2026-07-21T20:02:55Z https://drops.dagstuhl.de/oai

oai:drops-oai.dagstuhl.de:25204 2026-03-19T12:59:35Z ddc:004 open_access

Fast Re-Routing in Networks: On the Complexity of Perfect Resilience Bentert, Matthias Ceylan, Esra Hübner, Valentin Schmid, Stefan Srba, Jiří routing in computer networks fast re-route perfect resilience complexity To achieve fast recovery from link failures, most modern communication networks feature fully decentralized fast re-routing mechanisms. These re-routing mechanisms rely on pre-installed static re-routing rules at the nodes (the routers), which depend only on local failure information, namely on the failed links incident to the node. Ideally, a network is perfectly resilient: the re-routing rules ensure that packets are always successfully routed to their destinations as long as the source and the destination are still physically connected in the underlying network after the failures. Unfortunately, there are examples where achieving perfect resilience is not possible. Surprisingly, only very little is known about the algorithmic aspect of when and how perfect resilience can be achieved. We investigate the computational complexity of analyzing such local fast re-routing mechanisms. Our main result is a negative one: we show that even checking whether a given set of static re-routing rules ensures perfect resilience is coNP-complete. Additionally, we investigate other fundamental variations of the problem. In particular, we show that our coNP-completeness proof also applies to scenarios where the re-routing rules have specific patterns (known as skipping in the literature). On the positive side, for scenarios where nodes do not have information about the link from which a packet arrived (the so-called in-port), we present a linear-time algorithm to realize perfect resilience whenever possible (which we show can also be determined in linear time). Schloss Dagstuhl – Leibniz-Zentrum für Informatik Matthias Bentert and Esra Ceylan and Valentin Hübner and Stefan Schmid and Jiří Srba 2026 Is Part Of LIPIcs, Volume 361, 29th International Conference on Principles of Distributed Systems (OPODIS 2025) InProceedings Text doc-type:ResearchArticle publishedVersion application/pdf doi:10.4230/LIPIcs.OPODIS.2025.31 urn:nbn:de:0030-drops-252040 https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2025.31 eng https://creativecommons.org/licenses/by/4.0/legalcode