When the guest VM is resolving a domain name, it connects to a DNS Server provided by Parallels (prl_naptd). This in turn seems to ask the DNS Server that the host machine is using (typically provided by DHCP), rather than asking the host machine directly. Normally that's fine (if a little slower when it comes to cached responses), but for anyone who is currently not connected to a network (e.g. a laptop on a train), then the domain names are never be resolved. On my computer I'm running a local DNS Server, and I've created a "/etc/resolver/devcf.com", that contains the line "nameserver 127.0.0.1". This instructs the Mac to use the local DNS server to resolve any domain names for "devcf.com", and this works when I'm offline. But it does not get used by Parallels, and I'd like it to be.