networking: document masquerade subnet size requirement for UDN#116247
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UDNs require internalMasqueradeSubnet >= /18 (IPv4). Each UDN uses two masquerade IPs via a forward-scanning allocator capped at MaxNetworks=4096. A smaller subnet exhausts IPs after a finite number of total creates, even across delete cycles, causing CrashLoopBackOff with "out of range" errors. Add a limitation bullet to the UDN limitations module and an IMPORTANT admonition to the day-2 masquerade subnet procedure. Clusters upgraded from pre-4.17 retain the /29 default (8 IPs) and must perform the day-2 change to 169.254.0.0/17 before using UDNs. Signed-off-by: Parikshit Khedekar <pkhedeka@redhat.com>
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Summary
nw-udn-limitations.adoc:internalMasqueradeSubnetmust be/18or larger for IPv4 when UDNs are in usenw-ovn-k-day-2-masq-subnet.adocwarning UDN users about the minimum subnet size and directing pre-4.17 upgraded clusters to perform the day-2 change before creating UDNsContext
OCPBUGS-55362: clusters with small masquerade subnets hit an "out of range" crash after a finite number of UDN create/delete cycles. The OVN-Kubernetes network ID allocator uses a forward-scanning round-robin capped at MaxNetworks=4096. The masquerade IP formula (
10 + networkID×2) means the subnet must contain at least 8203 IPs — a/18minimum.Clusters installed before 4.17 retain the default
169.254.169.0/29(8 IPs), which cannot support any UDN. The existing day-2 procedure already covers how to change this; this PR adds the critical warning that UDN users must perform it on pre-4.17 upgraded clusters.Test plan
nw-udn-limitations.adoc— confirm limitation appears in UDN limitations sectionnw-ovn-k-day-2-masq-subnet.adoc— confirm IMPORTANT box appears before Prerequisites