mod_remoteip
Replaces the original client IP address for the connection with the useragent IP address list presented by a proxies or a load balancer via the request headers.
Base
mod_remoteip.c
remoteip_module

This module is used to treat the useragent which initiated the request as the originating useragent as identified by httpd for the purposes of authorization and logging, even where that useragent is behind a load balancer, front end server, or proxy server.

The module overrides the client IP address for the connection with the useragent IP address reported in the request header configured with the RemoteIPHeader directive.

Additionally, this module implements the server side of HAProxy's PROXY Protocol when using the RemoteIPProxyProtocol directive.

Once replaced as instructed, this overridden useragent IP address is then used for the mod_authz_host Require ip feature, is reported by mod_status, and is recorded by mod_log_config `%a` and core `%a` format strings. The underlying client IP of the connection is available in the `%{c}a` format string.

It is critical to only enable this behavior from intermediate hosts (proxies, etc) which are trusted by this server, since it is trivial for the remote useragent to impersonate another useragent.

mod_authz_host
mod_status
mod_log_config
Proxy Protocol Spec

# Remote IP Processing

Apache by default identifies the useragent with the connection's client_ip value, and the connection remote_host and remote_logname are derived from this value. These fields play a role in authentication, authorization and logging and other purposes by other loadable modules.

mod_remoteip overrides the client IP of the connection with the advertised useragent IP as provided by a proxy or load balancer, for the duration of the request. A load balancer might establish a long lived keepalive connection with the server, and each request will have the correct useragent IP, even though the underlying client IP address of the load balancer remains unchanged.

When multiple, comma delimited useragent IP addresses are listed in the header value, they are processed in Right-to-Left order. Processing halts when a given useragent IP address is not trusted to present the preceding IP address. The header field is updated to this remaining list of unconfirmed IP addresses, or if all IP addresses were trusted, this header is removed from the request altogether.

In overriding the client IP, the module stores the list of intermediate hosts in a remoteip-proxy-ip-list note, which mod_log_config can record using the `%{remoteip-proxy-ip-list}n` format token. If the administrator needs to store this as an additional header, this same value can also be recording as a header using the directive RemoteIPProxiesHeader.

## IPv4-over-IPv6 Mapped Addresses

As with httpd in general, any IPv4-over-IPv6 mapped addresses are recorded in their IPv4 representation.

## Internal (Private) Addresses

All internal addresses 10/8, 172.16/12, 192.168/16, 169.254/16 and 127/8 blocks (and IPv6 addresses outside of the public 2000::/3 block) are only evaluated by mod_remoteip when RemoteIPInternalProxy internal (intranet) proxies are registered.

RemoteIPHeader
Declare the header field which should be parsed for useragent IP addresses
RemoteIPHeader header-field
server config
virtual host

The RemoteIPHeader directive triggers mod_remoteip to treat the value of the specified header-field header as the useragent IP address, or list of intermediate useragent IP addresses, subject to further configuration of the RemoteIPInternalProxy and RemoteIPTrustedProxy directives. Unless these other directives are used, mod_remoteip will trust all hosts presenting a RemoteIPHeader IP value.

# Internal (Load Balancer) Example

RemoteIPHeader X-Client-IP

# Proxy Example

RemoteIPHeader X-Forwarded-For
RemoteIPInternalProxy
Declare client intranet IP addresses trusted to present the RemoteIPHeader value
RemoteIPInternalProxy proxy-ip|proxy-ip/subnet|hostname ...
server config
virtual host

The RemoteIPInternalProxy directive adds one or more addresses (or address blocks) to trust as presenting a valid RemoteIPHeader value of the useragent IP. Unlike the RemoteIPTrustedProxy directive, any IP address presented in this header, including private intranet addresses, are trusted when passed from these proxies.

# Internal (Load Balancer) Example

RemoteIPHeader X-Client-IP RemoteIPInternalProxy 10.0.2.0/24 RemoteIPInternalProxy gateway.localdomain
RemoteIPInternalProxyList
Declare client intranet IP addresses trusted to present the RemoteIPHeader value
RemoteIPInternalProxyList filename
server config
virtual host

The RemoteIPInternalProxyList directive specifies a file parsed at startup, and builds a list of addresses (or address blocks) to trust as presenting a valid RemoteIPHeader value of the useragent IP.

The '`#`' hash character designates a comment line, otherwise each whitespace or newline separated entry is processed identically to the RemoteIPInternalProxy directive.

# Internal (Load Balancer) Example

RemoteIPHeader X-Client-IP RemoteIPInternalProxyList conf/trusted-proxies.lst

# conf/trusted-proxies.lst contents

    # Our internally trusted proxies;
    10.0.2.0/24         #Everyone in the testing group
    gateway.localdomain #The front end balancer

RemoteIPProxiesHeader
Declare the header field which will record all intermediate IP addresses
RemoteIPProxiesHeader HeaderFieldName
server config
virtual host

The RemoteIPProxiesHeader directive specifies a header into which mod_remoteip will collect a list of all of the intermediate client IP addresses trusted to resolve the useragent IP of the request. Note that intermediate RemoteIPTrustedProxy addresses are recorded in this header, while any intermediate RemoteIPInternalProxy addresses are discarded.

# Example

RemoteIPHeader X-Forwarded-For RemoteIPProxiesHeader X-Forwarded-By
RemoteIPProxyProtocol
Enable or disable PROXY protocol handling
RemoteIPProxyProtocol On|Off
server config
virtual host
RemoteIPProxyProtocol is only available in httpd 2.4.31 and newer

The RemoteIPProxyProtocol directive enables or disables the reading and handling of the PROXY protocol connection header. If enabled with the `On` flag, the upstream client must send the header every time it opens a connection or the connection will be aborted unless it is in the list of disabled hosts provided by the RemoteIPProxyProtocolExceptions directive.

While this directive may be specified in any virtual host, it is important to understand that because the PROXY protocol is connection based and protocol agnostic, the enabling and disabling is actually based on IP address and port. This means that if you have multiple name-based virtual hosts for the same host and port, and you enable it for any one of them, then it is enabled for all of them (with that host and port). It also means that if you attempt to enable the PROXY protocol in one and disable in the other, that won't work; in such a case, the last one wins and a notice will be logged indicating which setting was being overridden.

Listen 80 <VirtualHost *:80> ServerName www.example.com RemoteIPProxyProtocol On

#Requests to this virtual host must have a PROXY protocol # header provided. If it is missing, the connection will # be aborted </VirtualHost>

Listen 8080 <VirtualHost *:8080> ServerName www.example.com RemoteIPProxyProtocol On RemoteIPProxyProtocolExceptions 127.0.0.1 10.0.0.0/8

#Requests to this virtual host must have a PROXY protocol # header provided. If it is missing, the connection will # be aborted except when coming from localhost or the # 10.x.x.x RFC1918 range </VirtualHost>
RemoteIPProxyProtocolExceptions
Disable processing of PROXY header for certain hosts or networks
RemoteIPProxyProtocolExceptions host|range [host|range] [host|range]
server config
virtual host
RemoteIPProxyProtocolExceptions is only available in httpd 2.4.31 and newer

The RemoteIPProxyProtocol directive enables or disables the reading and handling of the PROXY protocol connection header. Sometimes it is desirable to require clients to provide the PROXY header, but permit other clients to connect without it. This directive allows a server administrator to configure a single host or CIDR range of hosts that may do so. This is generally useful for monitoring and administrative traffic to a virtual host direct to the server behind the upstream load balancer.

RemoteIPTrustedProxy
Declare client intranet IP addresses trusted to present the RemoteIPHeader value
RemoteIPTrustedProxy proxy-ip|proxy-ip/subnet|hostname ...
server config
virtual host

The RemoteIPTrustedProxy directive adds one or more addresses (or address blocks) to trust as presenting a valid RemoteIPHeader value of the useragent IP. Unlike the RemoteIPInternalProxy directive, any intranet or private IP address reported by such proxies, including the 10/8, 172.16/12, 192.168/16, 169.254/16 and 127/8 blocks (or outside of the IPv6 public 2000::/3 block) are not trusted as the useragent IP, and are left in the RemoteIPHeader header's value.

# Trusted (Load Balancer) Example

RemoteIPHeader X-Forwarded-For RemoteIPTrustedProxy 10.0.2.16/28 RemoteIPTrustedProxy proxy.example.com
RemoteIPTrustedProxyList
Declare client intranet IP addresses trusted to present the RemoteIPHeader value
RemoteIPTrustedProxyList filename
server config
virtual host

The RemoteIPTrustedProxyList directive specifies a file parsed at startup, and builds a list of addresses (or address blocks) to trust as presenting a valid RemoteIPHeader value of the useragent IP.

The '`#`' hash character designates a comment line, otherwise each whitespace or newline separated entry is processed identically to the RemoteIPTrustedProxy directive.

# Trusted (Load Balancer) Example

RemoteIPHeader X-Forwarded-For RemoteIPTrustedProxyList conf/trusted-proxies.lst

# conf/trusted-proxies.lst contents

# Identified external proxies;
192.0.2.16/28 #wap phone group of proxies
proxy.isp.example.com #some well known ISP