[CentOS-virt] Network failure on KVM guest

[lhecking at users.sourceforge.net]

> There has to be some problem somewhere. Have you checked the logs? Are 
> you sure the IP config is correct? Do you have connectivity if you use 
> the NAT-ed virbr0?
 
 Yes, the setup was working fine until very recently, probably yesterday.
 All other vm have connectivity in and out.

 How do I test for "connectivity if you use the NAT-ed virbr0" ?