en-US/system-reserved-ip-addresses.xml

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<section id="system-reserved-ip-addresses">
    <title>System Reserved IP Addresses</title>
    <para>In each zone, you need to configure a range of reserved IP addresses for the management network. This network carries communication between the &PRODUCT; Management Server and various system VMs, such as Secondary Storage VMs, Console Proxy VMs, and DHCP. </para>
    <para>The reserved IP addresses must be unique across the cloud. You cannot, for example, have a host in one zone which has the same private IP address as a host in another zone.</para>
    <para>The hosts in a pod are assigned private IP addresses.  These are typically RFC1918 addresses.  The Console Proxy and Secondary Storage system VMs are also allocated private IP addresses in the CIDR of the pod that they are created in.</para>
    <para>Make sure computing servers and Management Servers use IP addresses outside of the System Reserved IP range. For example, suppose the System Reserved IP range starts at 192.168.154.2 and ends at 192.168.154.7. &PRODUCT; can use .2 to .7 for System VMs. This leaves the rest of the pod CIDR, from .8 to .254, for the Management Server and hypervisor hosts.</para>
    <para><emphasis role="bold">In all zones:</emphasis></para>
    <para>Provide private IPs for the system in each pod and provision them in &PRODUCT;.</para>
    <para>For KVM and XenServer, the recommended number of private IPs per pod is one per host. If you expect a pod to grow, add enough private IPs now to accommodate the growth.</para>
    <para><emphasis role="bold">In a zone that uses advanced networking:</emphasis></para>
    <para>For zones with advanced networking, we recommend provisioning enough private IPs for your total number of customers, plus enough for the required &PRODUCT; System VMs. Typically, about 10 additional IPs are required for the System VMs. For more information about System VMs, see the section on working with SystemVMs in the Administrator's Guide.</para>
    <para>When advanced networking is being used, the number of private IP addresses available in each pod varies depending on which hypervisor is running on the nodes in that pod. Citrix XenServer and KVM use link-local addresses, which in theory provide more than 65,000 private IP addresses within the address block. As the pod grows over time, this should be more than enough for any reasonable number of hosts as well as IP addresses for guest virtual routers. VMWare ESXi, by contrast uses any administrator-specified subnetting scheme, and the typical administrator provides only 255 IPs per pod. Since these are shared by physical machines, the guest virtual router, and other entities, it is possible to run out of private IPs when scaling up a pod whose nodes are running ESXi.</para>
    <para>To ensure adequate headroom to scale private IP space in an ESXi pod that uses advanced networking, use one or both of the following techniques:</para>
    <itemizedlist>
        <listitem><para>Specify a larger CIDR block for the subnet. A subnet mask with a /20 suffix will provide more than 4,000 IP addresses.</para></listitem>
        <listitem><para>Create multiple pods, each with its own subnet. For example, if you create 10 pods and each pod has 255 IPs, this will provide 2,550 IP addresses.</para></listitem>
    </itemizedlist>
</section>