DSMO invalid netmask fix

PiperOrigin-RevId: 827987592

Author: Capirca Team

capirca/lib/summarizer.py

@@ -261,11 +261,14 @@ def _SummarizeSameMask(nets):
         # or they are "a pair".
         if (current_net.netmask == pair_net.netmask and
             (xored_address & (xored_address - 1) == 0) and xored_address > 0):
+          new_netmask = current_net.netmask ^ xored_address
+          if new_netmask.bit_length() not in (0, 32):
+            singletons.append(current_net)
+            break
           # if pair was found, remove both, add paired up network
           # to combinetons for next run and move along
           # otherwise this network can never be paired
           current_nets.pop(pair_net_index)
-          new_netmask = current_net.netmask ^ xored_address
           # summarize supplied networks into one using discontinuous
           # subnet mask.
           combinetons.append(DSMNet(min(current_net.address, pair_net.address),

tests/lib/summarizer_test.py

@@ -85,6 +85,16 @@ def testSummarizeNoNetworks(self):
     result = summarizer.Summarize(nets)
     self.assertEqual(len(result), 256)
 
+  def testDontSummarizeWeirdMasks(self):
+    nets = [
+        # combining these results in a weird netmask, dont do it
+        nacaddr.IPv4('34.144.128.0/19'),
+        nacaddr.IPv4('162.144.128.0/19'),
+    ]
+    result = summarizer.Summarize(nets)
+    self.assertEqual(result, [summarizer.DSMNet(579895296, 4294959104),
+                              summarizer.DSMNet(2727378944, 4294959104)])
+
   def testSummarizeSomeNetworks(self):
     nets = [
         # continiously summarizable to one /25