diff --git a/dhcpv4/client.go b/dhcpv4/client.go
index e517ab7..a5bbbe4 100644
--- a/dhcpv4/client.go
+++ b/dhcpv4/client.go
@@ -17,6 +17,7 @@ import (
 type Client struct {
 	connID      uint64
 	reqHostname string
+	clientID    []byte
 	hostname    []byte
 	dns         []netip.Addr
 
@@ -26,6 +27,7 @@ type Client struct {
 	tIPLease   uint32
 	currentXID uint32
 	state      ClientState
+	clientMAC  [6]byte
 	offer      addr4
 	svip       addr4 // OptServerIdentification.
 	siip       addr4 // SIAddr.
@@ -34,7 +36,6 @@ type Client struct {
 	subnet     addr4
 	broadcast  addr4
 	gateway    addr4
-	clientMAC  [6]byte
 
 	auxbuf [64]byte
 }
@@ -78,7 +79,7 @@ func (c *Client) BeginRequest(xid uint32, cfg RequestConfig) error {
 	if len(cfg.Hostname) > 36 {
 		return errors.New("requested hostname too long")
 	} else if c.state != StateInit && c.state != 0 {
-		return errors.New("dhcp client must be closed/done before new request")
+		return errors.New("dhcp client must be closed/Init before new request")
 	} else if xid == 0 {
 		return errors.New("zero xid")
 	}
@@ -88,6 +89,11 @@ func (c *Client) BeginRequest(xid uint32, cfg RequestConfig) error {
 	c.reqHostname = cfg.Hostname
 	c.reqIP = addr4{addr: cfg.RequestedAddr, valid: true}
 	c.clientMAC = cfg.ClientHardwareAddr
+	if cfg.ClientID != "" {
+		c.clientID = append(c.clientID[:0], cfg.ClientID...)
+	} else {
+		c.clientID = append(c.clientID[:0], c.clientMAC[:]...)
+	}
 	return nil
 }
 
@@ -172,7 +178,7 @@ func (c *Client) Encapsulate(carrierFrame []byte, frameOffset int) (int, error)
 	default:
 		return 0, errors.New("unhandled state" + c.state.String())
 	}
-	n, _ := EncodeOption(opts[numOpts:], OptClientIdentifier, c.clientMAC[:]...)
+	n, _ := EncodeOption(opts[numOpts:], OptClientIdentifier, c.clientID...)
 	numOpts += n
 	if len(c.reqHostname) > 0 {
 		n, err := EncodeOptionString(opts[numOpts:], OptHostName, c.reqHostname)
@@ -323,6 +329,7 @@ func (c *Client) reset(xid uint32) {
 		currentXID:  xid,
 		reqIP:       c.reqIP,
 		clientMAC:   c.clientMAC,
+		clientID:    c.clientID,
 	}
 }
 
diff --git a/internet/stackbasic_test.go b/internet/stackbasic_test.go
index bb7f4e2..c431653 100644
--- a/internet/stackbasic_test.go
+++ b/internet/stackbasic_test.go
@@ -117,7 +117,7 @@ func setupClientServer(t *testing.T, rng *rand.Rand, client, server *StackIP, co
 	if err != nil {
 		t.Fatal(err)
 	}
-	err = connClient.OpenActive(svip, clip.Port(), 100)
+	err = connClient.OpenActive(clip.Port(), svip, 100)
 	if err != nil {
 		t.Fatal(err)
 	}
diff --git a/tcp/conn.go b/tcp/conn.go
index d2a4d4c..2c68035 100644
--- a/tcp/conn.go
+++ b/tcp/conn.go
@@ -15,7 +15,9 @@ import (
 )
 
 var (
-	errDeadlineExceeded = os.ErrDeadlineExceeded
+	errDeadlineExceeded    = os.ErrDeadlineExceeded
+	errNoRemoteAddr        = errors.New("tcp: no remote address established")
+	errMismatchedIPVersion = errors.New("mismatched IP version")
 )
 
 // Conn builds on the [Handler] abstraction and adds IP header knowledge, time management, and familiar user facing API
@@ -27,14 +29,12 @@ type Conn struct {
 	h          Handler
 	remoteAddr []byte
 
-	rdead  time.Time
-	wdead  time.Time
-	lastTx time.Time
-	lastRx time.Time
-
-	ipID     uint16
+	rdead    time.Time
+	wdead    time.Time
 	abortErr error
 	logger
+
+	ipID uint16
 }
 
 type ConnConfig struct {
@@ -69,7 +69,7 @@ func (conn *Conn) BufferedInput() int { return conn.h.BufferedInput() }
 
 // OpenActive opens a connection to a remote peer with a known IP address and port combination.
 // iss is the initial send sequence number which is ideally a random number which is far away from the last sequence number used on a connection to the same host.
-func (conn *Conn) OpenActive(remote netip.AddrPort, localPort uint16, iss Value) error {
+func (conn *Conn) OpenActive(localPort uint16, remote netip.AddrPort, iss Value) error {
 	err := conn.h.OpenActive(localPort, remote.Port(), iss)
 	if err != nil {
 		return err
@@ -214,13 +214,13 @@ func (conn *Conn) Demux(buf []byte, off int) (err error) {
 
 func (conn *Conn) Encapsulate(buf []byte, off int) (n int, err error) {
 	if len(conn.remoteAddr) == 0 {
-		return 0, errors.New("unset IP address")
+		return 0, errNoRemoteAddr
 	}
 	raddr, _, _, _, err := internal.GetIPAddr(buf[:off])
 	if err != nil {
 		return 0, err
 	} else if len(raddr) != len(conn.remoteAddr) {
-		return 0, errors.New("mismatched IP version")
+		return 0, errMismatchedIPVersion
 	}
 	n, err = conn.h.Send(buf[off:])
 	if err != nil {