From cc3d84b97e53f1b073bcad133902aa11e38bfc13 Mon Sep 17 00:00:00 2001
From: Ian Gulliver <git@flamingcow.io>
Date: Sat, 24 Jan 2026 23:11:55 -0800
Subject: [PATCH] Query DHCP binding table from Netgear switches via SNMP

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
---
 snmp.go | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)

diff --git a/snmp.go b/snmp.go
index 1fb1e5f..0909d0a 100644
--- a/snmp.go
+++ b/snmp.go
@@ -111,6 +111,7 @@ func (t *Tendrils) querySNMPDevice(node *Node, ip net.IP) {
 	t.queryInterfaceStats(snmp, node, ifNames)
 	t.queryPoEBudget(snmp, node)
 	t.queryBridgeMIB(snmp, node, ifNames)
+	t.queryDHCPBindings(snmp)
 }
 
 func (t *Tendrils) querySysName(snmp *gosnmp.GoSNMP, node *Node) {
@@ -469,3 +470,63 @@ func (t *Tendrils) getInterfaceNames(snmp *gosnmp.GoSNMP) map[int]string {
 
 	return names
 }
+
+func (t *Tendrils) queryDHCPBindings(snmp *gosnmp.GoSNMP) {
+	baseOID := "1.3.6.1.4.1.4526.10.12.3.2.1"
+	ipOID := baseOID + ".1"
+	macOID := baseOID + ".3"
+
+	ipResults, err := snmp.BulkWalkAll(ipOID)
+	if err != nil {
+		return
+	}
+
+	macResults, err := snmp.BulkWalkAll(macOID)
+	if err != nil {
+		return
+	}
+
+	ips := map[int]net.IP{}
+	for _, result := range ipResults {
+		if result.Type != gosnmp.IPAddress {
+			continue
+		}
+		oidSuffix := strings.TrimPrefix(strings.TrimPrefix(result.Name, "."+ipOID), ".")
+		var idx int
+		if _, err := fmt.Sscanf(oidSuffix, "%d", &idx); err != nil {
+			continue
+		}
+		ips[idx] = net.ParseIP(result.Value.(string))
+	}
+
+	macs := map[int]net.HardwareAddr{}
+	for _, result := range macResults {
+		if result.Type != gosnmp.OctetString {
+			continue
+		}
+		macBytes := result.Value.([]byte)
+		if len(macBytes) != 6 {
+			continue
+		}
+		oidSuffix := strings.TrimPrefix(strings.TrimPrefix(result.Name, "."+macOID), ".")
+		var idx int
+		if _, err := fmt.Sscanf(oidSuffix, "%d", &idx); err != nil {
+			continue
+		}
+		macs[idx] = net.HardwareAddr(macBytes)
+	}
+
+	for idx, ip := range ips {
+		mac, ok := macs[idx]
+		if !ok {
+			continue
+		}
+		if isBroadcastOrZero(mac) {
+			continue
+		}
+		if t.DebugSNMP {
+			log.Printf("[snmp] %s: dhcp binding mac=%s ip=%s", snmp.Target, mac, ip)
+		}
+		t.nodes.Update(nil, mac, []net.IP{ip}, "", "", "dhcp")
+	}
+}