--- title: Drain Traffic Before Node Maintenance « IS-IS Labs description: A lab exercise demonstrating how to drain traffic from an IS-IS router before performing maintenance, avoiding traffic disruption in a leaf-and-spine fabric.... canonical: https://daily.dev/posts/drain-traffic-before-node-maintenance-is-is-labs-qlui8mtzu twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Drain Traffic Before Node Maintenance « IS-IS Labs | daily.dev og:description: A lab exercise demonstrating how to drain traffic from an IS-IS router before performing maintenance, avoiding traffic disruption in a leaf-and-spine fabric.... og:url: https://daily.dev/posts/drain-traffic-before-node-maintenance-is-is-labs-qlui8mtzu og:image: https://api.daily.dev/og/posts/QLUi8MTZu.png og:image:alt: Drain Traffic Before Node Maintenance « IS-IS Labs 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. # Drain Traffic Before Node Maintenance « IS-IS Labs **[ipSpace.net Blog](https://daily.dev/sources/ipspace)** · 6 min read · 0 upvotes · 0 comments ## Summary A lab exercise demonstrating how to drain traffic from an IS-IS router before performing maintenance, avoiding traffic disruption in a leaf-and-spine fabric. The key technique is setting the IS-IS overload bit on the spine switch being taken offline, which signals all other routers to avoid using it for transit traffic. The post covers the problem of abrupt shutdowns causing traffic disruption, explains the overload bit mechanism (and how it predates OSPF's maximum metric feature), provides FRRouting configuration tasks, validation steps using netlab, and discusses other uses of the overload bit such as startup delay and signaling performance problems. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### How do I drain traffic from an IS-IS router before taking it down for maintenance? Set the IS-IS overload bit on the router being taken offline. When the overload bit is set in the router's LSP, all other routers in the network receive the updated LSP, recompute their best paths, and remove or replace routes that use the overloaded router as a transit hop. The router's own loopback prefixes remain reachable since they are not transit routes. _Network engineers planning IS-IS maintenance windows track techniques like this on daily.dev._ ### What is the IS-IS overload bit and how does it differ from OSPF maximum metric? The IS-IS overload bit is a flag in an IS-IS LSP that tells all other routers to avoid using that router for transit traffic. It predates OSPF's maximum metric functionality. While some IS-IS implementations also support a high-metric approach (e.g., FRRouting's advertise-high-metrics), the overload bit is the canonical IS-IS mechanism and was originally designed to signal that a router has performance problems such as running out of RAM. _Engineers choosing between IS-IS and OSPF for fabric design find protocol comparisons like this on daily.dev._ ### Can the IS-IS overload bit be set per address family in FRRouting? Yes, FRRouting can set the IS-IS overload bit for individual address families. This means you could inadvertently drain only IPv4 traffic while leaving IPv6 traffic flowing through the router if you configure the overload bit only for one family. In a dual-stack network, you must verify that the overload bit is set for both IPv4 and IPv6 address families to fully drain the node. _Teams running dual-stack IS-IS fabrics with FRRouting find operational gotchas like this on daily.dev._ --- [View this post on daily.dev](https://daily.dev/posts/drain-traffic-before-node-maintenance-is-is-labs-qlui8mtzu) ```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":"Drain Traffic Before Node Maintenance « IS-IS Labs","url":"https://daily.dev/posts/drain-traffic-before-node-maintenance-is-is-labs-qlui8mtzu","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/drain-traffic-before-node-maintenance-is-is-labs-qlui8mtzu"},"datePublished":"2026-08-11T08:52:56.181Z","dateModified":"2026-08-11T09:16:02.184Z","description":"A lab exercise demonstrating how to drain traffic from an IS-IS router before performing maintenance, avoiding traffic disruption in a leaf-and-spine fabric....","image":"https://media.daily.dev/image/upload/s--qPvKM23u--/f_auto/v1722860399/public/Placeholder%2009","thumbnailUrl":"https://media.daily.dev/image/upload/s--qPvKM23u--/f_auto/v1722860399/public/Placeholder%2009","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/drain-traffic-before-node-maintenance-is-is-labs-qlui8mtzu","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"","timeRequired":"PT6M"} {"@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":"Drain Traffic Before Node Maintenance « IS-IS Labs"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/drain-traffic-before-node-maintenance-is-is-labs-qlui8mtzu#faq","mainEntity":[{"@type":"Question","name":"How do I drain traffic from an IS-IS router before taking it down for maintenance?","acceptedAnswer":{"@type":"Answer","text":"Set the IS-IS overload bit on the router being taken offline. 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