Network Address Allocation

When you create a new cluster or data center (DC) with Instaclustr you specify a network address range that is used for internal IP address as instances are created. The network range in specified in CIDR format which is a compact representation of a range of IP addresses. The CIDR basically takes an IP address and a network prefix length, which represents a range of IP addresses (also known as CIDR block).

The network must be part of the private address space.

The specified DC network is further divided into subnetworks which are allocated for racks.

The specified network must a have network prefix between /16 to /26. This is to make sure network supports at least 3 racks having at least 10 nodes each.

Subnetting of the Data Centre Network is done in the following way

  • 2 bits reserved for specifying the rack (so 4 racks per DC)
  • remaining bits per host - 6 reserved IPs. So for example,
    • for a /26 DC Network CIDR, maximum 10 hosts per rack
    • for a /25 DC Network CIDR, maximum 26 hosts per rack
    • for a /16 DC Network CIDR, maximum 16,387 hosts per rack

These calculations are all displayed on our dashboard when you specify a network range before creating a cluster or adding a data centre.

Data centre ranges are allocated sequentially by default, or can be changed to a custom subnet when creating or adding a DC. So, if for example you specified 10.223.120.0/25 as your data centre range our system would suggest the following ranges when creating or adding data centres 10.223.120.128/25, 10.223.121.0/25, 10.223.121.128/25 ... 10.223.127.128/25, or you may choose to specify your own.

If you want to connect to your cluster via these internal addresses then you must choose the "Use private IP addresses for node discovery" option on cluster creation and then set up VPC peering to connect (in AWS. Contact support for other environments).

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