Problem when ping to w5100

Hi all,

My company used W5100 for our products. I have a problem when ping to device. I connected 5 devices + my PC to switch TP-LINK in local, then ping to all devices. It 's ok. But when i connect switch to our office network, some time, i can’t ping to one of them. Yellow red on RJ45 flash, but i receive "Destination host unreachable " messages. 70% of our products have same problem (approximately 350/500).

Any idea for my problem?


you become local connection → That is normal operate.

I think confliction to mac, ip address.

I need more detail information. How connected 5 device & switch ?

What is “Yellow red on RJ45 flash” ?

RJ-45 LED is yellow and green.

Thank you

thank you,

i sure that MAC and IP are no conflict. The Link Led flashes. i use oscilloscope to measure TX LED. When w5100 is in “destination host unreachable” state, TX LED is alway low level state

[quote=“kami90”]thank you,

i sure that MAC and IP are no conflict. The Link Led flashes. i use oscilloscope to measure TX LED. When w5100 is in “destination host unreachable” state, TX LED is alway low level state[/quote]
Hello, it is not an easy task to find out what is wrong using information you provided. In 5-device local setup when everything works properly, it is clear you do not have IP address or MAC address conflict. But when you connect switch to wider network, something wrong happens, and switch stops processing packets to specific destinations. 350/500 volume is relatively high.

If your switch is intelligent enough and is having GUI or command line go there and see what switch thinks about MAC addresses and IP addresses.
MAC address conflict may cause serious fault on the network, depending on the intelligence of the networking gateways involved. Some MAC addresses are reserved (you can not take ANY number putting it into MAC address field - do you know it?)

Thus you should check WHOLE office network, each device, one by one, seeing their hardware addresses (MACs). You will not need, most probably, check printers, notebooks or desktops, or even servers because manufacturers do not assign same MAC addresses to two cards. Most probably there’s one or more your developed devices on the office network - check such connected devices first.

I can not reproduce issue here, but the way I would go is:

  1. investigated switch state if it is intelligent and has diagnostic interface,
  2. tried “arp -a” after trying pinging the device;
  3. “nbtstat -n”
  4. meanwhile physically checking everything on the network…

I do not know what these commands display in case of network faults.

Which MAC addresses and IP addresses you use for typical 5 devices when connected to switch without office connection? Write numbers down and post here (if they are not secret).

If you need help with that, let me know (you can send emails to forum users from user’s account page).

Edit: another way to go forward. You connect only ONE your W5100 device to the switch. You ensure it works with ping for let’s say 5 minutes. Then you connect switch to office network. You reboot the device having W5100 onboard. It will then come online probably broadcasing itself on the network, making network equipment go nuts. As soon as you see this behavior (whole network stopped operating properly or device is not pingable any more) you note device’s IP and MAC addresses. If there’s MAC address conflict and device uses DHCP configuration, then DHCP server, most probably, will give the device on its boot same IP address as another conflicting device. Thus, writing down IP and MAC you will have the information about remote device. Now, after you confirmed issue, you disconnect the device from the router, and wait for some time for network to revitalize. Then you issue ping command to IP address you wrote down. Most probably you will receive response from somewhere. Now your task is find out what this device is and where this device is located.

However if your environment does not use DHCP task goes down to really checking device by device OR registry of the devices on the network (I hope your network admin has the one).