Couple of things you can do
1) Check the DNS Settings on the host
2) Make sure port 80 is opened from host to vcenter
3) If vCenter is running on a Windows machine, other applications can be installed and use port 80, causing a conflict with EAM port tcp/80. So you to use different port for EAM
4) Hopefully there is no firewall between your host and vcenter.
5) Run these commands to get a better idea
Check the MTU settings esxcli network nic list
ping ++netstack=vxlan -I vmk3 1.2.3.4
6) Verify VIBS are properly installed
esxcli software vib get --vibname esx-vxlan