The working mechanism behind the Proxy Protocol

This section describes how AxoSyslog supports the Proxy Protocol.

The working mechanism behind the Proxy Protocol

When using the Proxy Protocol during load balancing, AxoSyslog detects the information behind connections connected to the load balancer, then parses the injected information into the following macros:

Data	Macro in version 4.9 and earlier	Version 4.10 and later
Source IP of the proxy	`PROXIED_SRCIP`	`SOURCEIP`
Source port of the proxy	`PROXIED_SRCPORT`	`SOURCEPORT`
Destination IP of the proxy	`PROXIED_DSTIP`	`DESTIP`
Destination port of the proxy	`PROXIED_DSTPORT`	`DESTPORT`
IP version of the connection	`PROXIED_IP_VERSION`	`IP_PROTO`

Note

Consider the following about macros and headers:

When the proxy protocol header is PROXY UNKNOWN, no additional macros are added.

When AxoSyslog cannot parse a proxy protocol header, the connection is closed:

[2020-11-20T17:33:22.189458] PROXY protocol header received; line='PROXYdsfj'
[2020-11-20T17:33:22.189475] Error parsing PROXY protocol header;
[2020-11-20T17:33:22.189517] Syslog connection closed; fd='13', client='AF_INET(127.0.0.1:51665)', local='AF_INET(0.0.0.0:6666)'
[2020-11-20T17:33:22.189546] Freeing PROXY protocol source driver; driver='0x7fffcba5bcf0'
[2020-11-20T17:33:22.189600] Closing log transport fd; fd='13'

Note Originally, the driver supported version 1 of the PROXY protocol (TCP4, TCP6, and TLS connections). PROXY protocol v2 support is available in AxoSyslog version 4.1 and later. UDP transport support for PROXY protocol v2 (proxied-udp) is available in version 4.25 and later.

Last modified September 30, 2026: Fix proxy-protocol related typos (40a5e3e4)