What happened:

Provide a configuration like:

apiVersion: gateway.networking.k8s.io/v1
kind: Gateway
metadata:
  name: default
spec:
  gatewayClassName: istio
  listeners:
  - name: tcp
    port: 10001
    protocol: tcp
    allowedRoutes:
      kinds:
      - kind: TCPRoute

The result is that this resource is accepted (because "tcp" is valid protocol name), but doesn't treat it as TCP protocol (because it is not equal to TCPProtocolType constant).

What you expected to happen:

Either this resource is rejected (because the TCP protocol name is "TCP", no "tcp"), or handle it as TCP protocol.

How to reproduce it (as minimally and precisely as possible):

Anything else we need to know?:

IMHO, we can either require the ProtocolType to be treated as case-insensitive, or require all Core protocols to be uppercase.