In isolated guest networks, a part of the guest IP address space can be reserved for non-CloudStack VMs or physical servers. To do so, you configure a range of Reserved IP addresses by specifying the CIDR when a guest network is in Implemented state. If your customers wish to have non-CloudStack controlled VMs or physical servers on the same network, they can share a part of the IP address space that is primarily provided to the guest network.

In an Advanced zone, an IP address range or a CIDR is assigned to a network when the network is defined. The CloudStack virtual router acts as the DHCP server and uses CIDR for assigning IP addresses to the guest VMs. If you decide to reserve CIDR for non-CloudStack purposes, you can specify a part of the IP address range or the CIDR that should only be allocated by the DHCP service of the virtual router to the guest VMs created in CloudStack. The remaining IPs in that network are called Reserved IP Range. When IP reservation is configured, the administrator can add additional VMs or physical servers that are not part of CloudStack to the same network and assign them the Reserved IP addresses. CloudStack guest VMs cannot acquire IPs from the Reserved IP Range.