Centos – Cannot ping CentOs 6 vm on ProxMox

You can't ping ports, as Ping is using ICMP which is an internet layer protocol that doesn't have ports. Ports belong to the transport layer protocols like TCP and UDP.

However, you could use nmap to see whether ports are open or not

nmap -p 80 example.com

Edit: As flokra mentioned, nmap is more than just a ping-for-ports-thingy. It's the security auditers and hackers best friend and comes with tons of cool options. Check the doc for all possible flags.

I met this problem and eventually solved it. It's the problem of the LAN we are in. For some reason my LAN doesn't allow me to manually assign IP address when there's a DHCP server out there. The Proxmox installation program use DHCP to detect the network settings and then try to assign the IP manually(by OS) without using DHCP again after reboot. The solution is to ask the system to perform DHCP again by following commands:

dhclient -r vmbr0
dhclient vmbr0

Then the problem should be solved.