Network Address Allocation

When you create a new cluster with Instaclustr you specify a network address range that is used for internal IP address as instances are created. If you want to connect to your cluster via this 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).

This article explains how we divide up the specified network range to determine the IPs allocated to each node as they are created (which might be important for your network planning).

The network range in specified in CIDR format  (https://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing, http://www.ipaddressguide.com/cidr) 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 private address space (https://en.wikipedia.org/wiki/Private_network#Private_IPv4_address_spaces) . The specified cluster network is divided into subnetworks for use by DC and each DC network is further divided into subnetworks which are allocated for racks. Following rules are enforced on network settings to facilitate further expansions and maintenance.

  • Cluster Network must have network prefix in the range /12 to /22 .
  • Data Centre Network, which must be a subnet of cluster network, can have network prefix up to /26. This is to make sure network supports 16 DCs with each DC supporting at least 3 racks having at least 10 nodes each.

Subnetting of the Cluster Network is done in the following way

  • 4 bits reserved for specifying the data center network (so allows 16 DCs per cluster)
  • 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, 10 hosts per rack
    • for a /25 DC Network CIDR, 26 hosts per rack
    • for a /16 Cluster CIDR CIDR, 1018 hosts per rack, per DC (if default suggested DC Network is used)

 

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

Within the cluster range, data center ranges are allocated sequentially by default and can be changed to different subnet when creating or adding a DC . So, if for example you specified 10.223.120.0/21 as your cluster range our system would suggest the following ranges when creating or adding data centres 10.223.120.0/25, 10.223.120.128/25, 10.223.121.0/25, 10.223.121.128/25 ... 10.223.127.128/25.

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