--- title: IPv6 and the Revenge of the Stupid Bridges « ipSpace.net... description: During VRRPv3 IPv6 integration testing with netlab, Aruba CX, Cumulus Linux with NVUE, and Dell OS10 consistently failed tests. The root cause was discovered... canonical: https://daily.dev/posts/ipv6-and-the-revenge-of-the-stupid-bridges-ipspace-net-blog-uxahu24sy twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: IPv6 and the Revenge of the Stupid Bridges « ipSpace.net blog | daily.dev og:description: During VRRPv3 IPv6 integration testing with netlab, Aruba CX, Cumulus Linux with NVUE, and Dell OS10 consistently failed tests. The root cause was discovered... og:url: https://daily.dev/posts/ipv6-and-the-revenge-of-the-stupid-bridges-ipspace-net-blog-uxahu24sy og:image: https://api.daily.dev/og/posts/UXahU24sy.png og:image:alt: IPv6 and the Revenge of the Stupid Bridges « 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 and the Revenge of the Stupid Bridges « ipSpace.net blog **[ipSpace.net Blog](https://daily.dev/sources/ipspace)** · 4 min read · 0 upvotes · 0 comments ## Summary During VRRPv3 IPv6 integration testing with netlab, Aruba CX, Cumulus Linux with NVUE, and Dell OS10 consistently failed tests. The root cause was discovered by Jeroen van Bemmel: Arista cEOS containers, when deployed with minimal startup configuration, place all interfaces into VLAN 1 as a bridge, causing IPv6 router advertisements to be forwarded between separate LAN segments. This made Linux hosts believe both IPv6 prefixes were directly connected, bypassing first-hop routers entirely. The failure was timing-dependent — it only affected devices configured before the EOS switch finished its own configuration. The fix in netlab 1.9.4 adds a normalization step that shuts down data-plane interfaces on Arista EOS and Cisco IOS L2 devices before initial configuration. The post also revisits the broader concern that switches booting without configuration may act as transparent bridges, bridging VLANs that should be isolated. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### Why does my Arista cEOS container forward IPv6 router advertisements between separate LAN segments? Arista cEOS containers deployed with minimal or no startup configuration place all interfaces into VLAN 1 in bridge mode by default. This causes the container to act as a transparent bridge, forwarding IPv6 router advertisements between connected LAN segments. The fix is to either add 'switchport default mode routed' to the startup config, or shut down data-plane interfaces before applying configuration, as netlab 1.9.4 does. _Engineers running network labs with cEOS track issues like this on daily.dev before they waste hours debugging._ ### What was the fix for Arista EOS and Cisco IOS L2 devices acting as bridges before configuration in netlab? Netlab 1.9.4 introduced a normalization configuration step that runs before initial interface configuration. This step shuts down data-plane interfaces on Arista EOS and Cisco IOS L2 devices, preventing them from bridging traffic between segments during the configuration window. An alternative for Arista is to set 'switchport default mode routed' in the startup config, though this allocates internal VLANs per port. _Developers automating network lab deployments find netlab release notes and workarounds like this on daily.dev._ ## Similar posts on daily.dev - [The Never-Ending IPv6 Loopback Prefix Saga « ipSpace.net blog](https://daily.dev/posts/the-never-ending-ipv6-loopback-prefix-saga-ipspace-net-blog-4nlhgh10l) · ipSpace.net Blog · 0 upvotes · 0 comments - [Arista cEOS Does Not Apply ACLs to Control-Plane Traffic « ipSpace.net blog](https://daily.dev/posts/arista-ceos-does-not-apply-acls-to-control-plane-traffic-ipspace-net-blog-ieh2uzhm7) · ipSpace.net Blog · 0 upvotes · 0 comments --- Tags: [#networking](https://daily.dev/tags/networking) [View this post on daily.dev](https://daily.dev/posts/ipv6-and-the-revenge-of-the-stupid-bridges-ipspace-net-blog-uxahu24sy) ```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 and the Revenge of the Stupid Bridges « ipSpace.net blog","url":"https://daily.dev/posts/ipv6-and-the-revenge-of-the-stupid-bridges-ipspace-net-blog-uxahu24sy","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/ipv6-and-the-revenge-of-the-stupid-bridges-ipspace-net-blog-uxahu24sy"},"datePublished":"2026-08-11T08:53:29.944Z","dateModified":"2026-08-24T06:53:23.508Z","description":"During VRRPv3 IPv6 integration testing with netlab, Aruba CX, Cumulus Linux with NVUE, and Dell OS10 consistently failed tests. 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