diff --git a/doc/plan.org b/doc/plan.org
index b1b2588..a0f05b2 100644
--- a/doc/plan.org
+++ b/doc/plan.org
@@ -5274,6 +5274,40 @@ Still using scapy + adjusted diff:
 gets
 
 sum 0xc5f2 (incorrect -> 0xe7cf)
+*** 2019-07-16: pcap for debugging tcp
+    pcap/tcp-udp-delta-2019-07-15-1454-h3.pcap
+    pcap/tcp-udp-delta-2019-07-15-1454-h1.pcap
+*** 2019-07-16: pcap for debugging udp
+    pcap/tcp-udp-delta-2019-07-16-0856-h3.pcap
+    pcap/tcp-udp-delta-2019-07-16-0856-h1.pcap
+*** 2019-07-16: testing with udp
+    - suspicion: missing some cases in tcp6
+
+#+BEGIN_CENTER
+p4@ubuntu:~$ mx h1 "echo V6-OK | socat - UDP6-LISTEN:2342"
+p4@ubuntu:~/master-thesis/bin$ mx h3 "echo V4-OK | socat - UDP:10.1.1.1:2342"
+#+END_CENTER
+
+08:57:19.998299 IP6 (hlim 64, next-header UDP (17) payload length: 14)
+2001:db8:1::a00:1.59997 > 2001:db8::1.2342: [bad udp cksum 0xd84c ->
+0xd84b!] UDP, length 6
+
+**** DONE Result: arp (partly?) missing?
+     CLOSED: [2019-07-16 Tue 11:00]
+
+**** TODO Result: udp checksum wrong
+     - should be: 0xd84b
+     - is: 0xd84c
+
+My code is +1 too high
+
+*** DONE 2019-07-16: understood scapy code
+    CLOSED: [2019-07-16 Tue 11:25]
+meta.v6sum = (bit<16>) ((((tmp>>8) & 0xff)|tmp<<8) & 0xffff) ;
+
+This is used to correct endianness!
+
+-> not needed in our case
 
 ** The NetPFGA saga
 Problems encountered:
diff --git a/p4app/wraptest.json b/p4app/wraptest.json
new file mode 100644
index 0000000..1e1ef16
--- /dev/null
+++ b/p4app/wraptest.json
@@ -0,0 +1,48 @@
+{
+  "program": "../p4src/wraptest.p4",
+  "switch": "simple_switch",
+  "compiler": "p4c",
+  "options": "--target bmv2 --arch v1model --std p4-16",
+  "switch_cli": "simple_switch_CLI",
+  "cli": true,
+  "pcap_dump": true,
+  "enable_log": true,
+  "topo_module": {
+    "file_path": "",
+    "module_name": "p4utils.mininetlib.apptopo",
+    "object_name": "AppTopoStrategies"
+  },
+  "controller_module": null,
+  "topodb_module": {
+    "file_path": "",
+    "module_name": "p4utils.utils.topology",
+    "object_name": "Topology"
+  },
+  "mininet_module": {
+    "file_path": "",
+    "module_name": "p4utils.mininetlib.p4net",
+    "object_name": "P4Mininet"
+  },
+    "topology": {
+        "assignment_strategy": "l2",
+        "auto_arp_tables": false,
+        "links": [["h1", "s1"], ["h2", "s1"], ["h3", "s1"], ["h4","s1"]],
+        "hosts": {
+            "h1": {
+            },
+            "h2": {
+            }
+            ,
+            "h3": {
+            }
+            ,
+            "h4": {
+            }
+        },
+        "switches": {
+            "s1": {
+	            "cpu_port" : true
+            }
+        }
+    }
+}
diff --git a/p4src/actions_delta_checksum.p4 b/p4src/actions_delta_checksum.p4
index 0a48541..0697360 100644
--- a/p4src/actions_delta_checksum.p4
+++ b/p4src/actions_delta_checksum.p4
@@ -52,7 +52,7 @@ action v6sum() {
     tmp = (tmp >> 16) + (tmp & 0xffff);
 //    tmp = tmp + (tmp >> 16);
     tmp = ~tmp;
-//    meta.v6sum = (bit<16>) ((((tmp>>8) & 0xff)|tmp<<8) & 0xffff) ;
+
     meta.v6sum = (bit<16>) tmp;
 }
 
diff --git a/p4src/wraptest.p4 b/p4src/wraptest.p4
new file mode 100644
index 0000000..3508cef
--- /dev/null
+++ b/p4src/wraptest.p4
@@ -0,0 +1,50 @@
+/* -*- P4_16 -*- */
+#include <core.p4>
+#include <v1model.p4>
+
+#include "headers.p4"
+#include "parsers.p4"
+
+control MyIngress(inout headers hdr,
+    inout metadata meta,
+    inout standard_metadata_t standard_metadata) {
+
+	/********************** APPLYING TABLES ***********************************/
+    apply {
+        if(hdr.tcp.isValid()) {
+            /* test wrap around */
+            hdr.tcp.checksum = 0xffff;
+            hdr.tcp.checksum = checksum + 2;
+        }
+        standard_metadata.egress_spec = 1;
+    }
+}
+
+control MyEgress(inout headers hdr,
+                 inout metadata meta,
+                 inout standard_metadata_t standard_metadata) {
+	apply {
+	}
+}
+
+control MyVerifyChecksum(inout headers hdr, inout metadata meta) {
+    apply {}
+}
+
+
+control MyComputeChecksum(inout headers  hdr, inout metadata meta) {
+    apply {}
+}
+
+/*************************************************************************
+***********************  S W I T C H  *******************************
+*************************************************************************/
+
+V1Switch(
+    MyParser(),
+    MyVerifyChecksum(),
+    MyIngress(),
+    MyEgress(),
+    MyComputeChecksum(),
+    MyDeparser()
+) main;
\ No newline at end of file