diff --git a/cmd/dhcp4d/dhcp4d.go b/cmd/dhcp4d/dhcp4d.go
index 7d4b79d..6babb70 100644
--- a/cmd/dhcp4d/dhcp4d.go
+++ b/cmd/dhcp4d/dhcp4d.go
@@ -389,7 +389,7 @@ func newSrv(permDir string) (*srv, error) {
 		if err := json.Indent(&out, b, "", "\t"); err == nil {
 			b = out.Bytes()
 		}
-		if err := renameio.WriteFile(filepath.Join(permDir, "dhcp4d/leases.json"), out.Bytes(), 0644); err != nil {
+		if err := renameio.WriteFile(filepath.Join(permDir, "dhcp4d/leases.json"), b, 0644); err != nil {
 			errs <- err
 		}
 		updateNonExpired(leases)
diff --git a/integration/radvd/radvd_test.go b/integration/radvd/radvd_test.go
index bf23f5d..82c2e46 100644
--- a/integration/radvd/radvd_test.go
+++ b/integration/radvd/radvd_test.go
@@ -15,6 +15,7 @@
 package integration_test
 
 import (
+	"fmt"
 	"io/ioutil"
 	"net"
 	"os"
@@ -80,7 +81,7 @@ func TestRouterAdvertisement(t *testing.T) {
 	}
 	go func() {
 		if err := srv.Serve("veth2a", conn); err != nil {
-			t.Fatal(err)
+			panic(fmt.Sprintf("failed to serve router advertisements: %v", err))
 		}
 	}()
 	//time.Sleep(5 * time.Second)
diff --git a/internal/dhcp4/dhcp4.go b/internal/dhcp4/dhcp4.go
index 25796e7..5c99b80 100644
--- a/internal/dhcp4/dhcp4.go
+++ b/internal/dhcp4/dhcp4.go
@@ -100,7 +100,7 @@ func (c *Client) ObtainOrRenew() bool {
 			c.connection = conn
 		}
 		if c.connection == nil && c.Interface == nil {
-			onceErr = fmt.Errorf("Interface is nil")
+			onceErr = fmt.Errorf("c.Interface is nil")
 			return
 		}
 		if c.hardwareAddr == nil && c.HWAddr != nil {
diff --git a/internal/dhcp4d/dhcp4d_test.go b/internal/dhcp4d/dhcp4d_test.go
index 95cfd0f..522f2dd 100644
--- a/internal/dhcp4d/dhcp4d_test.go
+++ b/internal/dhcp4d/dhcp4d_test.go
@@ -15,7 +15,6 @@
 package dhcp4d
 
 import (
-	"bytes"
 	"io/ioutil"
 	"net"
 	"os"
@@ -112,7 +111,7 @@ func TestLease(t *testing.T) {
 			t.Fatalf("unexpected number of leases: got %d, want %d", got, want)
 		}
 		l := leases[0]
-		if got, want := l.Addr, addr; !bytes.Equal(got, want) {
+		if got, want := l.Addr, addr; !got.Equal(want) {
 			t.Fatalf("unexpected lease.Addr: got %v, want %v", got, want)
 		}
 		if got, want := l.HardwareAddr, hardwareAddr.String(); got != want {
@@ -155,7 +154,7 @@ func TestPreferredAddress(t *testing.T) {
 	t.Run("no requested IP", func(t *testing.T) {
 		p := request(net.IPv4zero, hardwareAddr)
 		resp := handler.serveDHCP(p, dhcp4.Discover, p.ParseOptions())
-		if got, want := resp.YIAddr().To4(), addr.To4(); bytes.Equal(got, want) {
+		if got, want := resp.YIAddr().To4(), addr.To4(); got.Equal(want) {
 			t.Errorf("DHCPOFFER for wrong IP: got %v, want anything else", got)
 		}
 	})
@@ -163,7 +162,7 @@ func TestPreferredAddress(t *testing.T) {
 	t.Run("requested CIAddr", func(t *testing.T) {
 		p := request(addr, hardwareAddr)
 		resp := handler.serveDHCP(p, dhcp4.Discover, p.ParseOptions())
-		if got, want := resp.YIAddr().To4(), addr.To4(); !bytes.Equal(got, want) {
+		if got, want := resp.YIAddr().To4(), addr.To4(); !got.Equal(want) {
 			t.Errorf("DHCPOFFER for wrong IP: got %v, want %v", got, want)
 		}
 	})
@@ -188,7 +187,7 @@ func TestPreferredAddress(t *testing.T) {
 			},
 		)
 		resp := handler.serveDHCP(p, dhcp4.Discover, p.ParseOptions())
-		if got, want := resp.YIAddr().To4(), addr.To4(); !bytes.Equal(got, want) {
+		if got, want := resp.YIAddr().To4(), addr.To4(); !got.Equal(want) {
 			t.Errorf("DHCPOFFER for wrong IP: got %v, want %v", got, want)
 		}
 	})
@@ -227,7 +226,7 @@ func TestPreviousLease(t *testing.T) {
 
 	p := request(addr1, hardwareAddr1)
 	resp := handler.serveDHCP(p, dhcp4.Request, p.ParseOptions())
-	if got, want := resp.YIAddr().To4(), addr1.To4(); !bytes.Equal(got, want) {
+	if got, want := resp.YIAddr().To4(), addr1.To4(); !got.Equal(want) {
 		t.Errorf("DHCPREQUEST resulted in wrong IP: got %v, want %v", got, want)
 	}
 
@@ -239,21 +238,21 @@ func TestPreviousLease(t *testing.T) {
 
 	p = discover(net.IPv4zero, hardwareAddr1)
 	resp = handler.serveDHCP(p, dhcp4.Discover, p.ParseOptions())
-	if got, want := resp.YIAddr().To4(), addr1.To4(); !bytes.Equal(got, want) {
+	if got, want := resp.YIAddr().To4(), addr1.To4(); !got.Equal(want) {
 		t.Errorf("DHCPOFFER for wrong IP: got %v, want %v", got, want)
 	}
 
 	// Free addr1 by requesting addr2
 	p = request(addr2, hardwareAddr1)
 	resp = handler.serveDHCP(p, dhcp4.Request, p.ParseOptions())
-	if got, want := resp.YIAddr().To4(), addr2.To4(); !bytes.Equal(got, want) {
+	if got, want := resp.YIAddr().To4(), addr2.To4(); !got.Equal(want) {
 		t.Errorf("DHCPREQUEST resulted in wrong IP: got %v, want %v", got, want)
 	}
 
 	// Verify addr1 is now available to other clients
 	p = request(addr1, hardwareAddr2)
 	resp = handler.serveDHCP(p, dhcp4.Request, p.ParseOptions())
-	if got, want := resp.YIAddr().To4(), addr1.To4(); !bytes.Equal(got, want) {
+	if got, want := resp.YIAddr().To4(), addr1.To4(); !got.Equal(want) {
 		t.Errorf("DHCPREQUEST resulted in wrong IP: got %v, want %v", got, want)
 	}
 }
@@ -279,7 +278,7 @@ func TestPermanentLease(t *testing.T) {
 
 	p := request(addr, hardwareAddr)
 	resp := handler.serveDHCP(p, dhcp4.Request, p.ParseOptions())
-	if got, want := resp.YIAddr().To4(), addr.To4(); !bytes.Equal(got, want) {
+	if got, want := resp.YIAddr().To4(), addr.To4(); !got.Equal(want) {
 		t.Errorf("DHCPREQUEST resulted in wrong IP: got %v, want %v", got, want)
 	}
 
@@ -312,7 +311,7 @@ func TestExpiration(t *testing.T) {
 			hardwareAddr[len(hardwareAddr)-1] = addr[len(addr)-1]
 			p := request(addr, hardwareAddr)
 			resp := handler.serveDHCP(p, dhcp4.Request, p.ParseOptions())
-			if got, want := resp.YIAddr().To4(), addr.To4(); !bytes.Equal(got, want) {
+			if got, want := resp.YIAddr().To4(), addr.To4(); !got.Equal(want) {
 				t.Errorf("DHCPREQUEST resulted in wrong IP: got %v, want %v", got, want)
 			}
 		}
@@ -325,7 +324,7 @@ func TestExpiration(t *testing.T) {
 			hardwareAddr[len(hardwareAddr)-1] = addr[len(addr)-1]
 			p := request(addr, hardwareAddr)
 			resp := handler.serveDHCP(p, dhcp4.Request, p.ParseOptions())
-			if got, want := resp.YIAddr().To4(), addr.To4(); !bytes.Equal(got, want) {
+			if got, want := resp.YIAddr().To4(), addr.To4(); !got.Equal(want) {
 				t.Errorf("DHCPREQUEST resulted in wrong IP: got %v, want %v", got, want)
 			}
 		}
@@ -359,7 +358,7 @@ func TestExpiration(t *testing.T) {
 			addr[len(addr)-1] = byte(1 + (i % 254)) // avoid .0 (net) and .255 (broadcast)
 			p := request(addr, hardwareAddr)
 			resp := handler.serveDHCP(p, dhcp4.Request, p.ParseOptions())
-			if got, want := resp.YIAddr().To4(), addr.To4(); !bytes.Equal(got, want) {
+			if got, want := resp.YIAddr().To4(), addr.To4(); !got.Equal(want) {
 				t.Errorf("DHCPREQUEST resulted in wrong IP: got %v, want %v", got, want)
 			}
 		}
@@ -408,7 +407,7 @@ func TestRequestExpired(t *testing.T) {
 	t.Run("mbp requests any", func(t *testing.T) {
 		p := request(addr, hardwareAddr["mbp"])
 		resp := handler.serveDHCP(p, dhcp4.Discover, p.ParseOptions())
-		if got, want := resp.YIAddr().To4(), addr.To4(); bytes.Equal(got, want) {
+		if got, want := resp.YIAddr().To4(), addr.To4(); got.Equal(want) {
 			t.Errorf("DHCPOFFER for wrong IP: got offered %v (in use!)", got)
 		}
 	})
@@ -452,7 +451,7 @@ func TestPersistentStorage(t *testing.T) {
 
 	p := request(net.IPv4zero, hardwareAddr)
 	resp := handler.serveDHCP(p, dhcp4.Discover, p.ParseOptions())
-	if got, want := resp.YIAddr().To4(), addr.To4(); !bytes.Equal(got, want) {
+	if got, want := resp.YIAddr().To4(), addr.To4(); !got.Equal(want) {
 		t.Errorf("DHCPOFFER for wrong IP: got %v, want %v", got, want)
 	}
 }
diff --git a/internal/dhcp6/dhcp6.go b/internal/dhcp6/dhcp6.go
index 7048b2c..739e73a 100644
--- a/internal/dhcp6/dhcp6.go
+++ b/internal/dhcp6/dhcp6.go
@@ -168,7 +168,7 @@ const maxUDPReceivedPacketSize = 8192 // arbitrary size. Theoretically could be
 
 func (c *Client) sendReceive(packet *dhcpv6.Message, expectedType dhcpv6.MessageType) (*dhcpv6.Message, error) {
 	if packet == nil {
-		return nil, fmt.Errorf("Packet to send cannot be nil")
+		return nil, fmt.Errorf("packet to send cannot be nil")
 	}
 	if expectedType == dhcpv6.MessageTypeNone {
 		// infer the expected type from the packet being sent
diff --git a/internal/dns/dns.go b/internal/dns/dns.go
index b48fbac..dc7d83d 100644
--- a/internal/dns/dns.go
+++ b/internal/dns/dns.go
@@ -327,7 +327,7 @@ func isLocalInAddrArpa(q string) bool {
 	return local
 }
 
-var sentinelEmpty = errors.New("no answers")
+var errEmpty = errors.New("no answers")
 
 func (s *Server) resolve(q dns.Question) (rr dns.RR, err error) {
 	if q.Qclass != dns.ClassINET {
@@ -350,7 +350,7 @@ func (s *Server) resolve(q dns.Question) (rr dns.RR, err error) {
 			if q.Qtype == dns.TypeA {
 				return dns.NewRR(q.Name + " 3600 IN A " + host)
 			}
-			return nil, sentinelEmpty
+			return nil, errEmpty
 		}
 	}
 	if q.Qtype == dns.TypePTR {
@@ -373,7 +373,7 @@ func (s *Server) handleInternal(w dns.ResponseWriter, r *dns.Msg) {
 	}
 	rr, err := s.resolve(r.Question[0])
 	if err != nil {
-		if err == sentinelEmpty {
+		if err == errEmpty {
 			m := new(dns.Msg)
 			m.SetReply(r)
 			w.WriteMsg(m)
@@ -457,7 +457,7 @@ func (s *Server) resolveSubname(hostname string, q dns.Question) (dns.RR, error)
 			if q.Qtype == dns.TypeA {
 				return dns.NewRR(q.Name + " 3600 IN A " + host)
 			}
-			return nil, sentinelEmpty
+			return nil, errEmpty
 		}
 
 		if ip, ok := s.subname(hostname, name); ok {
@@ -467,7 +467,7 @@ func (s *Server) resolveSubname(hostname string, q dns.Question) (dns.RR, error)
 			if q.Qtype == dns.TypeAAAA && ip.To4() == nil {
 				return dns.NewRR(q.Name + " 3600 IN AAAA " + ip.String())
 			}
-			return nil, sentinelEmpty
+			return nil, errEmpty
 		}
 	}
 	return nil, nil
@@ -481,7 +481,7 @@ func (s *Server) subnameHandler(hostname string) func(w dns.ResponseWriter, r *d
 
 		rr, err := s.resolveSubname(hostname, r.Question[0])
 		if err != nil {
-			if err == sentinelEmpty {
+			if err == errEmpty {
 				m := new(dns.Msg)
 				m.SetReply(r)
 				w.WriteMsg(m)
diff --git a/internal/dns/dns_test.go b/internal/dns/dns_test.go
index c278cab..7700716 100644
--- a/internal/dns/dns_test.go
+++ b/internal/dns/dns_test.go
@@ -15,7 +15,6 @@
 package dns
 
 import (
-	"bytes"
 	"fmt"
 	"io/ioutil"
 	"net"
@@ -412,7 +411,7 @@ func TestLocalhost(t *testing.T) {
 		if _, ok := a.(*dns.AAAA); !ok {
 			t.Fatalf("unexpected response type: got %T, want dns.A", a)
 		}
-		if got, want := a.(*dns.AAAA).AAAA, (net.ParseIP("::1")); !bytes.Equal(got, want) {
+		if got, want := a.(*dns.AAAA).AAAA, (net.ParseIP("::1")); !got.Equal(want) {
 			t.Fatalf("unexpected response IP: got %v, want %v", got, want)
 		}
 	})
diff --git a/internal/netconfig/netconfig.go b/internal/netconfig/netconfig.go
index 77ad720..53637d2 100644
--- a/internal/netconfig/netconfig.go
+++ b/internal/netconfig/netconfig.go
@@ -238,6 +238,9 @@ func applyInterfaces(dir, root string) error {
 		byName[details.Name] = details
 	}
 	links, err := netlink.LinkList()
+	if err != nil {
+		return err
+	}
 	for _, l := range links {
 		attr := l.Attrs()
 		// TODO: prefix log line with details about the interface.
diff --git a/internal/radvd/radvd.go b/internal/radvd/radvd.go
index 07966cb..742c06d 100644
--- a/internal/radvd/radvd.go
+++ b/internal/radvd/radvd.go
@@ -16,13 +16,11 @@
 package radvd
 
 import (
-	"encoding/binary"
 	"log"
 	"net"
 	"sync"
 	"time"
 
-	"github.com/google/gopacket/layers"
 	"github.com/mdlayher/ndp"
 
 	"golang.org/x/net/ipv6"
@@ -118,69 +116,6 @@ func (s *Server) ListenAndServe(ifname string) error {
 	return s.Serve(ifname, conn)
 }
 
-type sourceLinkLayerAddress struct {
-	address net.HardwareAddr
-}
-
-func (o sourceLinkLayerAddress) Marshal() layers.ICMPv6Option {
-	return layers.ICMPv6Option{
-		Type: layers.ICMPv6OptSourceAddress,
-		Data: o.address,
-	}
-}
-
-type mtu struct {
-	mtu uint32
-}
-
-func (o mtu) Marshal() layers.ICMPv6Option {
-	buf := make([]byte, 6)
-	// First 2 bytes are reserved
-	binary.BigEndian.PutUint32(buf[2:], o.mtu)
-	return layers.ICMPv6Option{
-		Type: layers.ICMPv6OptMTU,
-		Data: buf,
-	}
-}
-
-type prefixInfo struct {
-	prefixLength      byte
-	flags             byte   // TODO: enum for values
-	validLifetime     uint32 // seconds
-	preferredLifetime uint32 // seconds
-	prefix            [16]byte
-}
-
-func (o prefixInfo) Marshal() layers.ICMPv6Option {
-	buf := make([]byte, 30)
-	buf[0] = o.prefixLength
-	buf[1] = o.flags
-	binary.BigEndian.PutUint32(buf[2:], o.validLifetime)
-	binary.BigEndian.PutUint32(buf[6:], o.preferredLifetime)
-	// 4 bytes reserved
-	copy(buf[14:], o.prefix[:])
-	return layers.ICMPv6Option{
-		Type: layers.ICMPv6OptPrefixInfo,
-		Data: buf,
-	}
-}
-
-type rdnss struct {
-	lifetime uint32 // seconds
-	server   []byte
-}
-
-func (o rdnss) Marshal() layers.ICMPv6Option {
-	buf := make([]byte, 22)
-	// 2 bytes reserved
-	binary.BigEndian.PutUint32(buf[2:], o.lifetime)
-	copy(buf[6:], o.server[:])
-	return layers.ICMPv6Option{
-		Type: 25, // TODO: Recursive DNS Server
-		Data: buf,
-	}
-}
-
 var ipv6LinkLocal = func(cidr string) *net.IPNet {
 	_, net, err := net.ParseCIDR(cidr)
 	if err != nil {
diff --git a/internal/testing/dnsmasq/dnsmasq.go b/internal/testing/dnsmasq/dnsmasq.go
index f3217c1..ba696ba 100644
--- a/internal/testing/dnsmasq/dnsmasq.go
+++ b/internal/testing/dnsmasq/dnsmasq.go
@@ -116,7 +116,7 @@ func Run(t *testing.T, iface, ns string) *Process {
 		case <-p.done:
 			return // test done, any errors are from our Kill()
 		default:
-			t.Fatalf("dnsmasq exited prematurely: %v", err)
+			panic(fmt.Sprintf("dnsmasq exited prematurely: %v", err))
 		}
 	}()