It sounds to me very strange that you are able to ping HOST B from HOST A, they are not in the same subnet. It is normal that you can ping HOST C from HOST B because they are in the same subnet 10.1.0.0.
This is normal condition, instead you can see all the mac addresses from arp table because all the HOSTS are connected to the same switch.
Since you are using hosts in different network, you should need a router or static routes to reach hosts in a different subnet.
Looking at the addresses and masks: Host A is in the 10.1.1.0 subnet (range 10.1.1.0 - 10.1.1.255). Host B is in the 10.1.0.0 subnet (range 10.1.0.0 - 10.1.255.255). Host C is in the 10.1.0.0 subnet (range 10.1.0.0 - 10.1.255.255). With this configuration, all of the hosts in B and C are in the same subnet and therefore can communicate. Hosts in A are a part of the range for B and C. When a host in A is trying to communicate with a host in B or C that is in the same address range as itself, it will be successful. If the host in A trys to communicate with a host in B or C that is outside its range (10.1.1.0 - 10.1.1.255) it will look for a default gateway (router). That is why it works sometime and fails sometimes. But the answer that you need is that the addressing is screwed up. Depneding on your topology, either re-address or re-mask.
We are pleased to announce availability of Beta software for 16.6.3.
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