--- title: "TCP Does not connect on NLB Unicast Server" url: "https://maker.wiznet.io/forum/12777" markdown_url: "https://maker.wiznet.io/forum/12777/md" type: "Forum topic" category: "Serial-to-Ethernet & ConfigTool" author: "gstef" created: "2018-03-01T13:18:37+09:00" last_activity: "2018-03-09T00:35:13+09:00" language: "en" views: 1589 replies: 8 source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)" --- # TCP Does not connect on NLB Unicast Server ## Question Asked by gstef on 2018-03-01 in Serial-to-Ethernet & ConfigTool. Hi, i have a problem with WIZ750SR, the module is connecting on a network 192.168.0.0/24, in this network there was a server with a Network Load Balancing service in “unicast” mode. when i try to connect from the server to the module this not work. if i connect with other pc on the network work well. what is the problem? can i setup module to communicate? thanks in advance ## Replies ### Reply 1 by irina, 2018-03-06 ![](https://avatars.discourse-cdn.com/v4/letter/g/53a042/48.png) gstef: > the module is connecting on a network 192.168.0.0/24, in this network there was a server with a Network Load Balancing service in “unicast” mode. > > when i try to connect from the server to the module this not work. We are going to test it in a similar environment to your network. Can you tell me more about your Network configurations? If possible, please save and attach [wireshark](https://www.wireshark.org/download.html) packet capture (.pcapng) on this post when the WIZ750SR module is trying to connect to the server with NLB. Regards, Eric ### Reply 2 by gstef, 2018-03-06 (in reply to reply 1) thank you for replying, the issue is simple, probably need to use an arp table to resolve it. ``` create a server (windows server 2008 or newer), put fixed ip at ``` the network (ex.192.168.0.100), install features:network load balancing, with NLB manager wizard create a NLB with the Host IP as guest (ex.192.168.0.100) and the NLB in the same subnet (ex:192.168.0.101). now try to ping or connect to any pc or router and this work whe try to connecto with WIZ750SR not respond at all ``` the issue is caused by NLB that in the request header put a ``` different mac address (not the correct ones) and thew module will respond at this mac address. [![](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/1/1fb37a78dc5624bf926c6109be044b081ed8e29f.jpg) 700×66 7.6 KB](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/1/1fb37a78dc5624bf926c6109be044b081ed8e29f.jpg) ![](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/4/43cb5034a788d9ca422f3b84b96b569b59118bab.png) ![](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/b/bfde8fab40b562da87255c901cdff0fd84482681.gif) ![](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/3/3da5f28a9e3838af7e188c1f2a59fab0d1f30003.png) ![](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/1/17adbcd185931973a26842c98f8231526a35f8c8.gif) ### Reply 3 by gstef, 2018-03-06 (in reply to reply 1) thank you for replying, the issue is simple, probably need to use an arp table to resolve it. ``` create a server (windows server 2008 or newer), put fixed ip at ``` the network (ex.192.168.0.100), install features:network load balancing, with NLB manager wizard create a NLB with the Host IP as guest (ex.192.168.0.100) and the NLB in the same subnet (ex:192.168.0.101) in unicast mode. now try to ping or connect to any pc or router and this work whe try to connecto with WIZ750SR not respond at all ``` the issue is caused by NLB that in the request header put a ``` different mac address (not the correct ones) and thew module will respond at this mac address. [![](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/1/1fb37a78dc5624bf926c6109be044b081ed8e29f.jpg) 700×66 7.6 KB](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/1/1fb37a78dc5624bf926c6109be044b081ed8e29f.jpg) ![](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/4/43cb5034a788d9ca422f3b84b96b569b59118bab.png) ![](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/b/bfde8fab40b562da87255c901cdff0fd84482681.gif) ![](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/3/3da5f28a9e3838af7e188c1f2a59fab0d1f30003.png) ![](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/1/17adbcd185931973a26842c98f8231526a35f8c8.gif) ### Reply 4 by bangbh, 2018-03-07 Hi gstef! I am Peter. I tested MS NLB with WIZ750SR. But I could not find the any problem that you mentioned. You can see the test environment in the following picture. Server: windows server 2008 R2 NLB unicast [![NLB%20test](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/c/c42ac3f20a43f1ccfd2225d1a33a41d4f46fdeb4.png) NLB%20test1148×591 61.2 KB](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/c/c42ac3f20a43f1ccfd2225d1a33a41d4f46fdeb4.png) And I also tested that the NLB function works well. After configuring the NLB cluster, I turned off the server 1 and I checked that the WIZ750SR was connected to the server 2. It worked well too. You can see the result in the following picture. [![nlb%20wireshark](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/d/d768f1caf91e18dfbbdf997f5b531a2126a73a16.png) nlb%20wireshark1303×800 830 KB](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/d/d768f1caf91e18dfbbdf997f5b531a2126a73a16.png) I think that there was something mistake with your nlb cluster configuration. Thanks. ### Reply 5 by gstef, 2018-03-07 thanks for replying, ``` the Wiznet module is in TCP server mode, but i cannot see in your ``` log the server connection (From 192.168.128.111 to 192.168.128.128) [![](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/1/1fb37a78dc5624bf926c6109be044b081ed8e29f.jpg) 700×66 7.6 KB](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/1/1fb37a78dc5624bf926c6109be044b081ed8e29f.jpg) ![](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/4/43cb5034a788d9ca422f3b84b96b569b59118bab.png) ![](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/b/bfde8fab40b562da87255c901cdff0fd84482681.gif) ![](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/3/3da5f28a9e3838af7e188c1f2a59fab0d1f30003.png) ![](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/1/17adbcd185931973a26842c98f8231526a35f8c8.gif) ### Reply 6 by bangbh, 2018-03-08 Hi gstef! I found out the problem! WIZ750SR can’t reply to the arp packet from the unicast nlb server when server attempts to connect to the WIZ750SR. Because of sender mac address and source mac address in the arp packet from the unicast nlb server is different. WIZ750SR response to the source mac address so unicast nlb server can’t receive the arp response from the WIZ750SR. You can see it in the following pictures. - Arp request from the unicast nlb server [![nlb%20virtual%20mac%20address%20in%20unicast%20mode](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/c/cba3732c48b118b49f5d17bfc8715a509476c43f.png) nlb%20virtual%20mac%20address%20in%20unicast%20mode769×838 22.9 KB](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/c/cba3732c48b118b49f5d17bfc8715a509476c43f.png) - Arp response from the WIZ750SR [![nlb%20wireshark%20dummy](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/0/082e2bf318fad3cdeb9dd0cc4816ced97c843b28.png) nlb%20wireshark%20dummy960×1040 27.2 KB](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/0/082e2bf318fad3cdeb9dd0cc4816ced97c843b28.png) Solution 1 If you possible, please use the multicast nlb server mode. In multicast mode, it works well. Solution 2 Open socket 0 in mac raw mode and manually respond to the arp request. Thanks. ### Reply 7 by gstef, 2018-03-08 yes, this is my problem!! ``` I'm try out some ethernet device and i found that the stak uIP ``` (or lwIP) work well. is possible to implement this stack into WiZ750SR? Thanks [![](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/1/1fb37a78dc5624bf926c6109be044b081ed8e29f.jpg) 700×66 7.6 KB](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/1/1fb37a78dc5624bf926c6109be044b081ed8e29f.jpg) ![](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/4/43cb5034a788d9ca422f3b84b96b569b59118bab.png) ![](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/b/bfde8fab40b562da87255c901cdff0fd84482681.gif) ![](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/3/3da5f28a9e3838af7e188c1f2a59fab0d1f30003.png) ![](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/1/17adbcd185931973a26842c98f8231526a35f8c8.gif) ### Reply 8 by bangbh, 2018-03-09 Our TCP/IP stack is hardware TCP/IP stack, so we can not change it easily. If you possible, please configure the NLB server to multicast mode!! I think this is the only solution for you. Sorry I can’t help you. --- Source: https://maker.wiznet.io/forum/12777