--- 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 --- > Documentation Index > Fetch the complete documentation index at: https://developers.cloudflare.com/spectrum/llms.txt > Use this file to discover all available pages before exploring further. [Skip to content](#%5Ftop) # 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":"TechArticle","@id":"https://developers.cloudflare.com/spectrum/reference/simple-proxy-protocol-header/#page","headline":"Simple Proxy Protocol Header · Cloudflare Spectrum docs","description":"Format of the Simple Proxy Protocol header prepended to UDP datagrams.","url":"https://developers.cloudflare.com/spectrum/reference/simple-proxy-protocol-header/","inLanguage":"en","image":"https://developers.cloudflare.com/core-services-preview.png","dateModified":"2026-04-17","publisher":{"@type":"Organization","name":"Cloudflare","url":"https://www.cloudflare.com/"},"isPartOf":{"@type":"WebSite","@id":"https://developers.cloudflare.com/#website","name":"Cloudflare Docs","url":"https://developers.cloudflare.com/"},"keywords":["UDP"]} {"@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"}}]} ```