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Bug 1786016

Summary:	AWS subnet prefix is created with 4 added to the CIDR of the VPC when installing a cluster on AWS using IPI.
Product:	OpenShift Container Platform	Reporter:	ryoji noma <rnoma>
Component:	Installer	Assignee:	Abhinav Dahiya <adahiya>
Installer sub component:	openshift-installer	QA Contact:	Johnny Liu <jialiu>
Status:	CLOSED NOTABUG	Docs Contact:
Severity:	medium
Priority:	unspecified	Keywords:	SupportQuestion
Version:	4.2.z
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Last Closed:	2019-12-23 13:17:13 UTC	Type:	Bug
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
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Description ryoji noma 2019-12-23 06:01:30 UTC

Description of problem:
When installing a cluster on AWS using IPI, the VPC CIDR is created with machine CIDR. And subnet prefixes are created with 4 added to the CIDR of the VPC. But there aren't document about subnet prefix. Is this behavior intended?
 
Version-Release number of selected component (if applicable):
openshift4.2
 
How reproducible:
Steps to Reproduce:
1.edit machineCIDR of install-cinfig.yaml.
ex) 10.105.0.0/20
2. ./openshift-install create cluster
3.confirm the prefix of the private and public subnet.
 
Actual results:
CIDR of private and public subnet is created as 10.105.X.0/24.
If edit machineCIDR to 10.105.0.0/16, CIDR of the private and public subnet are created as 10.105.X.0/20.
If edit machineCIDR to 10.105.0.0/19, CIDR of the private and public subnet are created as 10.105.X.0/23.
Is it the intended behavior? I couldn't find any documentation about this behavior.

Comment 1 Scott Dodson 2019-12-23 13:17:13 UTC

Yes, that's correct, each zone gets its own subnet therefore we need to subdivide the machineCIDR to allocate them.