--- title: IS-IS on Point-to-Point Links « IS-IS Labs | daily.dev description: A hands-on lab exercise explaining why IS-IS point-to-point link mode is strongly preferred over multi-access (LAN) mode on Ethernet interfaces between... canonical: https://daily.dev/posts/is-is-on-point-to-point-links-is-is-labs-ccjwqdmca twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: IS-IS on Point-to-Point Links « IS-IS Labs | daily.dev og:description: A hands-on lab exercise explaining why IS-IS point-to-point link mode is strongly preferred over multi-access (LAN) mode on Ethernet interfaces between... og:url: https://daily.dev/posts/is-is-on-point-to-point-links-is-is-labs-ccjwqdmca og:image: https://api.daily.dev/og/posts/cCJwqdmca.png og:image:alt: IS-IS on Point-to-Point Links « 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. # IS-IS on Point-to-Point Links « IS-IS Labs **[ipSpace.net Blog](https://daily.dev/sources/ipspace)** · 9 min read · 0 upvotes · 0 comments ## Summary A hands-on lab exercise explaining why IS-IS point-to-point link mode is strongly preferred over multi-access (LAN) mode on Ethernet interfaces between routers. Covers the drawbacks of multi-access links: DIS election overhead, extra pseudonode LSPs in the LSPDB, and slower error recovery via CSNP. Walks through inspecting the IS-IS database in both modes using FRRouting CLI output, then explains the three-way handshake (RFC 5303) for P2P adjacency verification, including the Cisco IOSv interoperability caveat requiring explicit `isis three-way-handshake ietf` configuration. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### What are the drawbacks of IS-IS multi-access (LAN) mode compared to point-to-point mode on Ethernet links? IS-IS multi-access mode has three main drawbacks on Ethernet: it requires electing a Designated Intermediate System (DIS), which slows adjacency establishment and convergence after failure; it adds pseudonode LSPs to the LSPDB, increasing database size; and error recovery is slower because IS-IS has no retransmissions — routers detect problems only when the DIS sends CSNP packets, typically every 10 seconds. _Network engineers tuning IS-IS convergence find the latest protocol deep-dives on daily.dev._ ### Why do I need to configure `isis three-way-handshake ietf` on Cisco IOSv when connecting to other IS-IS routers? Cisco IOSv defaults to a pre-standard three-way handshake protocol rather than the IETF version defined in RFC 5303, even though that RFC was published in 2008. Without explicitly setting `isis three-way-handshake ietf`, adjacency with non-Cisco routers can fail in confusing ways — one side may show a fully operational adjacency while the other reports no neighbors. Cisco IOS XE uses the IETF handshake by default. _Catching IS-IS interoperability gotchas before they hit production is easier when routing protocol news lands in one place — daily.dev covers it._ ### What does an IS-IS pseudonode LSP look like and what does it contain? A pseudonode LSP is originated by the Designated Intermediate System (DIS) on a multi-access link. Its LSP ID uses the DIS system ID with a non-zero nodeid octet (e.g., r2.74-00). It contains Extended Reachability TLVs pointing to each connected router with metric 0, but unlike an OSPF type-2 LSA, it does not include the LAN IP prefix — prefixes are advertised in each router's own LSP. _Developers and network engineers tracking IS-IS and routing protocol internals share findings on daily.dev._ ## Similar posts on daily.dev - [Multivendor SR-MPLS « ipSpace.net blog](https://daily.dev/posts/multivendor-sr-mpls-ipspace-net-blog-qekokwduk) · ipSpace.net Blog · 0 upvotes · 0 comments - [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 --- [View this post on daily.dev](https://daily.dev/posts/is-is-on-point-to-point-links-is-is-labs-ccjwqdmca) ```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":"IS-IS on Point-to-Point Links « IS-IS Labs","url":"https://daily.dev/posts/is-is-on-point-to-point-links-is-is-labs-ccjwqdmca","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/is-is-on-point-to-point-links-is-is-labs-ccjwqdmca"},"datePublished":"2026-08-11T08:51:48.187Z","dateModified":"2026-08-11T08:54:29.210Z","description":"A hands-on lab exercise explaining why IS-IS point-to-point link mode is strongly preferred over multi-access (LAN) mode on Ethernet interfaces between...","image":"https://media.daily.dev/image/upload/s--P4t4XyoV--/f_auto/v1722860399/public/Placeholder%2001","thumbnailUrl":"https://media.daily.dev/image/upload/s--P4t4XyoV--/f_auto/v1722860399/public/Placeholder%2001","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/is-is-on-point-to-point-links-is-is-labs-ccjwqdmca","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"","timeRequired":"PT9M"} {"@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":"IS-IS on Point-to-Point Links « IS-IS Labs"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/is-is-on-point-to-point-links-is-is-labs-ccjwqdmca#faq","mainEntity":[{"@type":"Question","name":"What are the drawbacks of IS-IS multi-access (LAN) mode compared to point-to-point mode on Ethernet links?","acceptedAnswer":{"@type":"Answer","text":"IS-IS multi-access mode has three main drawbacks on Ethernet: it requires electing a Designated Intermediate System (DIS), which slows adjacency establishment and convergence after failure; it adds pseudonode LSPs to the LSPDB, increasing database size; and error recovery is slower because IS-IS has no retransmissions — routers detect problems only when the DIS sends CSNP packets, typically every 10 seconds. 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