Add metric node_ndisc_entries

README.md

@@ -111,6 +111,7 @@ hwmon | sensor | --collector.hwmon.sensor-include | --collector.hwmon.sensor-exc
 infiniband | device | --collector.infiniband.device-include | --collector.infiniband.device-exclude
 interrupts | name | --collector.interrupts.name-include | --collector.interrupts.name-exclude
 netdev | device | --collector.netdev.device-include | --collector.netdev.device-exclude
+ndisc | device | --collector.ndisc.device-include | --collector.ndisc.device-exclude
 qdisc | device | --collector.qdisc.device-include | --collector.qdisc.device-exclude
 slabinfo | slab-names | --collector.slabinfo.slabs-include | --collector.slabinfo.slabs-exclude
 sysctl | all | --collector.sysctl.include | N/A
@@ -150,6 +151,7 @@ netisr | Exposes netisr statistics | FreeBSD
 netstat | Exposes network statistics from `/proc/net/netstat`. This is the same information as `netstat -s`. | Linux
 nfs | Exposes NFS client statistics from `/proc/net/rpc/nfs`. This is the same information as `nfsstat -c`. | Linux
 nfsd | Exposes NFS kernel server statistics from `/proc/net/rpc/nfsd`. This is the same information as `nfsstat -s`. | Linux
+ndisc | Exposes NDISC neighbor statistics. | Linux
 nvme | Exposes NVMe info from `/sys/class/nvme/` | Linux
 os | Expose OS release info from `/etc/os-release` or `/usr/lib/os-release` | _any_
 powersupplyclass | Exposes Power Supply statistics from `/sys/class/power_supply` | Linux

collector/ndisc_linux.go

@@ -0,0 +1,101 @@
+// Copyright 2026 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build !nondisc
+
+package collector
+
+import (
+	"fmt"
+	"log/slog"
+
+	"github.com/alecthomas/kingpin/v2"
+	"github.com/jsimonetti/rtnetlink/v2/rtnl"
+	"github.com/prometheus/client_golang/prometheus"
+	"golang.org/x/sys/unix"
+)
+
+var (
+	ndiscDeviceInclude = kingpin.Flag("collector.ndisc.device-include", "Regexp of ndisc devices to include (mutually exclusive to device-exclude).").String()
+	ndiscDeviceExclude = kingpin.Flag("collector.ndisc.device-exclude", "Regexp of ndisc devices to exclude (mutually exclusive to device-include).").String()
+)
+
+type ndiscCollector struct {
+	deviceFilter deviceFilter
+	logger       *slog.Logger
+}
+
+func init() {
+	registerCollector("ndisc", defaultEnabled, NewNdiscCollector)
+}
+
+var (
+	ndiscEntries = prometheus.NewDesc(
+		prometheus.BuildFQName(namespace, "ndisc", "entries"),
+		"NDISC entries by device",
+		[]string{"device"}, nil,
+	)
+)
+
+// NewNdiscCollector returns a new Collector exposing NDISC stats.
+func NewNdiscCollector(logger *slog.Logger) (Collector, error) {
+	return &ndiscCollector{
+		deviceFilter: newDeviceFilter(*ndiscDeviceExclude, *ndiscDeviceInclude),
+		logger:       logger,
+	}, nil
+}
+
+func getTotalNdiscEntries(neighbors []*rtnl.Neigh) map[string]uint32 {
+	entries := make(map[string]uint32)
+
+	for _, n := range neighbors {
+		if n.State&unix.NUD_NOARP == 0 && n.Interface != nil {
+			entries[n.Interface.Name]++
+		}
+	}
+
+	return entries
+}
+
+func getTotalNdiscEntriesRTNL() (map[string]uint32, error) {
+	conn, err := rtnl.Dial(nil)
+	if err != nil {
+		return nil, err
+	}
+	defer conn.Close()
+
+	neighbors, err := conn.Neighbours(nil, unix.AF_INET6)
+	if err != nil {
+		return nil, err
+	}
+
+	return getTotalNdiscEntries(neighbors), nil
+}
+
+func (c *ndiscCollector) Update(ch chan<- prometheus.Metric) error {
+	enumeratedEntries, err := getTotalNdiscEntriesRTNL()
+	if err != nil {
+		return fmt.Errorf("could not get NDISC entries: %w", err)
+	}
+
+	for device, entryCount := range enumeratedEntries {
+		if c.deviceFilter.ignored(device) {
+			continue
+		}
+		ch <- prometheus.MustNewConstMetric(
+			ndiscEntries, prometheus.GaugeValue, float64(entryCount), device,
+		)
+	}
+
+	return nil
+}

collector/ndisc_linux_test.go

@@ -0,0 +1,44 @@
+// Copyright 2026 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build !nondisc
+
+package collector
+
+import (
+	"net"
+	"testing"
+
+	"github.com/jsimonetti/rtnetlink/v2/rtnl"
+	"golang.org/x/sys/unix"
+)
+
+func TestGetTotalNdiscEntries(t *testing.T) {
+	t.Parallel()
+
+	neighbors := []*rtnl.Neigh{
+		{Interface: &net.Interface{Name: "eth0"}, State: unix.NUD_REACHABLE},
+		{Interface: &net.Interface{Name: "eth0"}, State: unix.NUD_STALE},
+		{Interface: &net.Interface{Name: "eth1"}, State: unix.NUD_DELAY},
+		{Interface: &net.Interface{Name: "eth1"}, State: unix.NUD_NOARP},
+	}
+
+	entries := getTotalNdiscEntries(neighbors)
+
+	if got, want := entries["eth0"], uint32(2); got != want {
+		t.Fatalf("unexpected entry count for eth0: got %d, want %d", got, want)
+	}
+	if got, want := entries["eth1"], uint32(1); got != want {
+		t.Fatalf("unexpected entry count for eth1: got %d, want %d", got, want)
+	}
+}