baked into network stacks on Linux, Windows, Android, and iOS. The only workaround is to use Global Unicast Addresses (GUA) instead of ULA. _Engineers troubleshooting IPv6 adoption in dual-stack environments track issues like this on daily.dev._ ### Is there any valid use case for IPv6 ULA addresses in enterprise networks? One documented use case is site-to-site VPN with local Internet exit in mid-sized enterprise networks. ULA addresses provide stable internal addressing that does not depend on a provider-assigned prefix, which is useful when each site exits to the Internet locally and GUA prefixes may change. However, this use case is undermined if the network is dual-stack, since ULA will be deprioritized over IPv4. _Networking teams evaluating IPv6 address planning strategies find relevant discussions on daily.dev._ ## Similar posts on daily.dev - [UDP Broadcasting And The Brave New World Of IPv6](https://daily.dev/posts/udp-broadcasting-and-the-brave-new-world-of-ipv6-kbr2qsudb) · Hackaday · 0 upvotes · 0 comments - [I spent a WEEK without IPv4 to understand IPv6 transition mechanisms](https://daily.dev/posts/i-spent-a-week-without-ipv4-to-understand-ipv6-transition-mechanisms-iscykz0il) · Hacker News · 2 upvotes · 0 comments - [IPv6 in 2025 – Transitioning to IPv6](https://daily.dev/posts/ipv6-in-2025-transitioning-to-ipv6-x1lwgorkb) · Cisco · 0 upvotes · 0 comments - [IPv6 zones in URLs are a mistake](https://daily.dev/posts/ipv6-zones-in-urls-are-a-mistake-kqhqi4phq) · Lobsters · 0 upvotes · 0 comments --- Tags: [#networking](https://daily.dev/tags/networking) [View this post on daily.dev](https://daily.dev/posts/ipv6-unique-local-addresses-ula-made-useless-ipspace-net-blog-c5yn7mftk) ```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":"IPv6 Unique Local Addresses (ULA) Made Useless « ipSpace.net blog","url":"https://daily.dev/posts/ipv6-unique-local-addresses-ula-made-useless-ipspace-net-blog-c5yn7mftk","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/ipv6-unique-local-addresses-ula-made-useless-ipspace-net-blog-c5yn7mftk"},"datePublished":"2026-08-11T08:53:33.496Z","dateModified":"2026-08-11T09:10:36.615Z","description":"RFC 6724's address selection rules cause IPv6 Unique Local Addresses (ULA) to be ranked lower than IPv4 addresses in dual-stack networks, effectively making...","image":"https://media.daily.dev/image/upload/s--OHB84bZF--/f_auto/v1722860399/public/Placeholder%2010","thumbnailUrl":"https://media.daily.dev/image/upload/s--OHB84bZF--/f_auto/v1722860399/public/Placeholder%2010","isAccessibleForFree":true,"articleSection":"ipSpace.net Blog","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"ipSpace.net Blog","logo":"https://media.daily.dev/image/upload/s--xS7E82MT--/f_auto,q_auto/v1786438303/logos/ipspace?_a=BAMAMicg0","url":"https://daily.dev/sources/ipspace"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/ipv6-unique-local-addresses-ula-made-useless-ipspace-net-blog-c5yn7mftk","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"networking","timeRequired":"PT2M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"ipSpace.net Blog","item":"https://daily.dev/sources/ipspace"},{"@type":"ListItem","position":3,"name":"IPv6 Unique Local Addresses (ULA) Made Useless « ipSpace.net blog"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/ipv6-unique-local-addresses-ula-made-useless-ipspace-net-blog-c5yn7mftk#faq","mainEntity":[{"@type":"Question","name":"Why is IPv6 ULA traffic not being used in my dual-stack network even though ULA addresses are configured?","acceptedAnswer":{"@type":"Answer","text":"RFC 6724's address selection rules rank IPv6 Unique Local Addresses (ULA) lower than IPv4 addresses, so in a dual-stack network, the OS will prefer IPv4 over ULA-addressed IPv6. 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