In this document, the migration from OpenShiftSDN to OVNKubernetes is described:
https://docs.redhat.com/en/documentation/openshift_container_platform/4.16/html/networking/ovn-kubernetes-network-plugin#initiating-limited-live-migration_migrate-from-openshift-sdn

In this documentation there is the following sentence:

"If the 100.64.0.0/16 IP address range is already in use, enter the following command to patch it to a different range. The following example uses 100.63.0.0/16."

This is not a good example. The subnet 100.63.0.0/16 falls outside the 100.64.0.0/10 network which is reserved for internal networks as described here: https://en.wikipedia.org/wiki/Reserved_IP_addresses

$ ipcalc 100.64.0.0/10
Address:   100.64.0.0           01100100.01 000000.00000000.00000000
Netmask:   255.192.0.0 = 10     11111111.11 000000.00000000.00000000
Wildcard:  0.63.255.255         00000000.00 111111.11111111.11111111
=>
Network:   100.64.0.0/10        01100100.01 000000.00000000.00000000
HostMin:   100.64.0.1           01100100.01 000000.00000000.00000001
HostMax:   100.127.255.254      01100100.01 111111.11111111.11111110
Broadcast: 100.127.255.255      01100100.01 111111.11111111.11111111
Hosts/Net: 4194302               Class A

In fact, that subnet, appears to be the property of Amazon, as shown by the following whois command:

$ whois 100.63.0.1

NetRange:       100.48.0.0 - 100.63.255.255
CIDR:           100.48.0.0/12
NetName:        AMAZO-4
NetHandle:      NET-100-48-0-0-1
Parent:         NET100 (NET-100-0-0-0-0)
NetType:        Direct Allocation
OriginAS:
Organization:   Amazon.com, Inc. (AMAZO-4)
RegDate:        2024-12-12
Updated:        2024-12-12
Ref:            https://rdap.arin.net/registry/ip/100.48.0.0

This means that if a cluster operator used 100.63.0.0/16 as a subnet for OVNKubernetes, they would risk certain Amazon networks to not be accessible / routable from within the cluster pods. Such a problem would also be fairly tricky to troubleshoot.

The following network subnets would be better examples to use:
- 100.69.0.0/16
- 100.70.0.0/16
- 100.71.0.0/16
- 100.72.0.0/16

    4.15, 4.16

    Always

    1.see docs
    2.
    3.
    

    public IP

    Private IP