Question: I have a simple echo server program running on CentOS 7. If I run both the client and the server in the VM, I can connect to the server.

I'm using VirtualBox with the "bridged" network configuration. Using the IP of my Linux VM (found using ifconfig), I can successfully ssh into the Linux VM from Cygwin in Windows.

However when I try to connect to the server using putty from my Windows 7 host PC the connection won't work. I don't understand why the server doesn't see a connection request from the host PC. What could be causing this? The windows Firewall is disabled.

Answer: 
I suggest you capture the packets and write them to a file with the `<file>.pcap` extension, and then open with `wireshark`.

For example, in CentOS, to capture the packets:

```
$ tcpdump -i eth0 -s 1500 -w /root/<filename.pcap>

```
as suggested by wurtel:
Use `-n` with `tcpdump` to stop it trying to resolve IP addresses to names, which can take a long time and result this issue.