From 855d587243b84357c52b33e52eed407656f7a9c0 Mon Sep 17 00:00:00 2001
From: logicog <git@logicog.de>
Date: Fri, 13 Feb 2026 18:36:18 +0100
Subject: [PATCH] Add dhcpd VLAN parameter to restrict dhcpd to given VLAN

---
 cmd_parser.c     | 5 +++++
 dhcp.c           | 5 +++++
 html/system.html | 3 ++-
 html/system.js   | 7 ++++++-
 rtl837x_common.h | 2 ++
 uip/uip.c        | 8 ++++++--
 6 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/cmd_parser.c b/cmd_parser.c
index bb37703..953af4b 100644
--- a/cmd_parser.c
+++ b/cmd_parser.c
@@ -44,6 +44,7 @@ extern __xdata struct dhcp_state dhcp_state;
 __xdata uint8_t vlan_names[VLAN_NAMES_SIZE];
 __xdata uint16_t vlan_ptr;
 extern __xdata uint16_t management_vlan;
+extern __xdata uint16_t dhcpd_vlan;
 __xdata uint8_t gpio_last_value[8] = { 0 };
 
 // Temporatly for str to hex convertion value.
@@ -1001,6 +1002,10 @@ void cmd_parser(void) __banked
 			}
 		} else if (cmd_compare(0, "dhcpd")) {
 			if (cmd_words_b[1] > 0 && cmd_compare(1, "on")) {
+				if (cmd_words_b[2] > 0)
+					atoi_short(&dhcpd_vlan, cmd_words_b[2]);
+				else
+					dhcpd_vlan = 0;
 				dhcpd_start();
 			} else {
 				print_string("DHCP Server disabled\n");
diff --git a/dhcp.c b/dhcp.c
index 81a3d9d..6239593 100644
--- a/dhcp.c
+++ b/dhcp.c
@@ -89,6 +89,7 @@ struct dhcp_pkt {
 __xdata uint32_t long_value;
 __xdata struct dhcpd_cstate cstates[DHCPD_MAX_CLIENTS];
 __xdata uint8_t client_idx;
+__xdata uint16_t dhcpd_vlan;
 
 void dhcp_print_ip(uint8_t *a)
 {
@@ -558,6 +559,10 @@ void dhcpd_start(void) __banked
 		print_string("dhcpd_start failed to set up socket\n");
 		return;
 	}
+	if (!dhcpd_vlan)
+		print_string("dhcpd: enabling for all VLANs\n");
+	else
+		print_string("dhcpd: enabling for VLAN "); print_short(dhcpd_vlan); write_char('\n');
 	dhcp_state.state = DHCP_SERVER;
 
 	dhcp_state.server[1] = uip_hostaddr[0] >> 8; dhcp_state.server[0] = uip_hostaddr[0] & 0xff;
diff --git a/html/system.html b/html/system.html
index f950f7b..31b37c6 100644
--- a/html/system.html
+++ b/html/system.html
@@ -63,7 +63,8 @@
     When updating the above settings, remember to point your browser to the new IP afterwards:<br/>
     <input style="width:40%;" class="action" id="ip_sub" onclick="ipSub();" type="button" value="Update Settings"><br/>
     <br/><br/>
-    <label class="dhcpdon">Enable DHCP Server: <input id="dhcpd" type="checkbox"></label><br/>
+    <label class="dhcpdon">Enable DHCP Server: <input id="dhcpd" type="checkbox"></label><br/><br/>
+    <label class="dhcpdvlan">Limit DHCP Server to VLAN (0: serve all VLANs): <input type="number" min="0" max="2047" value="0" id="dhcpd_vid" name="dhcpd_vid"></label><br/>
     <input style="width:40%;" class="action" id="dhcpd_sub" onclick="dhcpdSub();" type="button" value="Change DHCPD State"><br/><br/><br/>
     Save all current settings to Flash:<br/>
     <input style="width:40%;" class="action" id="flash_sub" onclick="flashSave();" type="button" value="Save Settings to Flash">
diff --git a/html/system.js b/html/system.js
index ba1c74a..7f6dd1b 100644
--- a/html/system.js
+++ b/html/system.js
@@ -42,9 +42,14 @@ async function ipSub() {
 }
 async function dhcpdSub() {
   var dhcpd_cmd = "dhcpd off";
-  if (document.getElementById('dhcpd').checked)
+  if (document.getElementById('dhcpd').checked) {
     dhcpd_cmd = "dhcpd on";
+    var v=document.getElementById('dhcpd_vid').value
+    if (v && v!= 0)
+      dhcpd_cmd = dhcpd_cmd + " " + v;
+  }
   try {
+    console.log("Sending: ", dhcpd_cmd);
     const response = await fetch('/cmd', {
       method: 'POST',
       body: dhcpd_cmd
diff --git a/rtl837x_common.h b/rtl837x_common.h
index c69d303..f827149 100644
--- a/rtl837x_common.h
+++ b/rtl837x_common.h
@@ -97,6 +97,8 @@ struct flash_region_t {
 
 extern __xdata uint8_t uip_buf[UIP_CONF_BUFFER_SIZE+2];
 extern __xdata struct uip_eth_addr uip_ethaddr;
+extern __xdata uint16_t rx_packet_vlan;
+extern __xdata uint16_t dhcpd_vlan;
 
 // Headers for calls in the common code area (HOME/BANK0)
 void print_string(__code char *p);
diff --git a/uip/uip.c b/uip/uip.c
index 6f184db..55f960a 100644
--- a/uip/uip.c
+++ b/uip/uip.c
@@ -924,7 +924,7 @@ uip_process(u8_t flag) __banked
         UIP_STAT(++uip_stat.ip.drop);
         goto drop;
       }
-  }
+    }
 #else /* UIP_CONF_IPV6 */
     /* For IPv6, packet reception is a little trickier as we need to
        make sure that we listen to certain multicast addresses (all
@@ -938,7 +938,11 @@ uip_process(u8_t flag) __banked
     }
 #endif /* UIP_CONF_IPV6 */
   }
-
+  // If we serve only the designated DHCPD-VLAN, we drop the packet if not in that VLAN
+  if(BUF->proto == UIP_PROTO_UDP && dhcpd_vlan && UDPBUF->destport == HTONS(DHCP_SERVER_PORT) && dhcpd_vlan != rx_packet_vlan) {
+    UIP_STAT(++uip_stat.ip.drop);
+    goto drop;
+  }
 #if !UIP_CONF_IPV6
 //  if(uip_ipchksum() != 0xffff) { /* Compute and check the IP header
 //				    checksum. */