---
title: "WIZ550S2E TCP not working on corporate network. loses first 16 bytes of data."
url: "https://maker.wiznet.io/forum/14552"
markdown_url: "https://maker.wiznet.io/forum/14552/md"
type: "Forum topic"
category: "Serial-to-Ethernet & ConfigTool"
author: "jcomfort"
created: "2022-05-12T16:42:33+09:00"
last_activity: "2022-08-11T08:36:12+09:00"
language: "en"
views: 391
replies: 4
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# WIZ550S2E TCP not working on corporate network. loses first 16 bytes of data.

## Question

Asked by jcomfort on 2022-05-12 in Serial-to-Ethernet & ConfigTool.

Hi, I am new to the forum, but have been working with the WIZ550S2E with version 1.4.0 firmware for a few months.
I am using the module in 2 application in different modes, both use DHCP.
Mode #1 UDP in Data Mode
Mode #2 TCP in Command mode, using AT+NSEND

On small networks both modes work fine. On a corporate (domain) network with a Windows DHCP server Mode #1 works fine but in Mode #2 I am losing the 1st 16 bytes of the data packet. This Wireshark trace shows the problem:

[![image](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/b/bbbb7260a8d055dac6b10910a8bdd4981650e82b.png) image1190×667 59.2 KB](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/b/bbbb7260a8d055dac6b10910a8bdd4981650e82b.png)

This trace shows what should be in the data block:

[![image](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/6/6011b725a3f052cf251430e37aaf343c8e46dd75.jpeg) image1454×815 162 KB](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/6/6011b725a3f052cf251430e37aaf343c8e46dd75.jpeg)

Does anyone have any suggestions as to what is causing this data loss?

Thanks

John

## Replies

### Reply 1 by jcomfort, 2022-08-09

A follow on to this earlier post. Command mode UDP messages have the same problem. OK in data mode, but when sending on a corporate network we again lose the first 16 or 17 bytes in UDP using AT+NSEND

any suggestions?

thanks

John

### Reply 2 by austin, 2022-08-11

Hi John,

Could you share the ‘*.pacp’ file that captures the problem?

### Reply 3 by jcomfort, 2022-08-11 (in reply to reply 2)

Hi Austin,

I have attached the filtered file (tcp.port==4437) to keep it small!

Hope this is of use

Best regards

John

John Comfort

JCA Systems Ltd

(Attachment EC4Plus_LAN_BATH6 filtered.pcapng is missing)

### Reply 4 by jcomfort, 2022-08-11 (in reply to reply 2)

Hi Austin,

I have attached the filtered file (tcp.port==4437) to keep it small!

Hope this is of use

Best regards

John

John Comfort

JCA Systems Ltd

[EC4Plus_LAN_BATH6 filtered.zip](https://maker.wiznet.io/forum/legacyFile.asp?path=yvsMLrldRw9X2BhvB8rhQWMTJ18.zip) (15.5 KB)

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Source: https://maker.wiznet.io/forum/14552