diff --git a/bin/checksum_delta_diff_test.py b/bin/checksum_delta_diff_test.py
index 2ffb666..e86db98 100644
--- a/bin/checksum_delta_diff_test.py
+++ b/bin/checksum_delta_diff_test.py
@@ -149,9 +149,13 @@ if __name__ == '__main__':
 
     #    print("chk_t = {}".format(t))
 
-    e = Ether(src="02:53:55:42:45:01", dst='ff:ff:ff:ff:ff:ff')
-    i4 = IP(src = "192.168.1.1", dst = "192.168.4.2")
-    i6 = IPv6(src = "2001:db8:42::1", dst = "2001:db8::2")
+    e = Ether(src="00:00:0a:00:00:03", dst='00:00:0a:00:00:01')
+    i4 = IP(src = "10.0.0.1", dst = "10.1.1.1")
+    i6 = IPv6(src="2001:db8:1::a00:1", dst="2001:db8::1")
+
+#    e = Ether(src="02:53:55:42:45:01", dst='ff:ff:ff:ff:ff:ff')
+#    i4 = IP(src = "192.168.1.1", dst = "192.168.4.2")
+#    i6 = IPv6(src = "2001:db8:42::1", dst = "2001:db8::2")
     i62 = IPv6(src = "2001:db8:42::2", dst = "2001:db8::2")
     t = TCP(dport=80, sport=1337)
     u = UDP(dport=80, sport=1337)
diff --git a/bin/send_udp_packet_v4.py b/bin/send_udp_packet_v4.py
index 72f83fb..5ba2c7a 100644
--- a/bin/send_udp_packet_v4.py
+++ b/bin/send_udp_packet_v4.py
@@ -3,6 +3,8 @@
 import sys
 from scapy.all import *
 
+import checksum_from_scapy
+
 if __name__ == '__main__':
     iface = sys.argv[1]
 
@@ -25,5 +27,7 @@ if __name__ == '__main__':
     v6_rebuild = pkg_v6.__class__(str(pkg_v6))
     print("v6: {} - {}".format(v6_rebuild.__repr__(), v6_rebuild[UDP].chksum))
 
+    checksum_from_scapy.checksum()
+
 
     sendp(pkg, iface=iface, verbose=True)
diff --git a/p4src/checksum_diff.p4 b/p4src/checksum_diff.p4
index 8c626ad..5c2b72e 100644
--- a/p4src/checksum_diff.p4
+++ b/p4src/checksum_diff.p4
@@ -198,7 +198,7 @@ control MyIngress(inout headers hdr,
                     v6sum();
                     bit<16> diff = meta.v6sum - meta.v4sum;
                     # hdr.udp.checksum = hdr.udp.checksum + diff;
-                    hdr.udp.checksum = diff;
+                    hdr.udp.checksum = ~diff;
 
                     #else
                     meta.chk_udp_v6 = 1;