[ubuntu] Strange Network Problem

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http://ubuntuforums.org – Hello, Greetings! You may find this problem little strange. But is true. If you could guide me / help me, I would be very grateful to you! Thanks in Advance! We have two systems: A : Running windows server with IP Address B : Running Ubuntu 12.04 LTS on a virtual machine. The NAT'ed address is (internal ip address is : Till today, it was possible to send packets from B to A. Suddenly, from past 1-2 hours, we are not able to even ping from B to A. Strangely, I am able to ping from A to B (I can see this in Wireshark installed on A). And, they are on (Hardware)