diff --git a/core/client/client.go b/core/client/client.go
index 26336f2..161265f 100644
--- a/core/client/client.go
+++ b/core/client/client.go
@@ -24,6 +24,9 @@ import (
 
 const (
 	udpMessageChanSize = 1024
+
+	closeErrCodeOK            = 0x100 // HTTP3 ErrCodeNoError
+	closeErrCodeProtocolError = 0x101 // HTTP3 ErrCodeGeneralProtocolError
 )
 
 type Client interface {
@@ -179,13 +182,13 @@ func (c *clientImpl) connect() (quic.Connection, func(), error) {
 	resp, err := rt.RoundTrip(req)
 	if err != nil {
 		if conn != nil {
-			_ = conn.CloseWithError(0, "")
+			_ = conn.CloseWithError(closeErrCodeProtocolError, "")
 		}
 		_ = pktConn.Close()
 		return nil, nil, &coreErrs.ConnectError{Err: err}
 	}
 	if resp.StatusCode != protocol.StatusAuthOK {
-		_ = conn.CloseWithError(0, "")
+		_ = conn.CloseWithError(closeErrCodeProtocolError, "")
 		_ = pktConn.Close()
 		return nil, nil, &coreErrs.AuthError{StatusCode: resp.StatusCode}
 	}
@@ -206,7 +209,7 @@ func (c *clientImpl) connect() (quic.Connection, func(), error) {
 	go c.udpLoop(conn)
 
 	return conn, func() {
-		_ = conn.CloseWithError(0, "")
+		_ = conn.CloseWithError(closeErrCodeOK, "")
 		_ = pktConn.Close()
 	}, nil
 }
diff --git a/core/server/server.go b/core/server/server.go
index ecfbcef..48c5fcc 100644
--- a/core/server/server.go
+++ b/core/server/server.go
@@ -18,6 +18,11 @@ import (
 	"github.com/quic-go/quic-go/http3"
 )
 
+const (
+	closeErrCodeOK                  = 0x100 // HTTP3 ErrCodeNoError
+	closeErrCodeTrafficLimitReached = 0x107 // HTTP3 ErrCodeExcessiveLoad
+)
+
 type Server interface {
 	Serve() error
 	Close() error
@@ -85,7 +90,7 @@ func (s *serverImpl) handleClient(conn quic.Connection) {
 	if handler.authenticated && s.config.EventLogger != nil {
 		s.config.EventLogger.Disconnect(conn.RemoteAddr(), handler.authID, err)
 	}
-	_ = conn.CloseWithError(0, "")
+	_ = conn.CloseWithError(closeErrCodeOK, "")
 }
 
 type h3sHandler struct {
@@ -281,7 +286,7 @@ func (h *h3sHandler) handleTCPRequest(stream quic.Stream) {
 	_ = stream.Close()
 	// Disconnect the client if TrafficLogger requested
 	if err == errDisconnect {
-		_ = h.conn.CloseWithError(0, "")
+		_ = h.conn.CloseWithError(closeErrCodeTrafficLimitReached, "")
 	}
 }
 
@@ -323,7 +328,7 @@ func (h *h3sHandler) handleUDPRequest(stream quic.Stream) {
 					ok := h.config.TrafficLogger.Log(h.authID, 0, uint64(udpN))
 					if !ok {
 						// TrafficLogger requested to disconnect the client
-						_ = h.conn.CloseWithError(0, "")
+						_ = h.conn.CloseWithError(closeErrCodeTrafficLimitReached, "")
 						return
 					}
 				}
@@ -383,7 +388,7 @@ func (h *h3sHandler) udpLoop() {
 		ok := h.handleUDPMessage(msg)
 		if !ok {
 			// TrafficLogger requested to disconnect the client
-			_ = h.conn.CloseWithError(0, "")
+			_ = h.conn.CloseWithError(closeErrCodeTrafficLimitReached, "")
 			return
 		}
 	}