IP Address Reservation in
Private IP range in Guest Networks
• 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 this CIDR for assigning IP addresses to the guest VMs.
• The CIDR for a guest network is defined say 10.1.1.0/24
(IP Range: 10.1.1.1 to 10.1.1.255)
10.1.1.1 - 10.1.1.254
The CIDR 10.1.1.0/24 is now used
by VR as DHCP range to allocate
IPs to CloudStack VMs
• Not able to use all 254 IPs for Guest VMs
• Want to plug-in physical servers or vms not managed by
CloudStack in the same network. But cannot do so !!
• Wastage of IP address space
10.1.1.1 - 10.1.1.254
The whole address space could be
allocated to Guest VMs and cannot
be used outside CloudStack
Solution: IP Reservation
Divide the large guest network into 2 address spaces
1) Guest VM CIDR: Use this only for CloudStack Guest VMs
2) Reserved Range: CloudStack will not allocate IPs to Guest
VMs from this range
Use for CloudStack
• Reserved Range will not be considered by CloudStack to
allocate IP address to the guest VMs
• Assign static IP from the Reserved Range to physical server
or non-CloudStack VMs
• Since the Reserved Range is a part of the network, it will
still be routable from the VR.
IP Reservation Considerations
• IP Reservation is supported only in Isolated Guest networks
• IP Reservation can be applied only when the network is in
• No IP Reservation is done by default.
• Guest VM CIDR specified must be a subset of the original network
• IP Reservation is applied only if no active IPs exist outside the
Guest VM CIDR in that network.
• To reset an existing IP Reservation, apply IP reservation by
specifying the value of network CIDR in the CIDR field.
How to IP Reserve
Edit the Guest Network by specifying the Guest VM CIDR in
the CIDR column
updateNetwork: Specify the guestVmCidr
listNetwork API now includes 2 new response parameters :
• networkCidr : The original Cidr of the Guest network
• reservedIpRange : Non CloudStack IPs
• The IP Reservation is not supported if active IPs are
found outside the Guest VM CIDR.
• Upgrading network offering which causes a change in
CIDR (such as upgrading an offering with no external
devices to one with external devices) IP Reservation
becomes void if any.
• Using persistent networks is a good choice as there is no
need to deploy VM to bring the network to implemented