Improve MTU handling

- setting MTU on an interface updates the L3 max bytes too
- value cached in the adjacency is also updated
- MTU exceeded generates ICMP to sender

Change-Id: I343ec71d8e903b529594c4bd0543f04bc7f370b3
Signed-off-by: Neale Ranns <neale.ranns@cisco.com>

2 files changed, 36 insertions, 0 deletions

diff --git a/test/test_ip4.py b/test/test_ip4.py
index 79d4a36285c..1a611251eb5 100644
--- a/test/test_ip4.py
+++ b/test/test_ip4.py
@@ -1287,6 +1287,32 @@ class TestIPInput(VppTestCase):
         self.assertEqual(icmp.src, self.pg0.remote_ip4)
         self.assertEqual(icmp.dst, self.pg1.remote_ip4)
 
+        #
+        # MTU exceeded
+        #
+        p_mtu = (Ether(src=self.pg0.remote_mac,
+                       dst=self.pg0.local_mac) /
+                 IP(src=self.pg0.remote_ip4,
+                    dst=self.pg1.remote_ip4,
+                    ttl=10) /
+                 UDP(sport=1234, dport=1234) /
+                 Raw('\xa5' * 2000))
+
+        self.vapi.sw_interface_set_mtu(self.pg1.sw_if_index, 1500)
+
+        rx = self.send_and_expect(self.pg0, p_mtu * 65, self.pg0)
+        rx = rx[0]
+        icmp = rx[ICMP]
+
+        self.assertEqual(icmptypes[icmp.type], "dest-unreach")
+        self.assertEqual(icmpcodes[icmp.type][icmp.code],
+                         "fragmentation-needed")
+        self.assertEqual(icmp.src, self.pg0.remote_ip4)
+        self.assertEqual(icmp.dst, self.pg1.remote_ip4)
+
+        self.vapi.sw_interface_set_mtu(self.pg1.sw_if_index, 2500)
+        rx = self.send_and_expect(self.pg0, p_mtu * 65, self.pg1)
+
 
 if __name__ == '__main__':
     unittest.main(testRunner=VppTestRunner)
diff --git a/test/vpp_papi_provider.py b/test/vpp_papi_provider.py
index 15a566c5bc7..b7c76530307 100644
--- a/test/vpp_papi_provider.py
+++ b/test/vpp_papi_provider.py
@@ -629,6 +629,16 @@ class VppPapiProvider(object):
                         {'sw_if_index': sw_if_index,
                          'admin_up_down': admin_up_down})
 
+    def sw_interface_set_mtu(self, sw_if_index, mtu):
+        """
+        :param sw_if_index:
+        :param mtu:
+
+        """
+        return self.api(self.papi.sw_interface_set_mtu,
+                        {'sw_if_index': sw_if_index,
+                         'mtu': mtu})
+
     def create_subif(self, sw_if_index, sub_id, outer_vlan, inner_vlan,
                      no_tags=0, one_tag=0, two_tags=0, dot1ad=0, exact_match=0,
                      default_sub=0, outer_vlan_id_any=0, inner_vlan_id_any=0):