--- title: The Never-Ending IPv6 Loopback Prefix Saga « ipSpace.net... description: Different networking vendors handle the OSPFv3 rule that loopback prefixes must be advertised as /128s inconsistently. Arista EOS ignores the RFC and... canonical: https://daily.dev/posts/the-never-ending-ipv6-loopback-prefix-saga-ipspace-net-blog-4nlhgh10l twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: The Never-Ending IPv6 Loopback Prefix Saga « ipSpace.net blog | daily.dev og:description: Different networking vendors handle the OSPFv3 rule that loopback prefixes must be advertised as /128s inconsistently. Arista EOS ignores the RFC and... og:url: https://daily.dev/posts/the-never-ending-ipv6-loopback-prefix-saga-ipspace-net-blog-4nlhgh10l og:image: https://api.daily.dev/og/posts/4NlHGh10L.png og:image:alt: The Never-Ending IPv6 Loopback Prefix Saga « 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. # The Never-Ending IPv6 Loopback Prefix Saga « ipSpace.net blog **[ipSpace.net Blog](https://daily.dev/sources/ipspace)** · 3 min read · 0 upvotes · 0 comments ## Summary Different networking vendors handle the OSPFv3 rule that loopback prefixes must be advertised as /128s inconsistently. Arista EOS ignores the RFC and advertises the configured prefix, Nokia SR OS forces /128 only, FRRouting now advertises both, BIRD lets you configure anything, and Cisco IOS offers a workaround knob. With loopbacks now used as VXLAN endpoints requiring fast lookups, this inconsistency creates real hardware and interoperability headaches, and the suggested workaround is switching to IS-IS or BGP as the IPv6 IGP instead of OSPFv3. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### Does the OSPFv3 RFC require loopback prefixes to always be advertised as /128 regardless of interface configuration? Yes, RFC 5340 section 4.4.3.9 states that loopback prefixes must always be advertised as /128 in OSPFv3, regardless of what prefix length is configured on the interface. This matters because datacenter switches now use loopbacks as VXLAN endpoints, where high-speed forwarding to longer prefixes can strain TCAM hardware resources. _daily.dev surfaces networking deep dives like this for engineers debugging IPv6 loopback and VXLAN routing quirks._ ### Which network OS vendors do not follow the OSPFv3 /128 loopback advertisement rule? Arista EOS ignores the RFC 5340 requirement and advertises loopback prefixes as configured rather than forcing /128. Nokia SR OS takes the opposite extreme, refusing anything but a /128 on the system loopback. FRRouting previously behaved like Arista but now advertises both the configured prefix and the /128, while Cisco IOS offers a workaround command (ipv6 ospf network point-to-point) to override the RFC behavior. _Engineers comparing router OS behavior can track vendor quirks like these on daily.dev before choosing an IGP._ ### What is the recommended alternative to OSPFv3 for IPv6 routing given the loopback prefix inconsistencies across vendors? Using IS-IS or BGP as the IPv6 interior gateway protocol avoids the inconsistent /128 loopback advertisement behavior seen across OSPFv3 implementations from vendors like Arista EOS, Nokia SR OS, FRRouting, BIRD, and Cisco IOS. This sidesteps the mess of vendor-specific workarounds needed to keep loopback prefixes usable as VXLAN endpoints with efficient hardware lookups. _daily.dev helps network engineers weigh IGP choices like IS-IS versus OSPFv3 for IPv6 datacenter fabrics._ ## Similar posts on daily.dev - [BGP-Free Network Core with SRv6 « ipSpace.net blog](https://daily.dev/posts/bgp-free-network-core-with-srv6-ipspace-net-blog-9bbn88wub) · ipSpace.net Blog · 0 upvotes · 0 comments - [The OSPF MTU Mismatch Saga « ipSpace.net blog](https://daily.dev/posts/the-ospf-mtu-mismatch-saga-ipspace-net-blog-jmtvuzjm6) · ipSpace.net Blog · 0 upvotes · 0 comments - [Sample netlab SRv6 Lab Topologies « ipSpace.net blog](https://daily.dev/posts/sample-netlab-srv6-lab-topologies-ipspace-net-blog-s8nppf7yo) · 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 --- [View this post on daily.dev](https://daily.dev/posts/the-never-ending-ipv6-loopback-prefix-saga-ipspace-net-blog-4nlhgh10l) ```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":"The Never-Ending IPv6 Loopback Prefix Saga « ipSpace.net blog","url":"https://daily.dev/posts/the-never-ending-ipv6-loopback-prefix-saga-ipspace-net-blog-4nlhgh10l","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/the-never-ending-ipv6-loopback-prefix-saga-ipspace-net-blog-4nlhgh10l"},"datePublished":"2026-08-17T06:11:37.652Z","dateModified":"2026-08-17T06:12:00.738Z","description":"Different networking vendors handle the OSPFv3 rule that loopback prefixes must be advertised as /128s inconsistently. 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