The DHCP client should enter the REBOOTING state when connecting to a

new network. If DHCP has bound to an address, it must be verified
after netif_set_link_up.

src/core/dhcp.c

@@ -100,6 +100,8 @@
 #define DHCP_MAX_MSG_LEN(netif)        (netif->mtu)
 #define DHCP_MAX_MSG_LEN_MIN_REQUIRED  576
 
+#define REBOOT_TRIES 2
+
 /* DHCP client state machine functions */
 static void dhcp_handle_ack(struct netif *netif);
 static void dhcp_handle_nak(struct netif *netif);
@@ -113,6 +115,7 @@ static void dhcp_bind(struct netif *netif);
 static err_t dhcp_decline(struct netif *netif);
 #endif /* DHCP_DOES_ARP_CHECK */
 static err_t dhcp_rebind(struct netif *netif);
+static err_t dhcp_reboot(struct netif *netif);
 static void dhcp_set_state(struct dhcp *dhcp, u8_t new_state);
 
 /* receive, unfold, parse and free incoming messages */
@@ -421,6 +424,12 @@ dhcp_timeout(struct netif *netif)
       dhcp_release(netif);
       dhcp_discover(netif);
     }
+  } else if (dhcp->state == DHCP_REBOOTING) {
+    if (dhcp->tries < REBOOT_TRIES) {
+      dhcp_reboot(netif);
+    } else {
+      dhcp_discover(netif);
+    }
   }
 }
 
@@ -705,6 +714,36 @@ dhcp_inform(struct netif *netif)
   netif->dhcp = old_dhcp;
 }
 
+/** Handle a possible change in the network configuration.
+ *
+ * This enters the REBOOTING state to verify that the currently bound
+ * address is still valid.
+ */
+void
+dhcp_network_changed(struct netif *netif)
+{
+  struct dhcp *dhcp = netif->dhcp;
+  if (!dhcp)
+    return;
+  switch (dhcp->state) {
+  case DHCP_REBINDING:
+  case DHCP_RENEWING:
+  case DHCP_BOUND:
+  case DHCP_REBOOTING:
+    netif_set_down(netif);
+    dhcp->tries = 0;
+    dhcp_reboot(netif);
+    break;
+  case DHCP_OFF:
+    /* stay off */
+    break;
+  default:
+    dhcp->tries = 0;
+    dhcp_discover(netif);
+    break;
+  }
+}
+
 #if DHCP_DOES_ARP_CHECK
 /**
  * Match an ARP reply with the offered IP address.
@@ -1054,6 +1093,53 @@ dhcp_rebind(struct netif *netif)
   return result;
 }
 
+/**
+ * Enter REBOOTING state to verify an existing lease
+ *
+ * @param netif network interface which must reboot
+ */
+static err_t
+dhcp_reboot(struct netif *netif)
+{
+  struct dhcp *dhcp = netif->dhcp;
+  err_t result;
+  u16_t msecs;
+  LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_reboot()\n"));
+  dhcp_set_state(dhcp, DHCP_REBOOTING);
+
+  /* create and initialize the DHCP message header */
+  result = dhcp_create_request(netif);
+  if (result == ERR_OK) {
+
+    dhcp_option(dhcp, DHCP_OPTION_MESSAGE_TYPE, DHCP_OPTION_MESSAGE_TYPE_LEN);
+    dhcp_option_byte(dhcp, DHCP_REQUEST);
+
+    dhcp_option(dhcp, DHCP_OPTION_MAX_MSG_SIZE, DHCP_OPTION_MAX_MSG_SIZE_LEN);
+    dhcp_option_short(dhcp, 576);
+
+    dhcp_option(dhcp, DHCP_OPTION_REQUESTED_IP, 4);
+    dhcp_option_long(dhcp, ntohl(dhcp->offered_ip_addr.addr));
+
+    dhcp_option_trailer(dhcp);
+
+    pbuf_realloc(dhcp->p_out, sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN + dhcp->options_out_len);
+
+    /* broadcast to server */
+    udp_connect(dhcp->pcb, IP_ADDR_ANY, DHCP_SERVER_PORT);
+    udp_sendto_if(dhcp->pcb, dhcp->p_out, IP_ADDR_BROADCAST, DHCP_SERVER_PORT, netif);
+    dhcp_delete_request(netif);
+    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_reboot: REBOOTING\n"));
+  } else {
+    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | 2, ("dhcp_reboot: could not allocate DHCP request\n"));
+  }
+  dhcp->tries++;
+  msecs = dhcp->tries < 10 ? dhcp->tries * 1000 : 10 * 1000;
+  dhcp->request_timeout = (msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS;
+  LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_reboot(): set request timeout %"U16_F" msecs\n", msecs));
+  return result;
+}
+
+
 /**
  * Release a DHCP lease.
  *

src/core/netif.c

@@ -55,6 +55,9 @@
 #if LWIP_AUTOIP
 #include "lwip/autoip.h"
 #endif /* LWIP_AUTOIP */
+#if LWIP_DHCP
+#include "lwip/dhcp.h"
+#endif /* LWIP_DHCP */
 
 #if LWIP_NETIF_STATUS_CALLBACK
 #define NETIF_STATUS_CALLBACK(n) { if (n->status_callback) (n->status_callback)(n); }
@@ -410,7 +413,13 @@ void netif_set_up(struct netif *netif)
       etharp_gratuitous(netif);
     }
 #endif /* LWIP_ARP */
-    
+
+#if LWIP_IGMP
+    /* resend IGMP memberships */
+    if (netif->flags & NETIF_FLAG_IGMP) {
+      igmp_report_groups( netif);
+    }
+#endif /* LWIP_IGMP */
   }
 }
 
@@ -463,6 +472,12 @@ void netif_set_link_up(struct netif *netif )
 {
   netif->flags |= NETIF_FLAG_LINK_UP;
 
+#if LWIP_DHCP
+  if (netif->dhcp) {
+    dhcp_network_changed(netif);
+  }
+#endif /* LWIP_DHCP */
+
 #if LWIP_AUTOIP
   if (netif->autoip) {
     autoip_network_changed(netif);

src/include/lwip/dhcp.h

@@ -124,6 +124,8 @@ err_t dhcp_release(struct netif *netif);
 void dhcp_stop(struct netif *netif);
 /** inform server of our manual IP address */
 void dhcp_inform(struct netif *netif);
+/** Handle a possible change in the network configuration */
+void dhcp_network_changed(struct netif *netif);
 
 /** if enabled, check whether the offered IP address is not in use, using ARP */
 #if DHCP_DOES_ARP_CHECK