I have multiple servers deployed behind a single switch. All the servers have their own public IP addresses. Suddenly one of them (say A) cannot be accessed from the outside by any means, e.g. HTTP, SSH, etc. However, I can ssh into some other server (say B) behind the same switch, and then can successfully access HTTP and SSH services on machine A. By ssh into A on B, I can also access services provided by B on A, but from A I cannot access anything outside the switch.
I tried to restart machine A as well as the switch, but nothing good happens. At the same time, there are very very short slots of times that I CAN access A outside the switch, but then CANNOT access again all of a sudden. To me it doesn't make sense at all.
The OS on machine A is Ubuntu 12.04 and connected to the switch via normal Ethernet. I can ping to all the machines behind the switch, but cannot ping anything else (doesn't fail, but hangs). All the processes running on A are as normal as before.
btw, the network monitoring administrators told me that some machine behind the switch has been sending out packages frequently during the last week without receiving that much. That may be related to this failure.