Fix switch-to-switch link detection by finding all valid last hops

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

link.go

@@ -76,30 +76,36 @@ func (n *Nodes) getDirectLinks() []*Link {
 			}
 			seenMACs[mac] = true
 
-			lastHop, lastPort := n.findLastHop(target, mac, macToNode)
-			if lastHop == nil {
-				continue
-			}
-
-			targetIface := n.findTargetInterface(target, lastHop, macToNode)
-			key := makeLinkKey(lastHop, lastPort, target, targetIface)
+			lastHops := n.findAllLastHops(target, mac, macToNode)
+			for _, lh := range lastHops {
+				targetIface := n.findTargetInterface(target, lh.node, macToNode)
+				key := makeLinkKey(lh.node, lh.port, target, targetIface)
 				if !seen[key] {
 					seen[key] = true
 					links = append(links, &Link{
 						TypeID:     newTypeID("link"),
-					NodeA:      lastHop,
-					InterfaceA: lastPort,
+						NodeA:      lh.node,
+						InterfaceA: lh.port,
 						NodeB:      target,
 						InterfaceB: targetIface,
 					})
 				}
 			}
 		}
+	}
 
 	return links
 }
 
-func (n *Nodes) findLastHop(target *Node, mac string, macToNode map[string]*Node) (*Node, string) {
+func (n *Nodes) findAllLastHops(target *Node, mac string, macToNode map[string]*Node) []struct {
+	node *Node
+	port string
+} {
+	var results []struct {
+		node *Node
+		port string
+	}
+
 	for _, node := range n.nodes {
 		port, sees := node.MACTable[mac]
 		if !sees || node == target {
@@ -107,10 +113,13 @@ func (n *Nodes) findLastHop(target *Node, mac string, macToNode map[string]*Node
 		}
 
 		if !n.hasCloserNode(node, target, mac, port, macToNode) {
-			return node, port
+			results = append(results, struct {
+				node *Node
+				port string
+			}{node, port})
 		}
 	}
-	return nil, ""
+	return results
 }
 
 func (n *Nodes) hasCloserNode(node, target *Node, mac, port string, macToNode map[string]*Node) bool {

static/index.html

@@ -112,6 +112,19 @@
             white-space: nowrap;
         }
 
+        .node .root-label {
+            position: absolute;
+            top: -8px;
+            left: 50%;
+            transform: translateX(-50%);
+            font-size: 9px;
+            background: #664;
+            color: #ffa;
+            padding: 1px 6px;
+            border-radius: 8px;
+            white-space: nowrap;
+        }
+
         .node:hover {
             filter: brightness(1.2);
         }
@@ -277,7 +290,12 @@
             labelEl.textContent = getLabel(node);
             div.appendChild(labelEl);
 
-            if (isSwitch(node) && uplinkInfo) {
+            if (isSwitch(node) && uplinkInfo === 'ROOT') {
+                const rootEl = document.createElement('div');
+                rootEl.className = 'root-label';
+                rootEl.textContent = 'ROOT';
+                div.appendChild(rootEl);
+            } else if (isSwitch(node) && uplinkInfo) {
                 const uplinkEl = document.createElement('div');
                 uplinkEl.className = 'uplink';
                 uplinkEl.textContent = uplinkInfo.localPort + ' → ' + uplinkInfo.parentName + ':' + uplinkInfo.remotePort;
@@ -447,10 +465,18 @@
                     });
                 });
 
-                let bestRoot = allSwitches[0];
+                for (const edges of adjacency.values()) {
+                    edges.sort((a, b) => getLabel(a.neighbor).localeCompare(getLabel(b.neighbor)));
+                }
+
+                const sortedSwitches = [...allSwitches].sort((a, b) =>
+                    getLabel(a).localeCompare(getLabel(b)));
+
+                let bestRoot = sortedSwitches[0];
+                let bestReachable = 0;
                 let bestMaxDepth = Infinity;
 
-                allSwitches.forEach(candidate => {
+                for (const candidate of sortedSwitches) {
                     const visited = new Set([candidate.typeid]);
                     const queue = [{ sw: candidate, depth: 0 }];
                     let maxDepth = 0;
@@ -466,11 +492,16 @@
                         }
                     }
 
-                    if (maxDepth < bestMaxDepth) {
+                    const reachable = visited.size;
+                    if (reachable > bestReachable ||
+                        (reachable === bestReachable && maxDepth < bestMaxDepth)) {
+                        bestReachable = reachable;
                         bestMaxDepth = maxDepth;
                         bestRoot = candidate;
                     }
-                });
+                }
+
+                switchUplinks.set(bestRoot.typeid, 'ROOT');
 
                 const visited = new Set([bestRoot.typeid]);
                 const queue = [bestRoot];
@@ -489,6 +520,7 @@
                         }
                     }
                 }
+
             }
 
             const container = document.getElementById('container');