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OCPBUGS-87249: on AWS, select associated IPv6 CIDR block for egress IP subnet #228

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OCPBUGS-87249: on AWS, select associated IPv6 CIDR block for egress IP subnet #228

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27 changes: 18 additions & 9 deletions pkg/cloudprovider/aws.go
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Original file line number Diff line number Diff line change
Expand Up @@ -276,23 +276,32 @@ func (a *AWS) getSubnet(networkInterface *ec2.InstanceNetworkInterface) (*net.IP
var v4Subnet, v6Subnet *net.IPNet
subnet := describeOutput.Subnets[0]
if subnet.CidrBlock != nil && *subnet.CidrBlock != "" {
_, subnet, err := net.ParseCIDR(*subnet.CidrBlock)
_, v4Net, err := net.ParseCIDR(*subnet.CidrBlock)

@arghosh93 arghosh93 Jul 14, 2026

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Why do you have to change the variable name here?

@jechen0648 jechen0648 Jul 14, 2026

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this subnet variable is used for v4 and v6 below, it's like one variable used for two different ipstack types, it is easy to get confused , that is why I changed the variable name. But I can revert if you prefer minimal change

if err != nil {
return nil, nil, fmt.Errorf("error: unable to parse IPv4 subnet, err: %v", err)
}
v4Subnet = subnet
v4Subnet = v4Net
}

// I don't know what it means to have several IPv6 CIDR blocks defined for
// one subnet, specially given that you can only have one IPv4 CIDR block
// defined...¯\_(ツ)_/¯
// Let's just pick the first.
if len(subnet.Ipv6CidrBlockAssociationSet) > 0 && subnet.Ipv6CidrBlockAssociationSet[0].Ipv6CidrBlock != nil && *subnet.Ipv6CidrBlockAssociationSet[0].Ipv6CidrBlock != "" {
_, subnet, err := net.ParseCIDR(*subnet.Ipv6CidrBlockAssociationSet[0].Ipv6CidrBlock)
// A subnet can have multiple IPv6 CIDR block associations (e.g., a previous
// "disassociated" one and a current "associated" one). On dualstack AWS clusters
// after subnet CIDR changes, picking the wrong (stale) CIDR causes egress IP
// assignment to fail because OVN-Kubernetes selects IPs from the wrong range.
// Always select the first association in "associated" state.
for _, assoc := range subnet.Ipv6CidrBlockAssociationSet {
if assoc.Ipv6CidrBlock == nil || *assoc.Ipv6CidrBlock == "" {
continue
}
if assoc.Ipv6CidrBlockState == nil || assoc.Ipv6CidrBlockState.State == nil ||
*assoc.Ipv6CidrBlockState.State != ec2.SubnetCidrBlockStateCodeAssociated {
continue
}
_, v6Net, err := net.ParseCIDR(*assoc.Ipv6CidrBlock)
if err != nil {
return nil, nil, fmt.Errorf("error: unable to parse IPv6 subnet, err: %v", err)
}
v6Subnet = subnet
v6Subnet = v6Net
break
}

return v4Subnet, v6Subnet, nil
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