diff --git a/src/frontend/src/features/diagnostics/checks/selectedCandidate.ts b/src/frontend/src/features/diagnostics/checks/selectedCandidate.ts
index 7ca26699..e41113ea 100644
--- a/src/frontend/src/features/diagnostics/checks/selectedCandidate.ts
+++ b/src/frontend/src/features/diagnostics/checks/selectedCandidate.ts
@@ -42,6 +42,23 @@ export type IceCandidateReport = {
   working: IceCandidatePair[]
 }
 
+/**
+ * True when the selected pair does not carry media over plain UDP: the browser
+ * fell back to a TURN relay over TCP or TLS, or even the direct route is not
+ * UDP. Media still flows, but quality usually degrades under load.
+ *
+ * Accepts the loosely typed `data` stored on the step result; anything that is
+ * not an IceCandidateReport simply yields false.
+ */
+export const isSuboptimalRoute = (data: unknown): boolean => {
+  const selected = (data as IceCandidateReport | null | undefined)?.selected
+  if (!selected) return false
+  const transport = selected.local.relayProtocol ?? selected.local.protocol
+  // An unreported transport is not evidence of a bad route.
+  if (!transport) return false
+  return transport.toLowerCase() !== 'udp'
+}
+
 const PROBE_WIDTH = 320
 const PROBE_HEIGHT = 180
 const PROBE_FPS = 15
diff --git a/src/frontend/src/features/diagnostics/components/ConnectionTestSummary.tsx b/src/frontend/src/features/diagnostics/components/ConnectionTestSummary.tsx
index 7552670d..153225d5 100644
--- a/src/frontend/src/features/diagnostics/components/ConnectionTestSummary.tsx
+++ b/src/frontend/src/features/diagnostics/components/ConnectionTestSummary.tsx
@@ -2,18 +2,33 @@ import type { ReactNode } from 'react'
 import { useTranslation } from 'react-i18next'
 import { ProgressBar } from 'react-aria-components'
 import { css, cx } from '@/styled-system/css'
+import { A } from '@/primitives'
 import type { ConnectionTestStats } from '../types'
 import { statusSquareClass } from './stepAppearance'
 
-type SummaryState = 'idle' | 'running' | 'passed' | 'partial' | 'failed'
+/**
+ * Network prerequisites (protocols, ports, TURN fallbacks), written for the
+ * reader's IT department rather than for the end user.
+ */
+const NETWORK_REQUIREMENTS_DOC_URL =
+  'https://docs.numerique.gouv.fr/docs/f2baa1b9-f29e-4d58-959d-65d4376fc6b8/'
 
-/** Only a failure earns a colour: everything else stays near-black. */
+type SummaryState =
+  | 'idle'
+  | 'running'
+  | 'passed'
+  | 'partial'
+  | 'failed'
+  | 'warning'
+
+/** Only a failure or a degraded route earns a colour: everything else stays near-black. */
 const stateColorClass: Record<SummaryState, string> = {
   idle: css({ color: 'greyscale.1000' }),
   running: css({ color: 'greyscale.1000' }),
   passed: css({ color: 'greyscale.1000' }),
   partial: css({ color: 'greyscale.1000' }),
   failed: css({ color: 'danger.600' }),
+  warning: css({ color: 'warning' }),
 }
 
 const cardClass = css({
@@ -176,23 +191,31 @@ const Counter = ({
 export const ConnectionTestSummary = ({
   stats,
   isRunning,
+  routeWarning = false,
   children,
 }: {
   stats: ConnectionTestStats
   isRunning: boolean
+  /** The selected ICE route is usable but not UDP (e.g. TURN over TCP/TLS). */
+  routeWarning?: boolean
   children?: ReactNode
 }) => {
   const { t } = useTranslation('connectionTest')
 
+  // A hard failure still outranks the route warning; the warning outranks
+  // 'partial' because a measured degraded route matters more than skipped
+  // camera or microphone checks.
   const state: SummaryState = isRunning
     ? 'running'
     : !stats.hasStarted
       ? 'idle'
       : stats.failed > 0
         ? 'failed'
-        : stats.skipped > 0
-          ? 'partial'
-          : 'passed'
+        : routeWarning
+          ? 'warning'
+          : stats.skipped > 0
+            ? 'partial'
+            : 'passed'
 
   return (
     <section className={cardClass}>
@@ -206,7 +229,22 @@ export const ConnectionTestSummary = ({
             : t(`summary.${state}`)}
         </p>
 
-        <p className={hintClass}>{t(`summary.${state}Hint`)}</p>
+        <p className={hintClass}>
+          {t(`summary.${state}Hint`)}
+          {state === 'warning' && (
+            <>
+              {' '}
+              <A
+                href={NETWORK_REQUIREMENTS_DOC_URL}
+                target="_blank"
+                rel="noreferrer"
+                size="sm"
+              >
+                {t('summary.warningDocLink')}
+              </A>
+            </>
+          )}
+        </p>
       </div>
 
       {stats.hasStarted && (
diff --git a/src/frontend/src/features/diagnostics/hooks/useConnectionTestRunner.ts b/src/frontend/src/features/diagnostics/hooks/useConnectionTestRunner.ts
index e0c736ed..467ee345 100644
--- a/src/frontend/src/features/diagnostics/hooks/useConnectionTestRunner.ts
+++ b/src/frontend/src/features/diagnostics/hooks/useConnectionTestRunner.ts
@@ -53,6 +53,9 @@ const fromCheckInfo = (info: CheckInfo): Partial<ConnectionTestStepResult> => ({
   status: CHECK_STATUS_TO_STEP[info.status] ?? 'failed',
   summary: info.description,
   logs: info.logs,
+  // Only SelectedCandidateCheck sets `data` (the ICE candidate report); for
+  // the stock LiveKit checks it is undefined and this is a no-op.
+  data: info.data as Record<string, unknown> | undefined,
 })
 
 const groupDevicesByKind = (devices: MediaDeviceInfo[]) => {
diff --git a/src/frontend/src/features/diagnostics/routes/ConnectionTest.tsx b/src/frontend/src/features/diagnostics/routes/ConnectionTest.tsx
index d4eb3134..de1ab5dd 100644
--- a/src/frontend/src/features/diagnostics/routes/ConnectionTest.tsx
+++ b/src/frontend/src/features/diagnostics/routes/ConnectionTest.tsx
@@ -13,6 +13,7 @@ import { css } from '@/styled-system/css'
 import { Center, VStack } from '@/styled-system/jsx'
 import { Permissions } from '@/features/rooms/components/Permissions'
 import { useConnectionTestRunner } from '../hooks/useConnectionTestRunner'
+import { isSuboptimalRoute } from '../checks/selectedCandidate'
 import { ConnectionTestStepRow } from '../components/ConnectionTestStepRow'
 import { ConnectionTestSummary } from '../components/ConnectionTestSummary'
 import { CONNECTION_TEST_GROUPS, summarizeSteps } from '../types'
@@ -70,6 +71,13 @@ const ConnectionTest = () => {
     () => new Map(steps.map((step) => [step.id, step] as const)),
     [steps]
   )
+  // The summary headline downgrades to a warning when media flows but over a
+  // fallback route: TURN over TCP/TLS, or anything else that is not UDP.
+  const routeWarning = useMemo(() => {
+    const step = stepsById.get('selectedCandidate')
+    return step?.status === 'success' && isSuboptimalRoute(step.data)
+  }, [stepsById])
+
   const isPublishVideoRunning =
     stepsById.get('publishVideo')?.status === 'running'
 
@@ -99,7 +107,11 @@ const ConnectionTest = () => {
       <CenteredContent withBackButton>
         <Center>
           <VStack gap="1.5rem" maxWidth="40rem" width="100%">
-            <ConnectionTestSummary stats={stats} isRunning={isRunning}>
+            <ConnectionTestSummary
+              stats={stats}
+              isRunning={isRunning}
+              routeWarning={routeWarning}
+            >
               {isRunning ? (
                 // A disabled "run" button while the test runs is dead weight:
                 // cancelling is the only thing left to do.
diff --git a/src/frontend/src/locales/de/connectionTest.json b/src/frontend/src/locales/de/connectionTest.json
index 226940f1..b235d64e 100644
--- a/src/frontend/src/locales/de/connectionTest.json
+++ b/src/frontend/src/locales/de/connectionTest.json
@@ -46,6 +46,9 @@
     "passedHint": "Ihr Browser, Ihre Geräte und Ihr Netzwerk sind für eine Besprechung bereit.",
     "partial": "Teilweiser Test",
     "partialHint": "Einige Prüfungen wurden übersprungen. Erlauben Sie den Zugriff auf Ihre Kamera und Ihr Mikrofon, um diese zu testen.",
+    "warning": "Verbindung nicht optimal",
+    "warningHint": "Achtung: Sie befinden sich nicht in optimalen Bedingungen für die Nutzung des Tools. Ihre Medien werden nicht über UDP übertragen (Rückgriff auf ein TURN-Relay über TCP oder TLS), was die Audio- und Videoqualität beeinträchtigen kann.",
+    "warningDocLink": "Technische Dokumentation für Ihre IT-Abteilung",
     "failed_one": "{{count}} Prüfung fehlgeschlagen",
     "failed_other": "{{count}} Prüfungen fehlgeschlagen",
     "failedHint": "Öffnen Sie die fehlgeschlagenen Prüfungen für weitere Details und senden Sie den Bericht an Ihre IT-Abteilung."
diff --git a/src/frontend/src/locales/en/connectionTest.json b/src/frontend/src/locales/en/connectionTest.json
index 8c6868a5..d58e9158 100644
--- a/src/frontend/src/locales/en/connectionTest.json
+++ b/src/frontend/src/locales/en/connectionTest.json
@@ -46,6 +46,9 @@
     "passedHint": "Your browser, your devices and your network are ready for a meeting.",
     "partial": "Partially tested",
     "partialHint": "Some checks were skipped. Allow access to your camera and microphone to test them.",
+    "warning": "Suboptimal connection",
+    "warningHint": "Warning: you are not in optimal conditions to use the tool. Your media is not carried over UDP (it falls back to a TURN relay over TCP or TLS), which can degrade audio and video quality.",
+    "warningDocLink": "Technical documentation for your IT department",
     "failed_one": "{{count}} check failed",
     "failed_other": "{{count}} checks failed",
     "failedHint": "Open the failed checks below for details, then send the report to your IT department."
diff --git a/src/frontend/src/locales/fr/connectionTest.json b/src/frontend/src/locales/fr/connectionTest.json
index 6390122a..ccf00716 100644
--- a/src/frontend/src/locales/fr/connectionTest.json
+++ b/src/frontend/src/locales/fr/connectionTest.json
@@ -46,6 +46,9 @@
     "passedHint": "Votre navigateur, vos périphériques et votre réseau sont prêts pour une réunion.",
     "partial": "Test partiel",
     "partialHint": "Certaines vérifications ont été ignorées. Autorisez l'accès à votre caméra et à votre microphone pour les tester.",
+    "warning": "Connexion non optimale",
+    "warningHint": "Attention : vous n'êtes pas dans les conditions optimales pour accéder à l'outil. Vos flux ne transitent pas en UDP (repli sur un relais TURN en TCP ou TLS), ce qui peut dégrader la qualité audio et vidéo.",
+    "warningDocLink": "Documentation technique à destination de votre service informatique",
     "failed_one": "{{count}} vérification en échec",
     "failed_other": "{{count}} vérifications en échec",
     "failedHint": "Ouvrez les vérifications en échec pour voir le détail, puis transmettez le rapport à votre service informatique."
diff --git a/src/frontend/src/locales/nl/connectionTest.json b/src/frontend/src/locales/nl/connectionTest.json
index 785c629b..5ba53983 100644
--- a/src/frontend/src/locales/nl/connectionTest.json
+++ b/src/frontend/src/locales/nl/connectionTest.json
@@ -46,6 +46,9 @@
     "passedHint": "Je browser, apparaten en netwerk zijn klaar voor een vergadering.",
     "partial": "Gedeeltelijke test",
     "partialHint": "Sommige controles zijn overgeslagen. Geef toegang tot je camera en microfoon om deze te testen.",
+    "warning": "Verbinding niet optimaal",
+    "warningHint": "Let op: je bevindt je niet in optimale omstandigheden om de tool te gebruiken. Je media loopt niet via UDP (terugval op een TURN-relay via TCP of TLS), wat de audio- en videokwaliteit kan verminderen.",
+    "warningDocLink": "Technische documentatie voor je IT-afdeling",
     "failed_one": "{{count}} controle mislukt",
     "failed_other": "{{count}} controles mislukt",
     "failedHint": "Open de mislukte controles voor meer details en stuur het rapport door naar je IT-afdeling."