This is a strange problem that I'm trying to sort out while working from home.
- Manufacturing plant.
- Windows 10 / Cisco environment.
Figure 1. The essentials of the layout.
- The PC on VLAN could not ping the Moxa router. I have tried rebooting the PC.
- My laptop working from home over VPN can always ping the router.
- If I reboot the Moxa router then PC on VLAN can ping the router for about two minutes - although it's sporadic.
Ping results from PC on VLAN.
c:\>ping -t 10.162.26.200
Reply from 10.162.30.133: Destination host unreachable. [Router rebooting.]
Reply from 10.162.30.133: Destination host unreachable.
Reply from 10.162.30.133: Destination host unreachable.
Reply from 10.162.26.200: bytes=32 time=1996ms TTL=64
Reply from 10.162.26.200: bytes=32 time<1ms TTL=64
Reply from 10.162.26.200: bytes=32 time<1ms TTL=64
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Reply from 10.162.26.200: bytes=32 time=5ms TTL=64
Request timed out.
Reply from 10.162.26.200: bytes=32 time=1ms TTL=64
Reply from 10.162.26.200: bytes=32 time=1ms TTL=64
Reply from 10.162.26.200: bytes=32 time=1ms TTL=64
Request timed out.
Request timed out.
Request timed out.
Reply from 10.162.26.200: bytes=32 time=1ms TTL=64
Reply from 10.162.26.200: bytes=32 time<1ms TTL=64
Reply from 10.162.26.200: bytes=32 time<1ms TTL=64
Reply from 10.162.26.200: bytes=32 time<1ms TTL=64
Reply from 10.162.26.200: bytes=32 time=1ms TTL=64
Reply from 10.162.26.200: bytes=32 time<1ms TTL=64
Request timed out.
Reply from 10.162.26.200: bytes=32 time=1ms TTL=64
Reply from 10.162.26.200: bytes=32 time=1ms TTL=64
Reply from 10.162.26.200: bytes=32 time=1ms TTL=64
...
Reply from 10.162.30.133: Destination host unreachable.
Reply from 10.162.30.133: Destination host unreachable.
Reply from 10.162.30.133: Destination host unreachable.
If I run arp -a the Moxa IP address isn't listed (but I've done very little work with arp over the years).
I have never seen a situation like this before. The router is always responding to ping requests from other devices and responds to PC on VLAN for a couple of minutes.
Can you suggests a likely cause for this and some means of testing and fixing it?
Response to comments from @user1686:
As I understand it, you're accessing the PC through a remote connection (and the home-to-PC connection never goes down)?
Correct. I'm connecting to PC on VLAN using TightVNC.
Does that go over the same VLAN as the ping requests do? Do you know the exact network layout between all 3 devices (PC, VPN, Moxa) -- i.e. how many switches are between them; whether those switches are managed (have packet counters, error counters);
Virtual LAN is dedicated to Engineering, has DHCP disabled and we assign fixed IP addresses. There is no indication that we have a duplicate IP address problem. Details on the Cisco switches, etc., are available from our IT department but their first look at the switch port for PC on VLAN didn't show up anything unusual.
... whether the problem occurs with other devices on the same VLAN (e.g. other PCs that are physically connected elsewhere)?
I don't have any convenient way of testing this but am allowed back on site tomorrow so I can check.
And does the Moxa router record any problems in its own logs?
No, I've checked the logs and can't see anything relevant.
From @harrymc:
Is the firmware of the Moxa router the latest? The latest is currently v5.4 from Dec 12, 2019.
No, it's V5.0 build 18083015. I can try an upgrade while on site tomorrow. I think it would be a bad idea to do it over VPN.
Response to comment from @redgrittybrick:
To eliminate the possibility of duplicate IP-addresses have you compared the arp cache when it works with when it doesn't? – RedGrittyBrick
C:\>arp -a 10.162.26.200 <-- Before Moxa router reboot.
No ARP Entries Found.
C:\>arp -a 10.162.26.200 <-- After reboot while ping is working.
Interface: 10.162.30.133 --- 0x2
Internet Address Physical Address Type
10.162.26.200 00-90-e8-66-1f-02 dynamic
C:\>arp -a 10.162.26.200 <-- After ping stops working again.
No ARP Entries Found.
No sign of a duplicate IP address there. (As mentioned previously, I haven't had to resort to arp much so I'm not familiar with its uses.)
