And thanks very much for all the comments and suggestions.

And thanks very much for all the comments and suggestions. They helped me to get on the right track. I will be posting the answer I came to.

I've worked on this for a whole day. I have 2 Manjaro/Arch computers - an older workstation and a laptop. The PC at work will be without regular network connectivity and I will regularly connect with my laptop to offload data via ethernet connection. I have connected them with a crossover cable that worked successfully at home with the same laptop and a RaspberryPi. I also cable-tested the crossover. Now at work neither computer can ping each other and the error is:

and so has the workstation except the address is 192.168.0.1. Link light is on for the network card on workstation; ethtool output shows the link is detected. Yet there is no ping/connectivity. What on earth could be wrong?

I've worked on this for a whole day. I have 2 Manjaro/Arch computers - an older workstation A and a laptop B. A work will be without regular network connectivity and I will weekly connect via crossover with my laptop to offload data. A has static IP 192.168.0.1/24 set via netctl and B has IP 192.168.0.10/24 set via a NetworkManager profile in GUI. For A the mobo ethernet port did not seem to work and I installed a PCI NIC whihc has a link light. I tried connect A and B them with a crossover cable. The cable worked successfully at home with the same laptop and a RaspberryPi. I also cable-tested the crossover it is all correct. But at work neither computer can ping each other and the error is:

and so has the workstation A except the address is 192.168.0.1; netmask is the same. Link light is on for the network card on workstation A; ethtool output on A shows the link is detected. Yet there is no ping/connectivity and on B link is not detected (message from NetworkManager, ethtool and mii-tool outputs. What on earth could be wrong?

Updates according to comments: Netmask is same on both A and B. I checked interfaces with: lshw -class network -businfo - I have configured the correct interface on A - the one which belongs to the installed Realtek PCI card. Both addresses are static with the same netmask 255.255.255.0. Cards are 10/100 standard, which is confirmed by ethtool and mii-tool.

IP route show output on B

[root@zeniba ~]# ip route show
default via 192.168.0.1 dev enp3s0 proto static metric 100 
192.168.0.0/24 dev enp3s0 proto kernel scope link src 192.168.0.10 metric 100 

and similar on A, except the address is different.

arp in non-connected state shows no hw address for the other machine, which makes sense, I guess, if at least one machine thinks there is no link.

Next update: Almost solution: I subsequently found that on computer A NetworkManager was still running, despite me having disabled it previously. I read up on this and set both NetworkManager and NetworkManager-dispatcher services to masked - which should totally prevent NM from loading. Upon next reboot everything was working absolutely fine; there was immediate connection via crossover and I could get data as expected and this survived 5 reboots. I breathed a sigh of relief and put computer A on the production-testing site. However later during the day when I tried to connect to it with laptop B I got the same problem again. On A ethernet link light is on, but B shows no link/cable disconnected message. I will try to see if in some odd way NetworkManager has come to life again, but maybe this is hardware fault? Or any other network service that is interfering with netctl?

And thanks very much for all the comments and suggestions.