diff --git a/ryu/app/rest_router.py b/ryu/app/rest_router.py
index 30812a7..100d565 100644
--- a/ryu/app/rest_router.py
+++ b/ryu/app/rest_router.py
@@ -1523,18 +1523,37 @@ class OfCtl(object):
         eth = protocol_list[ETHERNET]
         e = ethernet.ethernet(eth.src, eth.dst, ether_proto)
 
+        ip = protocol_list[IPV4]
+
         if icmp_data is None and msg_data is not None:
-            ip_datagram = msg_data[offset:]
+            # RFC 4884 says that we should send "at least 128 octets"
+            # if we are using the ICMP Extension Structure.
+            # We're not using the extension structure, but let's send
+            # up to 128 bytes of the original msg_data.
+            #
+            # RFC 4884 also states that the length field is interpreted in
+            # 32 bit units, so the length calculated in bytes needs to first
+            # be divided by 4, then increased by 1 if the modulus is non-zero.
+            #
+            # Finally, RFC 4884 says, if we're specifying the length, we MUST
+            # zero pad to the next 32 bit boundary.
+            end_of_data = offset + len(ip) + 128
+            ip_datagram = bytearray()
+            ip_datagram += msg_data[offset:end_of_data]
+            data_len = int(len(ip_datagram) / 4)
+            length_modulus = int(len(ip_datagram) % 4)
+            if length_modulus:
+                data_len += 1
+                ip_datagram += bytearray([0] * (4 - length_modulus))
             if icmp_type == icmp.ICMP_DEST_UNREACH:
-                icmp_data = icmp.dest_unreach(data_len=len(ip_datagram),
+                icmp_data = icmp.dest_unreach(data_len=data_len,
                                               data=ip_datagram)
             elif icmp_type == icmp.ICMP_TIME_EXCEEDED:
-                icmp_data = icmp.TimeExceeded(data_len=len(ip_datagram),
+                icmp_data = icmp.TimeExceeded(data_len=data_len,
                                               data=ip_datagram)
 
         ic = icmp.icmp(icmp_type, icmp_code, csum, data=icmp_data)
 
-        ip = protocol_list[IPV4]
         if src_ip is None:
             src_ip = ip.dst
         ip_total_length = ip.header_length * 4 + ic._MIN_LEN