diff --git a/Makefile b/Makefile
index e88202b..df405df 100644
--- a/Makefile
+++ b/Makefile
@@ -10,7 +10,7 @@ SUBDIRSCLEAN=$(addsuffix clean,$(SUBDIRS))
 
 all: $(SUBDIRS) rtlplayground.bin
 
-SRCS = rtlplayground.c rtl837x_flash.c rtl837x_phy.c rtl837x_port.c cmd_parser.c html_data.c rtl837x_igmp.c
+SRCS = rtlplayground.c rtl837x_flash.c rtl837x_phy.c rtl837x_port.c cmd_parser.c html_data.c rtl837x_igmp.c rtl837x_stp.c
 OBJS = ${SRCS:.c=.rel}
 OBJS += uip/timer.rel uip/uip-fw.rel uip/uip-neighbor.rel uip/uip-split.rel uip/uip.rel uip/uip_arp.rel uip/uiplib.rel httpd/httpd.rel httpd/page_impl.rel
 
diff --git a/rtl837x_regs.h b/rtl837x_regs.h
index 23705fa..a07f2be 100644
--- a/rtl837x_regs.h
+++ b/rtl837x_regs.h
@@ -145,6 +145,14 @@
 #define RTL837X_IGMP_PORT_CFG		0x52a0
 #define RTL837X_MC_FLOODMASK		0x5368
 
+/*
+ * Loop detection / STP
+ */
+
+#define RTL8373_RLDP_TIMER		0x1074
+#define RTL837X_RMA0_CONF		0x4ecc
+#define RTL837X_RMA_CONF		0x4f1c
+
 
 #ifdef REGDBG
 
diff --git a/rtl837x_stp.c b/rtl837x_stp.c
new file mode 100644
index 0000000..06144b0
--- /dev/null
+++ b/rtl837x_stp.c
@@ -0,0 +1,98 @@
+/*
+ * This is a driver implementation for the Spanning Tree Protocol features for the RTL837x platform
+ * This code is in the Public Domain
+ */
+
+// #define REGDBG
+// #define DEBUG
+
+#include <stdint.h>
+#include "rtl837x_common.h"
+#include "rtl837x_sfr.h"
+#include "rtl837x_regs.h"
+#include "rtl837x_igmp.h"
+#include "uip.h"
+
+extern __xdata uint8_t minPort;
+extern __xdata uint8_t maxPort;
+extern __xdata uint8_t nSFPPorts;
+extern __xdata uint8_t cpuPort;
+extern __xdata uint8_t isRTL8373;
+
+extern __code struct uip_eth_addr uip_ethaddr;
+
+extern __xdata uint8_t uip_buf[UIP_CONF_BUFFER_SIZE+2];
+
+// 8899 04 0000 20 0004
+struct rtl_tag {
+	uint16_t tag;
+	uint8_t version;
+	uint16_t dummy;
+	uint8_t flag;
+	uint16_t pmask;
+};
+
+
+struct stp_pkt {
+	uint8_t stp_addr[6];
+	uint8_t src_addr[6];
+	struct rtl_tag rtl_tag;
+	uint16_t msg_len;
+	uint8_t dsap;
+	uint8_t ssap;
+	uint8_t ctrl;
+	uint16_t proto;
+	uint8_t version;
+	uint8_t root_prio;
+	uint8_t root_ext;
+	uint8_t root_mac[8];
+	uint8_t bridge_prio;
+	uint8_t bridge_ext;
+	uint8_t bridge_mac[8];
+	uint8_t port_prio;
+	uint8_t port_id;
+	uint16_t age;
+	uint16_t age_max;
+	uint16_t fwd_delay;
+};
+
+
+#define STP_O ((__xdata struct stp_pkt *)&uip_buf[RTL_TAG_SIZE + VLAN_TAG_SIZE])
+
+void stp_cnf_send(uint8_t port) __banked
+{
+	STP_O->stp_addr[0] = 0x01; STP_O->stp_addr[1] = 0x80; STP_O->stp_addr[2] = 0xc2;
+	STP_O->stp_addr[3] = STP_O->stp_addr[4] = STP_O->stp_addr[5] = 0x00;
+
+	STP_O->rtl_tag.tag = HTONS(0x8899);
+	STP_O->rtl_tag.version = 0x04;
+	STP_O->rtl_tag.dummy = 0x0000;
+	STP_O->rtl_tag.flag = 0x20; // WHY ???
+	STP_O->rtl_tag.pmask = HTONS(((uint16_t)1) << port);
+
+	STP_O->msg_len = HTONS(0x27);
+	STP_O->dsap = 0x42;
+	STP_O->ssap = 0x42;
+	STP_O->ctrl = 0x03;
+	STP_O->proto = 0x0000;
+	STP_O->version = 0;
+
+	memcpyc(STP_O->src_addr, uip_ethaddr.addr, 6);
+	memcpyc(STP_O->root_mac, uip_ethaddr.addr, 6); // For now we are the root-bridge
+	memcpyc(STP_O->bridge_mac, uip_ethaddr.addr, 6);
+
+	STP_O->root_prio = 0x80;
+	STP_O->root_ext = 0x00;
+
+	STP_O->bridge_prio = 0x80;
+	STP_O->bridge_ext = 0x00;
+
+	STP_O->port_prio = 0x80;
+	STP_O->port_id = port;
+	STP_O->age = 0x00;
+	STP_O->age_max = 0x20;
+	STP_O->fwd_delay = 0x0f;
+
+
+	uip_len = 0x27 + sizeof(struct rtl_tag);
+}
diff --git a/rtl837x_stp.h b/rtl837x_stp.h
new file mode 100644
index 0000000..9fd2f7b
--- /dev/null
+++ b/rtl837x_stp.h
@@ -0,0 +1,7 @@
+#ifndef _RTL837X_STP_H_
+#define _RTL837X_STP_H_
+
+#include <stdint.h>
+void stp_cnf_send(uint8_t port) __banked;
+
+#endif