diff --git a/src/core/dns.c b/src/core/dns.c
index 21170cf4..334653fe 100644
--- a/src/core/dns.c
+++ b/src/core/dns.c
@@ -114,7 +114,7 @@ static u16_t dns_txid;
 /** DNS server IP address */
 #ifndef DNS_SERVER_ADDRESS
 #if LWIP_IPV4
-#define DNS_SERVER_ADDRESS(ipaddr)        ip_addr_set_ip4_u32(ipaddr, ipaddr_addr("208.67.222.222")) /* resolver1.opendns.com */
+#define DNS_SERVER_ADDRESS(ipaddr)        ip_addr_set_ip4_u32(ipaddr, 0)//ipaddr_addr("208.67.222.222")) /* resolver1.opendns.com */
 #else
 #define DNS_SERVER_ADDRESS(ipaddr)        ipaddr_aton("2001:4860:4860::8888", ipaddr)
 #endif
@@ -283,6 +283,7 @@ static void dns_init_local(void);
 /* forward declarations */
 static void dns_recv(void *s, struct udp_pcb *pcb, struct pbuf *p, const ip_addr_t *addr, u16_t port);
 static void dns_check_entries(void);
+static void dns_call_found(u8_t idx, ip_addr_t* addr);
 
 /*-----------------------------------------------------------------------------
  * Globals
@@ -673,11 +674,11 @@ dns_parse_name(struct pbuf* p, u16_t query_idx)
 /**
  * Send a DNS query packet.
  *
- * @param entry the DNS table entry for which to send a request
+ * @param idx the DNS table entry index for which to send a request
  * @return ERR_OK if packet is sent; an err_t indicating the problem otherwise
  */
 static err_t
-dns_send(struct dns_table_entry* entry)
+dns_send(u8_t idx)
 {
   err_t err;
   struct dns_hdr hdr;
@@ -687,11 +688,19 @@ dns_send(struct dns_table_entry* entry)
   const char *hostname, *hostname_part;
   u8_t n;
   u8_t pcb_idx;
+  struct dns_table_entry* entry = &dns_table[idx];
 
   LWIP_DEBUGF(DNS_DEBUG, ("dns_send: dns_servers[%"U16_F"] \"%s\": request\n",
               (u16_t)(entry->server_idx), entry->name));
   LWIP_ASSERT("dns server out of array", entry->server_idx < DNS_MAX_SERVERS);
-  LWIP_ASSERT("dns server has no IP address set", !ip_addr_isany(&dns_servers[entry->server_idx]));
+  if (ip_addr_isany(&dns_servers[entry->server_idx])) {
+    /* DNS server not valid anymore, e.g. PPP netif has been shut down */
+    /* call specified callback function if provided */
+    dns_call_found(idx, NULL);
+    /* flush this entry */
+    entry->state = DNS_STATE_UNUSED; 
+    return ERR_OK;
+  }
 
   /* if here, we have either a new query or a retry on a previous query to process */
   p = pbuf_alloc(PBUF_TRANSPORT, (u16_t)(SIZEOF_DNS_HDR + strlen(entry->name) + 2 +
@@ -835,7 +844,7 @@ dns_call_found(u8_t idx, ip_addr_t* addr)
     if (dns_requests[i].found && (dns_requests[i].dns_table_idx == idx)) {
       (*dns_requests[i].found)(dns_table[idx].name, addr, dns_requests[i].arg);
       /* flush this entry */
-      dns_requests[i].found   = NULL;
+      dns_requests[i].found = NULL;
     }
   }
 #else
@@ -919,7 +928,7 @@ dns_check_entry(u8_t i)
       entry->retries = 0;
 
       /* send DNS packet for this entry */
-      err = dns_send(entry);
+      err = dns_send(i);
       if (err != ERR_OK) {
         LWIP_DEBUGF(DNS_DEBUG | LWIP_DBG_LEVEL_WARNING,
                     ("dns_send returned error: %s\n", lwip_strerr(err)));
@@ -950,7 +959,7 @@ dns_check_entry(u8_t i)
         entry->tmr = entry->retries;
 
         /* send DNS packet for this entry */
-        err = dns_send(entry);
+        err = dns_send(i);
         if (err != ERR_OK) {
           LWIP_DEBUGF(DNS_DEBUG | LWIP_DBG_LEVEL_WARNING,
                       ("dns_send returned error: %s\n", lwip_strerr(err)));