---
title: BACKEND
summary: null
url: https://www.fastly.com/documentation/reference/vcl/types/backend
---

A compound type representing an origin server.
These can be defined via the API, CLI, web interface, or using the `backend` declaration in VCL.

```vcl
backend b1 {
  .host = "192.0.2.1";
  .port = "80";
}
```

Backends defined via the API, CLI, or web interface will generate a VCL backend definition prefixed with `F_`.  Backends defined in VCL are not prefixed.

The backend used for a request can be changed by setting the value of `req.backend`, which is typically done in `vcl_recv`.