From c82f04f54c1ad178a810397c79efdb8e5238c3bf Mon Sep 17 00:00:00 2001
From: Simon Goldschmidt <goldsimon@gmx.de>
Date: Thu, 27 Feb 2014 22:44:16 +0100
Subject: [PATCH] fixed bug #40303 DHCP xid renewed when sending a DHCPREQUEST

---
 CHANGELOG       |  3 +++
 src/core/dhcp.c | 13 ++++++++-----
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/CHANGELOG b/CHANGELOG
index a8b95e80..61c5862a 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -96,6 +96,9 @@ HISTORY
 
  ++ Bugfixes:
 
+  2014-02-27: Simon Goldschmidt
+  * dhcp.c: fixed bug #40303 DHCP xid renewed when sending a DHCPREQUEST
+
   2014-02-27: Simon Goldschmidt
   * raw.c: fixed bug #41680 raw socket can not receive IPv6 packet when
     IP_SOF_BROADCAST_RECV==1
diff --git a/src/core/dhcp.c b/src/core/dhcp.c
index 21fd7845..4c605212 100644
--- a/src/core/dhcp.c
+++ b/src/core/dhcp.c
@@ -1671,15 +1671,18 @@ dhcp_create_msg(struct netif *netif, struct dhcp *dhcp, u8_t message_type)
   LWIP_ASSERT("dhcp_create_msg: check that first pbuf can hold struct dhcp_msg",
            (dhcp->p_out->len >= sizeof(struct dhcp_msg)));
 
-  /* reuse transaction identifier in retransmissions */
-  if (dhcp->tries == 0) {
+  /* DHCP_REQUEST should reuse 'xid' from DHCPOFFER */
+  if (message_type != DHCP_REQUEST) {
+    /* reuse transaction identifier in retransmissions */
+    if (dhcp->tries == 0) {
 #if DHCP_CREATE_RAND_XID && defined(LWIP_RAND)
-    xid = LWIP_RAND();
+      xid = LWIP_RAND();
 #else /* DHCP_CREATE_RAND_XID && defined(LWIP_RAND) */
-    xid++;
+      xid++;
 #endif /* DHCP_CREATE_RAND_XID && defined(LWIP_RAND) */
+    }
+    dhcp->xid = xid;
   }
-  dhcp->xid = xid;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
               ("transaction id xid(%"X32_F")\n", xid));