add per-node mac table populated from snmp and arp

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

arp.go

@@ -36,6 +36,8 @@ type arpEntry struct {
 func (t *Tendrils) readARPTable() {
 	entries := t.parseARPTable()
 
+	localNode := t.getLocalNode()
+
 	for _, entry := range entries {
 		if t.Interface != "" && entry.iface != t.Interface {
 			continue
@@ -49,6 +51,9 @@ func (t *Tendrils) readARPTable() {
 		}
 
 		t.nodes.Update(nil, entry.mac, []net.IP{entry.ip}, "", "", "arp")
+		if localNode != nil {
+			t.nodes.UpdateMACTable(localNode, entry.mac, entry.iface)
+		}
 	}
 }
 

nodes.go

@@ -42,6 +42,7 @@ func (i *Interface) String() string {
 type Node struct {
 	Name       string
 	Interfaces map[string]*Interface
+	MACTable   map[string]string // peer MAC -> local interface name
 }
 
 func (n *Node) String() string {
@@ -118,6 +119,7 @@ func (n *Nodes) Update(target *Node, mac net.HardwareAddr, ips []net.IP, ifaceNa
 		n.nextID++
 		n.nodes[targetID] = &Node{
 			Interfaces: map[string]*Interface{},
+			MACTable:   map[string]string{},
 		}
 		isNew = true
 	}
@@ -263,6 +265,13 @@ func (n *Nodes) mergeNodes(keepID, mergeID int) {
 		n.macIndex[iface.MAC.String()] = keepID
 	}
 
+	for peerMAC, ifaceName := range merge.MACTable {
+		if keep.MACTable == nil {
+			keep.MACTable = map[string]string{}
+		}
+		keep.MACTable[peerMAC] = ifaceName
+	}
+
 	delete(n.nodes, mergeID)
 }
 
@@ -286,6 +295,16 @@ func (n *Nodes) GetByMAC(mac net.HardwareAddr) *Node {
 	return nil
 }
 
+func (n *Nodes) UpdateMACTable(node *Node, peerMAC net.HardwareAddr, ifaceName string) {
+	n.mu.Lock()
+	defer n.mu.Unlock()
+
+	if node.MACTable == nil {
+		node.MACTable = map[string]string{}
+	}
+	node.MACTable[peerMAC.String()] = ifaceName
+}
+
 func (n *Nodes) logNode(node *Node) {
 	name := node.Name
 	if name == "" {
@@ -303,6 +322,10 @@ func (n *Nodes) logNode(node *Node) {
 		iface := node.Interfaces[ifaceKey]
 		log.Printf("[node]   %s", iface)
 	}
+
+	if len(node.MACTable) > 0 {
+		log.Printf("[node]   mac table: %d entries", len(node.MACTable))
+	}
 }
 
 func (n *Nodes) All() []*Node {

snmp.go

@@ -124,7 +124,7 @@ func (t *Tendrils) querySNMPDevice(node *Node, ip net.IP) {
 
 	t.querySysName(snmp, node)
 	t.queryInterfaceMACs(snmp, node)
-	t.queryBridgeMIB(snmp, ip)
+	t.queryBridgeMIB(snmp, node)
 }
 
 func (t *Tendrils) querySysName(snmp *gosnmp.GoSNMP, node *Node) {
@@ -192,7 +192,7 @@ func (t *Tendrils) queryInterfaceMACs(snmp *gosnmp.GoSNMP, node *Node) {
 	}
 }
 
-func (t *Tendrils) queryBridgeMIB(snmp *gosnmp.GoSNMP, deviceIP net.IP) {
+func (t *Tendrils) queryBridgeMIB(snmp *gosnmp.GoSNMP, node *Node) {
 	portOID := "1.3.6.1.2.1.17.7.1.2.2.1.2"
 
 	portResults, err := snmp.BulkWalkAll(portOID)
@@ -238,19 +238,18 @@ func (t *Tendrils) queryBridgeMIB(snmp *gosnmp.GoSNMP, deviceIP net.IP) {
 			continue
 		}
 
+		ifIndex, exists := bridgePortToIfIndex[entry.bridgePort]
+		if !exists {
+			ifIndex = entry.bridgePort
+		}
+		ifName := rewritePortName(ifNames[ifIndex])
+
 		if t.DebugSNMP {
-			ifIndex, exists := bridgePortToIfIndex[entry.bridgePort]
-			if !exists {
-				ifIndex = entry.bridgePort
-			}
-			ifName := ifNames[ifIndex]
-			if ifName == "" {
-				ifName = "??"
-			}
-			log.Printf("[snmp] %s: mac=%s port=%s", deviceIP, mac, ifName)
+			log.Printf("[snmp] %s: mac=%s port=%s", snmp.Target, mac, ifName)
 		}
 
 		t.nodes.Update(nil, mac, nil, "", "", "snmp")
+		t.nodes.UpdateMACTable(node, mac, ifName)
 	}
 }
 

tendrils.go

@@ -97,6 +97,22 @@ func (t *Tendrils) populateLocalAddresses() {
 	}
 }
 
+func (t *Tendrils) getLocalNode() *Node {
+	interfaces, err := net.Interfaces()
+	if err != nil {
+		return nil
+	}
+
+	for _, iface := range interfaces {
+		if len(iface.HardwareAddr) > 0 {
+			if node := t.nodes.GetByMAC(iface.HardwareAddr); node != nil {
+				return node
+			}
+		}
+	}
+	return nil
+}
+
 func (t *Tendrils) listInterfaces() []net.Interface {
 	interfaces, err := net.Interfaces()
 	if err != nil {