Currently the RESTAPI provides the IP addresses of guest network interfaces, but it doesn't provide the gateway and netmask. This would enable an easy way of monitoring the correct network configuration of VMs. This information will need to be collected by the guest agent, passed to VDSM, processed by the engine and displayed by the RESTAPI.
This has been initially discussed in bug 1055556.
Closing old bugs. If this issue is still relevant/important in current version, please re-open the bug.