---
title: Simple Proxy Protocol Header
description: Format of the Simple Proxy Protocol header prepended to UDP datagrams.
image: https://developers.cloudflare.com/core-services-preview.png
---

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### Tags

[ UDP ](https://developers.cloudflare.com/search/?tags=UDP) 

# Simple Proxy Protocol Header

The client source IP and port is encoded in a fixed-length, 38-octet long header and prepended to the payload of each proxied UDP datagram in the format described below.

```

 0                   1                   2                   3

 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

|          Magic Number         |                               |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +

|                                                               |

+                                                               +

|                                                               |

+                         Client Address                        +

|                                                               |

+                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

|                               |                               |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +

|                                                               |

+                                                               +

|                                                               |

+                         Proxy Address                         +

|                                                               |

+                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

|                               |         Client Port           |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

|           Proxy Port          |          Payload...           |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


```

The contents of the header are below.

## Magic Number

16-bit fixed value set to 0x56EC for SPP. This field should be used to identify the SPP protocol and its SPP 38-byte header.

## Client Address

128-bit address of the originator of the proxied UDP datagram, that is, the client. An IPv6 address if the client used IPv6 addressing, or an IPv4-mapped IPv6 address (refer to [RFC 4291 ↗](https://tools.ietf.org/html/rfc4291)) in case of an IPv4 client.

## Proxy address

128-bit address of the recipient of the proxied UDP datagram, that is the proxy. Contents should be interpreted in the same way as the Client Address.

## Client port

16-bit source port number of the proxied UDP datagram. In other words, the UDP port number from which the client sent the datagram.

## Proxy port

16-bit destination port number of the proxied UDP datagram. In other words, the UDP port number on which the proxy received the datagram.

## Payload

Data following the header carried by the datagram. Magic number, addresses, and port numbers are encoded in network byte order.

A corresponding C structure describing the header is:

```

struct {

    uint16_t magic;

    uint8_t  client_addr[16];

    uint8_t  proxy_addr[16];

    uint16_t client_port;

    uint16_t proxy_port;

};


```

```json
{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"/directory/","name":"Directory"}},{"@type":"ListItem","position":2,"item":{"@id":"/spectrum/","name":"Spectrum"}},{"@type":"ListItem","position":3,"item":{"@id":"/spectrum/reference/","name":"Reference"}},{"@type":"ListItem","position":4,"item":{"@id":"/spectrum/reference/simple-proxy-protocol-header/","name":"Simple Proxy Protocol Header"}}]}
```