Windows – What would cause alternating “Request timed out.” and “Destination host unreachable.” when using ping command

Lets first work out where the problem resides.

1. Can you access the required services on B when logged into B?
   1. You will need to restore from backup as it looks like OS has become corrupt
2. Can you acccess the required services on A when logged into A?
   1. You will need to restore from backup as it looks like OS has become corrupt
3. Can you flush and reset iptables rules on A to ensure not a corrupt firewall: iptables -X && iptables -F
4. Can you try and access services on A from B?
5. Can you use telnet on B to telnet to service port on A? eg: telnet A 80 or telnet A 25
6. Can you flush and reset iptables rules on B to ensure not a corrupt firewall: iptables -X && iptables -F
7. Can you try and access services on B from A?
8. Can you use telnet on A to telnet to service port on B? eg: telnet B 80 or telnet B 25
9. Can you restart the firewall on A and re-test from B?
10. Can you restart the firewall on B and re-test from B?

With the answers to these questions we can start deducing where the problem lies at the moment it is pure speculation where the problem lies without some real analysis and data to collaborate what the cause of the issue is.

Also worth noting:

1. Have you verified your switch is ok?
2. Have you tried other machines on this switch?
3. Have you tried other ports?
4. Have you verified the switch's configuration?

Ping works by sending a series of packets. In this case ping have sent three packets. For the first one it had a reply from the target host. For the second one, no reply at all. For the third one, no reply from the host, but a notification packet arrived from a different host saying "I can't route your packet, the destination address looks like it is on my subnet, but I can't ARP it". The host notyfying could be your own host.

So you have an unstable connection to the host. Not all packets arrive there or not all packets return, but some make it. If this host is on your LAN, this may be a switch failure, cable failure, or NIC failure.