Pull request 2741: AGDNS-3863-gopacket-dhcp-vol.34

Updates #4923.

Squashed commit of the following:

commit ac803e041ccc2d635031479a143fc1afd93921eb
Merge: 7c4263837 b0e930c6b
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Aug 4 19:35:57 2026 +0300

    Merge branch 'master' into AGDNS-3863-gopacket-dhcp-vol.34

commit 7c4263837388c51bdf33acabbca7ab0d7ae7d8ac
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Aug 4 19:09:44 2026 +0300

    dhcpsvc: don't consider zero iaid invalid

commit d883e64b91089dd0a2369e6e537b89c984c0d106
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Aug 4 17:35:56 2026 +0300

    dhcpsvc: imp maint

commit 947a9b34f9f0e07c6a895f55163757a85eb684b6
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Aug 4 15:35:14 2026 +0300

    dhcpsvc: impl dhcpv6 release

internal/dhcpsvc/dhcpsvc_test.go

@@ -393,27 +393,19 @@ func (db *testDatabase) Store(ctx context.Context, leases []*dhcpsvc.Lease) (err
 	return db.onStore(ctx, leases)
 }
 
-// newTestDatabase creates a new *testDatabase for testing.  If initial is not
-// nil, db.Load is set to return it.  By default, db.Store panics on any call.
-func newTestDatabase(tb testing.TB, initial []*dhcpsvc.Lease) (db *testDatabase) {
+// newTestDatabase creates a new *testDatabase for testing.  The Load method
+// returns [testLeases], and the Store method panics.
+func newTestDatabase(tb testing.TB) (db *testDatabase) {
 	tb.Helper()
 
-	db = &testDatabase{
-		onLoad: func(ctx context.Context) (_ []*dhcpsvc.Lease, _ error) {
-			panic(testutil.UnexpectedCall(ctx))
+	return &testDatabase{
+		onLoad: func(_ context.Context) (leases []*dhcpsvc.Lease, err error) {
+			return testLeases, nil
 		},
 		onStore: func(ctx context.Context, leases []*dhcpsvc.Lease) (_ error) {
 			panic(testutil.UnexpectedCall(ctx, leases))
 		},
 	}
-
-	if initial != nil {
-		db.onLoad = func(ctx context.Context) (leases []*dhcpsvc.Lease, err error) {
-			return initial, nil
-		}
-	}
-
-	return db
 }
 
 // newTestDHCPServer creates a new DHCPServer for testing.  It uses the default

internal/dhcpsvc/handler4_test.go

@@ -83,7 +83,7 @@ func TestDHCPServer_ServeEther4_discover(t *testing.T) {
 
 			ndMgr, inCh, outCh := newTestNetworkDeviceManager(t, testIfaceAddrV4)
 			startTestDHCPServer(t, &dhcpsvc.Config{
-				Database:             newTestDatabase(t, testLeases),
+				Database:             newTestDatabase(t),
 				Interfaces:           testIPv4InterfacesConf,
 				NetworkDeviceManager: ndMgr,
 				Enabled:              true,
@@ -105,7 +105,7 @@ func TestDHCPServer_ServeEther4_discoverExpired(t *testing.T) {
 	ndMgr, inCh, outCh := newTestNetworkDeviceManager(t, testIfaceAddrV4)
 
 	startTestDHCPServer(t, &dhcpsvc.Config{
-		Database:             newTestDatabase(t, testLeases),
+		Database:             newTestDatabase(t),
 		Interfaces:           testIPv4InterfacesConf,
 		NetworkDeviceManager: ndMgr,
 		Enabled:              true,
@@ -156,7 +156,7 @@ func TestDHCPServer_ServeEther4_release(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Parallel()
 
-			db := newTestDatabase(t, testLeases)
+			db := newTestDatabase(t)
 
 			onStore := func(ctx context.Context, leases []*dhcpsvc.Lease) (err error) {
 				assert.NotContains(testutil.NewPanicT(t), leases, tc.want)
@@ -262,7 +262,7 @@ func TestDHCPServer_ServeEther4_requestSelecting(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Parallel()
 
-			db := newTestDatabase(t, testLeases)
+			db := newTestDatabase(t)
 
 			onStore := func(ctx context.Context, leases []*dhcpsvc.Lease) (err error) {
 				assert.Contains(t, leases, tc.want)
@@ -311,7 +311,7 @@ func TestDHCPServer_ServeEther4_requestSelectingNoLease(t *testing.T) {
 		flags:        dhcpsvc.FlagsBroadcast,
 	})
 
-	db := newTestDatabase(t, testLeases)
+	db := newTestDatabase(t)
 
 	ndMgr, inCh, outCh := newTestNetworkDeviceManager(t, testIfaceAddrV4)
 	startTestDHCPServer(t, &dhcpsvc.Config{
@@ -413,7 +413,7 @@ func TestDHCPServer_ServeEther4_requestInitReboot(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Parallel()
 
-			db := newTestDatabase(t, testLeases)
+			db := newTestDatabase(t)
 
 			onStore := func(ctx context.Context, leases []*dhcpsvc.Lease) (err error) {
 				assert.Contains(t, leases, tc.want)
@@ -513,7 +513,7 @@ func TestDHCPServer_ServeEther4_requestRenewSuccess(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Parallel()
 
-			db := newTestDatabase(t, testLeases)
+			db := newTestDatabase(t)
 
 			onStore := func(ctx context.Context, leases []*dhcpsvc.Lease) (err error) {
 				assert.Contains(t, leases, tc.want)
@@ -586,7 +586,7 @@ func TestDHCPServer_ServeEther4_requestRenewFail(t *testing.T) {
 			}
 
 			startTestDHCPServer(t, &dhcpsvc.Config{
-				Database:             newTestDatabase(t, testLeases),
+				Database:             newTestDatabase(t),
 				Interfaces:           testIPv4InterfacesConf,
 				NetworkDeviceManager: ndMgr,
 				Enabled:              true,
@@ -641,7 +641,7 @@ func TestDHCPServer_ServeEther4_decline(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Parallel()
 
-			db := newTestDatabase(t, testLeases)
+			db := newTestDatabase(t)
 
 			onStore := func(ctx context.Context, leases []*dhcpsvc.Lease) (err error) {
 				assert.Contains(t, leases, wantLease)

internal/dhcpsvc/handler6.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"fmt"
+	"net/netip"
 
 	"github.com/AdguardTeam/golibs/errors"
 	"github.com/AdguardTeam/golibs/logutil/slogutil"
@@ -377,7 +378,8 @@ func (iface *dhcpInterfaceV6) handleInfo(
 // handleRelease handles messages of type RELEASE.  req must not be nil and must
 // be a valid DHCPv6 message of type RELEASE.  fd must be valid.
 //
-// TODO(e.burkov):  Implement.  This is a stub for now.
+// TODO(e.burkov):  Verify all IA_NA options instead of handling only the first
+// one.
 func (iface *dhcpInterfaceV6) handleRelease(
 	ctx context.Context,
 	fd *frameData6,
@@ -391,7 +393,43 @@ func (iface *dhcpInterfaceV6) handleRelease(
 	l := iface.common.logger
 	l.DebugContext(ctx, "handling message", "type", req.MsgType, "cli_id", cliID)
 
-	return nil
+	resp := &layers.DHCPv6{
+		MsgType:       layers.DHCPv6MsgTypeReply,
+		TransactionID: req.TransactionID,
+	}
+
+	iaid, ip := iface.ipForRelease(ctx, req)
+	if ip == (netip.Addr{}) {
+		resp.Options = iface.newUpdateRespOpts(fd, req, cliID, layers.DHCPv6Option{})
+
+		return respond6(fd, resp)
+	}
+
+	key := macToKey(fd.ether.SrcMAC)
+
+	iface.common.indexMu.Lock()
+	defer iface.common.indexMu.Unlock()
+
+	lease, hasLease := iface.common.leases[key]
+	if !hasLease || lease.IP != ip {
+		respIANA := newIANAWithStatus(iaid, layers.DHCPv6StatusCodeNoBinding)
+		resp.Options = iface.newUpdateRespOpts(fd, req, cliID, respIANA)
+
+		return respond6(fd, resp)
+	}
+
+	err = iface.common.index.remove(ctx, lease, iface.common)
+	if err != nil {
+		l.ErrorContext(ctx, "removing lease", slogutil.KeyError, err)
+
+		respIANA := newIANAWithStatus(iaid, layers.DHCPv6StatusCodeNoBinding)
+		resp.Options = iface.newUpdateRespOpts(fd, req, cliID, respIANA)
+	} else {
+		respIANA := &IANAOption{ID: iaid}
+		resp.Options = iface.newUpdateRespOpts(fd, req, cliID, respIANA.Encode())
+	}
+
+	return respond6(fd, resp)
 }
 
 // handleDecline handles messages of type DECLINE.  req must not be nil and must

internal/dhcpsvc/handler6_test.go

@@ -91,7 +91,7 @@ func TestDHCPServer_ServeEther6_solicit(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Parallel()
 
-			db := newTestDatabase(t, testLeases)
+			db := newTestDatabase(t)
 
 			ndMgr, inCh, outCh := newTestNetworkDeviceManager(t, testIfaceAddrV6)
 			startTestDHCPServer(t, &dhcpsvc.Config{
@@ -185,7 +185,7 @@ func TestDHCPServer_ServeEther6_solicitRapidCommit(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Parallel()
 
-			db := newTestDatabase(t, testLeases)
+			db := newTestDatabase(t)
 
 			onStore := func(ctx context.Context, leases []*dhcpsvc.Lease) (err error) {
 				assert.Contains(t, leases, tc.want)
@@ -280,7 +280,7 @@ func TestDHCPServer_ServeEther6_request(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Parallel()
 
-			db := newTestDatabase(t, testLeases)
+			db := newTestDatabase(t)
 
 			onStore := func(ctx context.Context, leases []*dhcpsvc.Lease) (err error) {
 				assert.Contains(t, leases, tc.want)
@@ -361,7 +361,7 @@ func TestDHCPServer_ServeEther6_requestWithSolicit(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Parallel()
 
-			db := newTestDatabase(t, testLeases)
+			db := newTestDatabase(t)
 
 			onStore := func(ctx context.Context, leases []*dhcpsvc.Lease) (err error) {
 				assert.Contains(t, leases, tc.want)
@@ -469,7 +469,7 @@ func TestDHCPServer_ServeEther6_confirm(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Parallel()
 
-			db := newTestDatabase(t, testLeases)
+			db := newTestDatabase(t)
 
 			ndMgr, inCh, outCh := newTestNetworkDeviceManager(t, testIfaceAddrV6)
 			startTestDHCPServer(t, &dhcpsvc.Config{
@@ -543,7 +543,7 @@ func TestDHCPServer_ServeEther6_renew(t *testing.T) {
 	for _, tc := range testCases {
 		req := testutil.RequireTypeAssert[*layers.DHCPv6](t, tc.in.Layer(layers.LayerTypeDHCPv6))
 
-		db := newTestDatabase(t, testLeases)
+		db := newTestDatabase(t)
 
 		onStore := func(ctx context.Context, leases []*dhcpsvc.Lease) (err error) {
 			assert.Contains(t, leases, tc.want)
@@ -630,7 +630,7 @@ func TestDHCPServer_ServeEther6_rebind(t *testing.T) {
 	for _, tc := range testCases {
 		req := testutil.RequireTypeAssert[*layers.DHCPv6](t, tc.in.Layer(layers.LayerTypeDHCPv6))
 
-		db := newTestDatabase(t, testLeases)
+		db := newTestDatabase(t)
 
 		onStore := func(ctx context.Context, leases []*dhcpsvc.Lease) (err error) {
 			assert.Contains(t, leases, tc.want)
@@ -699,10 +699,108 @@ func TestDHCPServer_ServeEther6_info(t *testing.T) {
 	for _, tc := range testCases {
 		req := testutil.RequireTypeAssert[*layers.DHCPv6](t, tc.in.Layer(layers.LayerTypeDHCPv6))
 
+		db := newTestDatabase(t)
+
 		t.Run(tc.name, func(t *testing.T) {
 			t.Parallel()
 
-			db := newTestDatabase(t, testLeases)
+			ndMgr, inCh, outCh := newTestNetworkDeviceManager(t, testIfaceAddrV6)
+			startTestDHCPServer(t, &dhcpsvc.Config{
+				Database:             db,
+				Interfaces:           testIPv6InterfacesConf,
+				Logger:               testLogger,
+				NetworkDeviceManager: ndMgr,
+				Enabled:              true,
+			})
+
+			testutil.RequireSend(t, inCh, tc.in, testTimeout)
+
+			assertValidResponse6(t, req, outCh, tc.wantOpts)
+		})
+	}
+}
+
+func TestDHCPServer_ServeEther6_release(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		in       gopacket.Packet
+		want     *dhcpsvc.Lease
+		name     string
+		wantOpts layers.DHCPv6Options
+	}{{
+		in:   newDHCPv6Release(t, testHWDynamic, testIPv6Dynamic),
+		want: testLease6Dynamic,
+		name: "success",
+		wantOpts: layers.DHCPv6Options{
+			newOptServerDUID(t, testIfaceHWAddr),
+			newOptClientDUID(t, testHWDynamic),
+			newOptIANAStatus(t, testIAID, layers.DHCPv6StatusCodeSuccess),
+			newOptPreference(t, 0),
+			newOptSolMaxRT(t, dhcpsvc.DefaultSolMaxRT),
+		},
+	}, {
+		in:   newDHCPv6Release(t, testHWStatic, testIPv6Static),
+		want: testLease6Static,
+		name: "success_static",
+		wantOpts: layers.DHCPv6Options{
+			newOptServerDUID(t, testIfaceHWAddr),
+			newOptClientDUID(t, testHWStatic),
+			newOptIANAStatus(t, testIAID, layers.DHCPv6StatusCodeSuccess),
+			newOptPreference(t, 0),
+			newOptSolMaxRT(t, dhcpsvc.DefaultSolMaxRT),
+		},
+	}, {
+		in:   newDHCPv6Release(t, testHWUnknown, testIPv6Unknown),
+		want: nil,
+		name: "no_binding",
+		wantOpts: layers.DHCPv6Options{
+			newOptServerDUID(t, testIfaceHWAddr),
+			newOptClientDUID(t, testHWUnknown),
+			newOptIANAStatus(t, testIAID, layers.DHCPv6StatusCodeNoBinding),
+			newOptPreference(t, 0),
+			newOptSolMaxRT(t, dhcpsvc.DefaultSolMaxRT),
+		},
+	}, {
+		in:   newDHCPv6Release(t, testHWDynamic, netip.Addr{}),
+		want: nil,
+		name: "no_iana",
+		wantOpts: layers.DHCPv6Options{
+			newOptServerDUID(t, testIfaceHWAddr),
+			newOptClientDUID(t, testHWDynamic),
+			newOptPreference(t, 0),
+			newOptSolMaxRT(t, dhcpsvc.DefaultSolMaxRT),
+		},
+	}, {
+		in:   newDHCPv6Release(t, testHWDynamic, testIPv6Unknown),
+		want: nil,
+		name: "ip_mismatch",
+		wantOpts: layers.DHCPv6Options{
+			newOptServerDUID(t, testIfaceHWAddr),
+			newOptClientDUID(t, testHWDynamic),
+			newOptIANAStatus(t, testIAID, layers.DHCPv6StatusCodeNoBinding),
+			newOptPreference(t, 0),
+			newOptSolMaxRT(t, dhcpsvc.DefaultSolMaxRT),
+		},
+	}}
+
+	for _, tc := range testCases {
+		req := testutil.RequireTypeAssert[*layers.DHCPv6](t, tc.in.Layer(layers.LayerTypeDHCPv6))
+
+		db := newTestDatabase(t)
+
+		onStore := func(ctx context.Context, leases []*dhcpsvc.Lease) (err error) {
+			assert.NotContains(t, leases, tc.want)
+
+			return nil
+		}
+
+		if tc.want != nil {
+			db.onStore = onStore
+		}
+
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
 
 			ndMgr, inCh, outCh := newTestNetworkDeviceManager(t, testIfaceAddrV6)
 			startTestDHCPServer(t, &dhcpsvc.Config{
@@ -1036,3 +1134,31 @@ func newDHCPv6Renew(tb testing.TB, mac net.HardwareAddr, reqIP netip.Addr) (pkt
 
 	return newTestPacket(tb, layers.LinkTypeEthernet, eth, ip, udp, dhcp)
 }
+
+// newDHCPv6Release creates a new DHCPv6 RELEASE packet for testing.
+func newDHCPv6Release(tb testing.TB, mac net.HardwareAddr, reqIP netip.Addr) (pkt gopacket.Packet) {
+	tb.Helper()
+
+	eth := newEthernetLayer(tb, mac, testIfaceHWAddr, layers.EthernetTypeIPv6)
+	ip, udp := newIPv6UDPLayer(tb, netip.AddrPort{}, netip.AddrPort{})
+
+	dhcp := &layers.DHCPv6{
+		MsgType:  layers.DHCPv6MsgTypeRelease,
+		HopCount: 0,
+		// Don't specify link and peer addresses, as they are intended for relay
+		// messages.
+		LinkAddr:      nil,
+		PeerAddr:      nil,
+		TransactionID: testTransactionID,
+		Options: layers.DHCPv6Options{
+			newOptClientDUID(tb, mac),
+			newOptServerDUID(tb, testIfaceHWAddr),
+		},
+	}
+
+	if reqIP.IsValid() && reqIP.Is6() {
+		dhcp.Options = append(dhcp.Options, newOptIANA(tb, testIAID, reqIP, testLeaseTTL))
+	}
+
+	return newTestPacket(tb, layers.LinkTypeEthernet, eth, ip, udp, dhcp)
+}

internal/dhcpsvc/leaseindex.go

@@ -97,11 +97,7 @@ func (idx *leaseIndex) add(l *Lease, iface *netInterface) (err error) {
 // remove removes l from idx and from iface.  l must be valid, iface should
 // contain the same lease or the lease itself.  It returns an error if the lease
 // not found.
-func (idx *leaseIndex) remove(
-	ctx context.Context,
-	l *Lease,
-	iface *netInterface,
-) (err error) {
+func (idx *leaseIndex) remove(ctx context.Context, l *Lease, iface *netInterface) (err error) {
 	loweredName := strings.ToLower(l.Hostname)
 
 	if _, ok := idx.byAddr[l.IP]; !ok {

internal/dhcpsvc/server_test.go

@@ -94,7 +94,7 @@ func TestDHCPServer_AddLease(t *testing.T) {
 				return nil
 			}
 
-			db := newTestDatabase(t, testLeases)
+			db := newTestDatabase(t)
 			if tc.wantErrMsg == "" {
 				db.onStore = onStore
 			}
@@ -116,7 +116,7 @@ func TestDHCPServer_index(t *testing.T) {
 	t.Parallel()
 
 	srv := newTestDHCPServer(t, &dhcpsvc.Config{
-		Database: newTestDatabase(t, testLeases),
+		Database: newTestDatabase(t),
 		Enabled:  true,
 	})
 
@@ -244,7 +244,7 @@ func TestDHCPServer_UpdateStaticLease(t *testing.T) {
 				return nil
 			}
 
-			db := newTestDatabase(t, testLeases)
+			db := newTestDatabase(t)
 			if tc.wantErrMsg == "" {
 				db.onStore = onStore
 			}
@@ -319,7 +319,7 @@ func TestDHCPServer_RemoveLease(t *testing.T) {
 				return nil
 			}
 
-			db := newTestDatabase(t, testLeases)
+			db := newTestDatabase(t)
 			if tc.wantErrMsg == "" {
 				db.onStore = onStore
 			}
@@ -340,7 +340,7 @@ func TestDHCPServer_RemoveLease(t *testing.T) {
 func TestDHCPServer_Reset(t *testing.T) {
 	t.Parallel()
 
-	db := newTestDatabase(t, testLeases)
+	db := newTestDatabase(t)
 	db.onStore = func(_ context.Context, leases []*dhcpsvc.Lease) (err error) {
 		assert.Empty(t, leases)
 
@@ -364,7 +364,7 @@ func TestServer_Leases(t *testing.T) {
 	t.Parallel()
 
 	srv := newTestDHCPServer(t, &dhcpsvc.Config{
-		Database: newTestDatabase(t, testLeases),
+		Database: newTestDatabase(t),
 		Enabled:  true,
 	})
 

internal/dhcpsvc/v6.go

@@ -403,6 +403,7 @@ func (iface *dhcpInterfaceV6) allocateForSolicit(
 ) (lease *Lease, iaid uint32) {
 	l := iface.common.logger
 	key := macToKey(mac)
+	now := iface.clock.Now()
 
 	for i, reqOpt := range req.Options {
 		if reqOpt.Code != layers.DHCPv6OptIANA {
@@ -417,12 +418,14 @@ func (iface *dhcpInterfaceV6) allocateForSolicit(
 			continue
 		}
 
+		// TODO(e.burkov):  Check if the IA actually requests any address.
+
 		var ok bool
 		if lease, ok = iface.common.leases[key]; ok {
 			return lease, iana.ID
 		}
 
-		lease, err = iface.common.allocateLease(ctx, mac, key, iface.clock.Now())
+		lease, err = iface.common.allocateLease(ctx, mac, key, now)
 		if err != nil {
 			l.DebugContext(ctx, "no address available", "iaid", iana.ID, slogutil.KeyError, err)
 
@@ -437,6 +440,41 @@ func (iface *dhcpInterfaceV6) allocateForSolicit(
 	return nil, 0
 }
 
+// ipForRelease returns the IAID and IP address requested for release in req.
+// It returns zero values if there is no IA_NA option or if all options are
+// malformed.  req must be a valid DHCPv6 message of RELEASE type.
+func (iface *dhcpInterfaceV6) ipForRelease(
+	ctx context.Context,
+	req *layers.DHCPv6,
+) (iaid uint32, ip netip.Addr) {
+	l := iface.common.logger
+
+	for i, reqOpt := range req.Options {
+		if reqOpt.Code != layers.DHCPv6OptIANA {
+			continue
+		}
+
+		iana := &IANAOption{}
+		err := iana.UnmarshalBinary(reqOpt.Data)
+		if err != nil {
+			l.DebugContext(ctx, "malformed ia_na", "idx", i, slogutil.KeyError, err)
+
+			continue
+		}
+
+		reqIP, hasReqIP := iana.requestedAddr()
+		if !hasReqIP {
+			l.DebugContext(ctx, "no ip in ia_na for release", "iaid", iana.ID)
+
+			continue
+		}
+
+		return iana.ID, reqIP
+	}
+
+	return 0, netip.Addr{}
+}
+
 // firstIANA returns the first valid IA_NA option in req.  It returns false if
 // there is no such option.  req must not be nil.
 func (iface *dhcpInterfaceV6) firstIANA(
@@ -502,10 +540,10 @@ func (iface *dhcpInterfaceV6) confirmAddrsOnLink(
 }
 
 // newSolicitRespOpts returns the common option list for Advertise and
-// rapid-commit Reply responses to a Solicit request.  Zero iaid creates an
+// rapid-commit Reply responses to a Solicit request.  Nil lease creates an
 // option with Status Code NoAddrsAvail.  rapidCommit defines whether the
-// response should include the Rapid Commit option.  fd, req, cliID, and lease
-// must not be nil.
+// response should include the Rapid Commit option.  fd, req, and cliID must not
+// be nil.
 func (iface *dhcpInterfaceV6) newSolicitRespOpts(
 	fd *frameData6,
 	req *layers.DHCPv6,
@@ -519,7 +557,7 @@ func (iface *dhcpInterfaceV6) newSolicitRespOpts(
 
 	// For Solicit without IA_NA options, respond with safe Advertise with no
 	// IA_NA options and Status Code NoAddrsAvail.
-	if iaid == 0 {
+	if lease == nil {
 		opts = append(opts, newStatusCodeOption(layers.DHCPv6StatusCodeNoAddrsAvail))
 	} else {
 		opts = append(opts, iface.iaNAFromLease(lease, iaid))
@@ -541,7 +579,8 @@ func (iface *dhcpInterfaceV6) newSolicitRespOpts(
 
 // newRequestRespOpts returns the common option list for Reply responses to a
 // Request message.  fd, req, and cliID must not be nil.  iana must be a valid
-// IA_NA option, or be empty if the response should not contain an IA_NA option.
+// IA_NA option, or have a zero code if the response should not contain an IA_NA
+// option.
 //
 // TODO(e.burkov):  Keep the Reply option set aligned with the current Advertise
 // response shape until the wider DHCPv6 implementation is completed.
@@ -595,11 +634,16 @@ func (iface *dhcpInterfaceV6) newConfirmRespOpts(
 	return iface.appendRequestedOptions(opts, req)
 }
 
-// newUpdateRespOpts returns the common option list for Reply responses to a
-// RENEW or REBIND messages.  fd, req, and cliID must not be nil.  iana must be
-// a valid IA_NA option, or empty if the response should not include one.
+// newUpdateRespOpts returns the common option list for Reply responses to
+// RENEW, REBIND, and RELEASE messages.  fd, req, and cliID must not be nil.
+// iana must be a valid IA_NA option, or have a zero code if the response should
+// not include one.
 //
 // See RFC 9915 Section 18.3.4.
+//
+// TODO(e.burkov):  DRY with other options builders
+//
+// TODO(e.burkov):  Use internal types for options.
 func (iface *dhcpInterfaceV6) newUpdateRespOpts(
 	fd *frameData6,
 	req *layers.DHCPv6,