{"id":100476,"date":"2026-01-23T17:52:09","date_gmt":"2026-01-23T16:52:09","guid":{"rendered":"https:\/\/dyb.fr\/?p=100476"},"modified":"2026-01-23T17:52:09","modified_gmt":"2026-01-23T16:52:09","slug":"cest-quoi-un-hysteresis-anti-flap","status":"publish","type":"post","link":"https:\/\/dyb.eu\/blog\/cest-quoi-un-hysteresis-anti-flap\/","title":{"rendered":"C’est quoi un hysteresis anti-flap ?"},"content":{"rendered":"
\"\"<\/figure>\n\n\n

Un hysteresis anti-flap<\/strong> (ou hyst\u00e9r\u00e9sis anti-basculement<\/em>) est un m\u00e9canisme de stabilit\u00e9<\/strong> utilis\u00e9 en r\u00e9seau\/syst\u00e8mes pour \u00e9viter qu\u2019un \u00e9tat change trop souvent<\/strong> quand une condition est instable ou proche d\u2019un seuil.<\/p>\n\n\n\n

\ud83d\udc49 En clair :
\u00e7a emp\u00eache une bascule ON\/OFF permanente quand un lien \u201cflotte\u201d<\/strong>.<\/p>\n\n\n\n

\n\n\n\n

Le probl\u00e8me : le flapping<\/em><\/h2>\n\n\n\n

Le flap<\/em>, c\u2019est quand une liaison ou une route :<\/p>\n\n\n\n

    \n
  • monte \u2192 descend \u2192 remonte \u2192 redescend\u2026<\/li>\n\n\n\n
  • souvent \u00e0 cause de :\n
      \n
    • pertes de paquets intermittentes<\/li>\n\n\n\n
    • latence variable<\/li>\n\n\n\n
    • micro-coupures<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n

      Exemple concret chez toi (FTTO \/ FTTH) :<\/p>\n\n\n\n

        \n
      • FTTO perd 2\u20133 pings<\/li>\n\n\n\n
      • pfSense bascule sur FTTH<\/li>\n\n\n\n
      • FTTO revient 10 secondes plus tard<\/li>\n\n\n\n
      • pfSense rebascule
        \u27a1\ufe0f R\u00e9sultat : instabilit\u00e9 r\u00e9seau<\/strong>, sessions cass\u00e9es, VPN qui sautent.<\/li>\n<\/ul>\n\n\n\n
        \n\n\n\n

        La solution : l\u2019hysteresis anti-flap<\/h2>\n\n\n\n

        L\u2019hyst\u00e9r\u00e9sis impose deux seuils ou des d\u00e9lais diff\u00e9rents<\/strong> :<\/p>\n\n\n\n

          \n
        • un pour quitter<\/strong> un \u00e9tat<\/li>\n\n\n\n
        • un autre pour y revenir<\/strong><\/li>\n<\/ul>\n\n\n\n

          Exemple simple<\/h3>\n\n\n\n
          Action<\/th>Condition<\/th><\/tr><\/thead>
          Lien d\u00e9clar\u00e9 DOWN<\/td>5 pings perdus cons\u00e9cutifs<\/td><\/tr>
          Lien d\u00e9clar\u00e9 UP<\/td>20 pings OK cons\u00e9cutifs<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

          \u27a1\ufe0f Le lien doit \u00eatre clairement mauvais<\/strong> pour \u00eatre abandonn\u00e9
          \u27a1\ufe0f et clairement stable<\/strong> pour \u00eatre repris<\/p>\n\n\n\n

          \n\n\n\n

          Exemple r\u00e9seau (pfSense \/ multi-WAN)<\/h2>\n\n\n\n

          Sans hysteresis :<\/p>\n\n\n\n

          FTTO \u2193 \u2192 bascule FTTH\nFTTO \u2191 \u2192 rebascule FTTO\nFTTO \u2193 \u2192 bascule FTTH\n<\/code><\/pre>\n\n\n\n
          Avec hysteresis :<\/p>\n\n\n\n
          FTTO \u2193 (confirm\u00e9 sur X secondes) \u2192 bascule FTTH\nFTTO \u2191 mais pas assez longtemps \u2192 on reste sur FTTH\nFTTO \u2191 stable pendant Y secondes \u2192 retour FTTO\n<\/code><\/pre>\n\n\n\n
          \n\n\n\n
          O\u00f9 on retrouve \u00e7a<\/h2>\n\n\n\n
            \n
          • pfSense \/ OPNsense<\/strong>\n
              \n
            • Gateway monitoring<\/li>\n\n\n\n
            • Failover multi-WAN<\/li>\n<\/ul>\n<\/li>\n\n\n\n
            • OSPF \/ BGP<\/strong>\n
                \n
              • timers hello\/dead<\/li>\n\n\n\n
              • dampening<\/li>\n<\/ul>\n<\/li>\n\n\n\n
              • Load balancers<\/strong><\/li>\n\n\n\n
              • HA \/ VRRP \/ CARP<\/strong><\/li>\n\n\n\n
              • Syst\u00e8mes industriels \/ \u00e9lectroniques<\/strong>\n
                  \n
                • thermostats, capteurs<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n
                  \n\n\n\n
                  Termes \u00e9quivalents que tu verras<\/h2>\n\n\n\n
                    \n
                  • Anti-flap<\/em><\/li>\n\n\n\n
                  • Hysteresis<\/em><\/li>\n\n\n\n
                  • Hold-down timer<\/em><\/li>\n\n\n\n
                  • Failback delay<\/em><\/li>\n\n\n\n
                  • Dampening<\/em><\/li>\n<\/ul>\n\n\n\n
                    \n\n\n\n
                    En r\u00e9sum\u00e9<\/h2>\n\n\n\n
                    \ud83d\udc49 Un hysteresis anti-flap = un garde-fou contre les bascules nerveuses<\/strong>
                    \ud83d\udc49 Il sacrifie un peu de r\u00e9activit\u00e9<\/strong> pour beaucoup plus de stabilit\u00e9<\/strong>
                    \ud83d\udc49 Indispensable dans ton cas FTTO \u2194 FTTH + OSPF + WireGuard<\/strong><\/p>\n","protected":false},"excerpt":{"rendered":"
                    Un hysteresis anti-flap (ou hyst\u00e9r\u00e9sis anti-basculement) est un m\u00e9canisme de stabilit\u00e9 utilis\u00e9 en r\u00e9seau\/syst\u00e8mes pour \u00e9viter qu\u2019un \u00e9tat change trop souvent quand une condition est instable ou proche d\u2019un seuil. \ud83d\udc49 En clair :\u00e7a emp\u00eache une bascule ON\/OFF permanente quand un lien \u201cflotte\u201d. Le probl\u00e8me : le flapping Le flap, c\u2019est quand une liaison ou […]<\/p>\n","protected":false},"author":1,"featured_media":100477,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[26,24],"tags":[50,23],"class_list":["post-100476","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-adminsys","category-reseaux","tag-network","tag-pfsense"],"_links":{"self":[{"href":"https:\/\/dyb.eu\/blog\/wp-json\/wp\/v2\/posts\/100476","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/dyb.eu\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/dyb.eu\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/dyb.eu\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/dyb.eu\/blog\/wp-json\/wp\/v2\/comments?post=100476"}],"version-history":[{"count":1,"href":"https:\/\/dyb.eu\/blog\/wp-json\/wp\/v2\/posts\/100476\/revisions"}],"predecessor-version":[{"id":100478,"href":"https:\/\/dyb.eu\/blog\/wp-json\/wp\/v2\/posts\/100476\/revisions\/100478"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/dyb.eu\/blog\/wp-json\/wp\/v2\/media\/100477"}],"wp:attachment":[{"href":"https:\/\/dyb.eu\/blog\/wp-json\/wp\/v2\/media?parent=100476"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/dyb.eu\/blog\/wp-json\/wp\/v2\/categories?post=100476"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/dyb.eu\/blog\/wp-json\/wp\/v2\/tags?post=100476"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}