# Configure upstream HTTP/2 through Service appProtocol

Type of document: How-to guide
Product: FABRIC
> Configure NGINX Gateway Fabric to use HTTP/2 for upstream connections by setting appProtocol to kubernetes.io/h2c on a Kubernetes Service port.

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Learn how to configure NGINX Gateway Fabric to use HTTP/2 when proxying requests to upstream services using the Service port's `appProtocol` field.

## Overview

The appProtocol field on a Kubernetes Service port provides a way to specify an application protocol. Controllers such as NGINX Gateway Fabric may use this field to enable protocol-specific functionality for supported protocols. For more information, view the official [Kubernetes Service Documentation](https://kubernetes.io/docs/concepts/services-networking/service/#application-protocol).

When a Kubernetes Service port has `appProtocol` set to `kubernetes.io/h2c`, NGINX Gateway Fabric configures the corresponding NGINX location to use HTTP/2 for upstream connections by setting the [`proxy_http_version`](https://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_http_version) directive to `2` in the NGINX configuration.

## Important Notes

- `kubernetes.io/h2c` is supported on HTTPRoutes and GRPCRoutes. It isn't supported on TLSRoutes.
- When NGINX Gateway Fabric detects `kubernetes.io/h2c`, it also omits the `proxy_set_header Upgrade` and `proxy_set_header Connection` directives from the location block, because those headers are HTTP/1.1-specific and aren't used in HTTP/2 connections.

### Other supported appProtocols

In addition to the `kubernetes.io/h2c` `appProtocol`, NGINX Gateway Fabric recognizes `kubernetes.io/ws` and `kubernetes.io/wss` as described in [RFC 6455](https://www.rfc-editor.org/info/rfc6455/).

These `appProtocols` reference WebSocket over cleartext and WebSocket over TLS respectively and are supported natively by our default NGINX configuration. `kubernetes.io/ws` is only supported on HTTPRoutes and `kubernetes.io/wss` is only supported on TLSRoutes or on HTTPRoutes with an associated BackendTLSPolicy.

If an `appProtocol` on a Service port is referenced by an unsupported Route type, that backendRef will be considered invalid and status will be written to the Route.

NGINX Gateway Fabric is conformant to the information in [GEP-1911](https://gateway-api.sigs.k8s.io/geps/gep-1911/), which should be referenced for more detailed information.

## Troubleshooting

- For NGINX to set `proxy_http_version 2` for a location, all valid backend references in the routing rule must have `appProtocol: kubernetes.io/h2c` set on their Service ports. If any valid backend doesn't use `kubernetes.io/h2c`, NGINX falls back to the default HTTP/1.1.

## See also

- [Backend Protocol](https://gateway-api.sigs.k8s.io/guides/user-guides/backend-protocol/): the Gateway API guide for the `appProtocol` field.
- [GEP-1911](https://gateway-api.sigs.k8s.io/geps/gep-1911/): for more details on how NGINX Gateway Fabric interacts with `appProtocols`.
- [proxy_http_version NGINX directive](https://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_http_version).