From e9171d7d228a456dd1dd5a1e67109b05b75f4e5b Mon Sep 17 00:00:00 2001
From: logicog <git@logicog.de>
Date: Wed, 7 Jan 2026 11:32:47 +0100
Subject: [PATCH] Handle outgoing DHCP server messages correctly

---
 uip/uip_arp.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/uip/uip_arp.c b/uip/uip_arp.c
index 362b1b8..90fe6e9 100644
--- a/uip/uip_arp.c
+++ b/uip/uip_arp.c
@@ -106,6 +106,7 @@ struct ethip_hdr {
   u16_t ipchksum;
   u16_t srcipaddr[2],
     destipaddr[2];
+  u16_t sport, dport;
 };
 
 #define ARP_REQUEST 1
@@ -370,6 +371,11 @@ uip_arp_out(void) __banked
      If not ARP table entry is found, we overwrite the original IP
      packet with an ARP request for the IP address. */
 
+  if (IPBUF->sport == 0x4300 && !IPBUF->destipaddr[0] && !IPBUF->destipaddr[1]) {
+    IPBUF->destipaddr[0] = 0xffff;
+    IPBUF->destipaddr[1] = 0xffff;
+    IPBUF->dport = 0x4400;
+  }
   /* First check if destination is a local broadcast. */
   if(uip_ipaddr_cmpc(IPBUF->destipaddr, broadcast_ipaddr)) {
     memcpyc(IPBUF->ethhdr.dest.addr, broadcast_ethaddr.addr, 6);