diff --git a/cmd_parser.c b/cmd_parser.c
index 45308ba..b25a996 100644
--- a/cmd_parser.c
+++ b/cmd_parser.c
@@ -791,6 +791,9 @@ void parse_sfp(void)
 	} else if (cmd_compare(2, "1g")) {
 		print_string(" 1G\n");
 		sfp_speed[slot] = SFP_SPEED_1G;
+	} else if (cmd_compare(2, "100m")) {
+		print_string(" 100M\n");
+		sfp_speed[slot] = SFP_SPEED_100M;
 	} else if (cmd_compare(2, "auto")) {
 		print_string(" AUTO\n");
 		sfp_speed[slot] = SFP_SPEED_AUTO;
diff --git a/rtl837x_common.h b/rtl837x_common.h
index 3be8c7f..6d6abb5 100644
--- a/rtl837x_common.h
+++ b/rtl837x_common.h
@@ -94,6 +94,7 @@ struct vlan_tag {
 
 enum sfp_speeds {
 	SFP_SPEED_AUTO = 0,
+	SFP_SPEED_100M,
 	SFP_SPEED_1G,
 	SFP_SPEED_2G5,
 	SFP_SPEED_5G,
diff --git a/rtl837x_regs.h b/rtl837x_regs.h
index c1a27bb..f5bd951 100644
--- a/rtl837x_regs.h
+++ b/rtl837x_regs.h
@@ -73,6 +73,7 @@
  */
 #define SDS_SGMII		0x02
 #define SDS_1000BX_FIBER	0x04
+#define SDS_100FX		0x05
 #define SDS_QXGMII		0x0d
 #define SDS_HISGMII		0x12
 #define SDS_HSG			0x16
diff --git a/rtlplayground.c b/rtlplayground.c
index 7499f45..6b56db3 100644
--- a/rtlplayground.c
+++ b/rtlplayground.c
@@ -927,6 +927,10 @@ void sds_config(uint8_t sds, uint8_t mode)
 		v = 0x0200;
 		page = 0x2e;
 		break;
+	case SDS_100FX:
+		v = 0x0200;
+		page = 0x26;
+		break;
 	default:
 		print_string("Error in SDS Mode\n");
 		return;
@@ -1170,6 +1174,8 @@ void handle_tx(void)
 
 static inline uint8_t sfp_rate_to_sds_config(register uint8_t rate)
 {
+	if (rate == 0x1 || rate == 0x2)
+		return SDS_100FX;
 	if (rate == 0xc || rate == 0xd)
 		return SDS_1000BX_FIBER;
 	if (rate >= 0x19 && rate <= 0x20)  // Ethernet 2.5 GBit
@@ -1235,7 +1241,9 @@ void handle_sfp(void)
 				// Read Reg 12: Signalling rate (including overhead) in 100Mbit: 0xd: 1Gbit, 0x67:10Gbit
 				delay(100); // Delay, because some modules need time to wake up
 				uint8_t rate = sfp_read_reg(sfp, 12);
-				if (sfp_speed[sfp] == SFP_SPEED_1G)
+				if (sfp_speed[sfp] == SFP_SPEED_100M)
+					rate = 0x1;
+				else if (sfp_speed[sfp] == SFP_SPEED_1G)
 					rate = 0xc;
 				else if (sfp_speed[sfp] == SFP_SPEED_2G5)
 					rate = 0x19;