[BUG] subnet doesn't support different routable gateway

[cybercoder]

Kube-OVN Version

v1.12.28

Kubernetes Version

not important

Operation-system/Kernel Version

not important

Description

Needs to support gateway which has not in the subnet CIDR.

Steps To Reproduce

apiVersion: kubeovn.io/v1
kind: ProviderNetwork
metadata:
  name: external
spec:
  defaultInterface: eth1
---
apiVersion: kubeovn.io/v1
kind: Vlan
metadata:
  name: vlan0
spec:
  id: 0
  provider: external
---
# create a huge fake subnet to carry the traffic.
apiVersion: kubeovn.io/v1
kind: Subnet
metadata:
  name: external
spec:
  protocol: IPv4
  cidrBlock: 192.168.128.0/17
  gateway: 192.168.128.2
  vlan: vlan0
  excludeIps:
  - 192.168.128.1..192.168.128.10

And now create the real external subnets:

apiVersion: kubeovn.io/v1
kind: Subnet
metadata:
  name: subnet-x
spec:
  protocol: IPv4
  cidrBlock: 172.18.0.0/24
  gateway: 192.168.128.2
  vlan: vlan0

Current Behavior

error syncing 'subnet-x':  gateway 192.168.128.2 is not in cidr 172.18.0/24, requeuing

Expected Behavior

need to support another gateway (which is routable).

[dosubot]

The error you're encountering is due to Kube-OVN's current validation logic, which requires the gateway IP to be within the subnet's CIDR block. This is enforced in the ValidateSubnet function, where the gateway IP is checked against the subnet's CIDR using the CIDRContainIP function ^[1].

Currently, there is no configuration option in Kube-OVN to bypass this validation or support gateways outside the subnet CIDR ^[1]. The rationale behind this enforcement is to ensure proper network configuration and avoid potential conflicts or misconfigurations ^[2].

To achieve your desired setup, you might need to modify the validation logic in the codebase or explore alternative network configurations that align with Kube-OVN's current capabilities.

To continue talking to Dosu, mention @dosu.

[oilbeater]

@cybercoder what do you mean by huge fake subnet and why you need to set another subnet subnet-x with a different cidr.

[cybercoder]

@cybercoder what do you mean by huge fake subnet and why you need to set another subnet subnet-x with a different cidr.

It allows to assign private IP addresses to the external subnet,
and use multiple subent-x, y , ... to assign public addresses with small CIDR(s) to use with EIP,FIP.

With this approach we can assign multiple Public Subnets to our environment. one /27 another /29 and so on.
There's not a huge public IPv4 address subnet IRL.