Index: libnetutil/netutil.cc
===================================================================
--- libnetutil/netutil.cc	(revision 34054)
+++ libnetutil/netutil.cc	(working copy)
@@ -3960,6 +3960,11 @@
   } *NCC = NULL;
   static int NCCsz = 0;
   static int NCCcapacity = 0;
+  static struct NameNotFoundCache {
+    char dnetd[64];
+  } *NNFC = NULL;
+  static int NNFCsz = 0;
+  static int NNFCcapacity = 0;
   int i;
   char tmpdev[128];
 
@@ -3971,6 +3976,13 @@
                                                     sizeof(*NCC));
     NCCsz = 0;
   }
+  if (!NNFC) {
+    NNFCcapacity = 5;
+    NNFC =
+        (struct NameNotFoundCache *) safe_zalloc(NNFCcapacity *
+                                                    sizeof(*NNFC));
+    NNFCsz = 0;
+  }
   // First check if the name is already in the cache
   for (i = 0; i < NCCsz; i++) {
     if (strcmp(NCC[i].dnetd, dnetdev) == 0) {
@@ -3978,12 +3990,28 @@
       return 1;
     }
   }
-
+  // Check if the name is already in the name not found cache
+  for (i = 0; i < NNFCsz; i++) {
+    if (strcmp(NNFC[i].dnetd, dnetdev) == 0) {
+      return 0;
+    }
+  }
   // OK, so it isn't in the cache.  Let's ask dnet for it.
-/* Converts a dnet interface name (ifname) to its pcap equivalent, which is stored in
-pcapdev (up to a length of pcapdevlen).  Returns 0 and fills in pcapdev if successful. */
-  if (eth_get_pcap_devname(dnetdev, tmpdev, sizeof(tmpdev)) != 0)
-    return 0;
+  /* Converts a dnet interface name (ifname) to its pcap equivalent, which is stored in
+  pcapdev (up to a length of pcapdevlen).  Returns 1 and fills in pcapdev if successful. */
+  if (eth_get_pcap_devname(dnetdev, tmpdev, sizeof(tmpdev)) != 0) {
+      // We've got it.  Let's add it to the not found cache
+      if (NNFCsz >= NNFCcapacity) {
+        NNFCcapacity <<= 2;
+        NNFC =
+            (struct NameNotFoundCache *) safe_realloc(NNFC,
+                                                         NNFCcapacity *
+                                                         sizeof(*NNFC));
+      }
+      Strncpy(NNFC[NNFCsz].dnetd, dnetdev, sizeof(NNFC[0].dnetd));
+      NNFCsz++;
+      return 0;
+  }
 
   // We've got it.  Let's add it to the cache
   if (NCCsz >= NCCcapacity) {