Re: Client (Siemens SPS) dissappears in MAC address table after a while

maas0r · ‎01-27-2021

Hi fellas,

I have a problem and I don't know how to solve this:

I have a WGB (2600)-> Switch (WS-C3560CX-8PC-S) -> Client (Siemens SPS)

After a certain time I can't ping the client from outside anymore and I can't remote connect to it. When I look at the MAC address table I can't see the client's mac address anymore (but I can still see the MAC and IP address via sh ip arp command). After I ping the client from the switch it's possible to ping the client from outside too and to connect remote.

Then it works for some hours or days and after a while the same starts over again. Can't ping, no mac address visible.

Does anyone has expierenced something similar or knows how to get rid of this failure.

Thanks in advance!

BR Lukas

HenryLeo72106 · ‎01-27-2021

In my case, it doesn't stay for longer than 2 hours. I don't know what is the actual issue. I have been trying to find the solution since three days. can anyone help?

maas0r · ‎01-27-2021

It is not happening with every SPS. But we have configured ntp servers so that the SPS sends constantly requests to the outside

patoberli · ‎01-27-2021

Could be an ARP timeout/table-removal if the SPS stops communicating after a while.

maas0r · ‎01-27-2021

Thanks for your reply.

Yeah I'm thinking about the same bc there was no entry anymore in the mac-address table. After pinging it from outside it came back online. As a workaround we used to configure NTP servers on the SPS so that it will communicate but this doesn't help in some cases. I'm not confronted often with this issue but I saw this behavior already more than a few times.

At least does anyone has an idea for a workaround? And no - we can't run a script on the SPS which is pinging 8.8.8.8 all the time

patoberli · ‎01-27-2021

You can enter fixed Mac addresses into the table on the router or increase the arp timeout. Increasing the arp timeout could have other negative effects though.

Leo Laohoo · ‎01-27-2021

@maas0r wrote:

After a certain time I can't ping the client from outside anymore and I can't remote connect to it. When I look at the MAC address table I can't see the client's mac address anymore (but I can still see the MAC and IP address via sh ip arp command). After I ping the client from the switch it's possible to ping the client from outside too and to connect remote.

Then it works for some hours or days and after a while the same starts over again. Can't ping, no mac address visible.

I see this exact behaviour all the time. This is not a network issue but a fault with the NIC drivers (bad code).
So what happens is the client "stops talking" and the switch, naturally, drops the ARP details after some time.

The next time this happens, post the complete output to the following command:

sh interface <PORT> CONTROLL