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Host portion

As explained in Google Anthos in Action

Host bits are the portion of an IP address that identifies individual addresses within a network prefix.

Host bits are the portion of an IP address that identifies individual addresses within a network prefix. In Anthos GKE planning, host bits determine how many node or Pod addresses a subnet can provide. section 10.2.2

Apply host-bit calculations to:

  • Size the node IP pool from the maximum nodes across clusters in a region. section 10.2.2
  • Size Pod IP space from the maximum Pods per node; when unknown, use the quota limit of 110 Pods per node. section 10.2.2
  • Combine node and Pod host-bit requirements to calculate the Pod CIDR netmask: 32 minus both values. section 10.2.2

GKE Pod CIDR sizing

For 5,000 regional nodes and 110 Pods per node, choose 13 host bits for nodes and 8 for Pods. The resulting netmask is 32 − (13 + 8) = /11. section 10.2.2

Table 10.3 Determining the required host bits

Nodes required

Host bits for nodes

1-4

3 (or /29)

5-12

4 (or /28)

13-28

5 (or /27)

29-60

6 (or /26)

61-124

7 (or /25)

125-252

8 (or /24)

253-508

9 (or /23)

509-1020

10 (or /22)

1021-2044

11 (or /21)

2045-4092

12 (or /20)

4093-8188

13 (or /19)

Use the node-capacity table to map required nodes to host bits and equivalent subnet sizes; pair it with the Pod-capacity table for per-node planning. section 10.2.2

How Google Anthos in Action covers it

How deep it goes
Calculates host bits through capacity tables and a CIDR formula, stopping short of general subnetting theory.
Examples
Uses node and Pod capacity tables plus a 5,000-node, 110-Pod-per-node calculation producing a /11 Pod CIDR.
What it assumes
Requires maximum cluster, node, and Pod counts; supplies quota-based planning when the Pod maximum is unknown.
What you can do after
Apply host-bit tables and the CIDR formula to size GKE node and Pod address ranges.
How it connects
Connects IP addresses with network prefixes, subnets, CIDR blocks, nodes, Pods, and Services.
Cover of Google Anthos in Action
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