Apache HTTP Server Version 2.4

Apache > HTTP Server > Documentation > Version 2.4 > Modules

# Apache Module mod_remoteip

Description: | 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.
Status: | Base
Module Identifier: | remoteip_module
Source File: | mod_remoteip.c

### Summary

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.

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.

### Topics

- Remote IP Processing

### Directives

### Bugfix checklist

- httpd changelog
- Known issues
- Report a bug

### See also

- `mod_authz_host`
- `mod_status`
- `mod_log_config`

## 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 Directive

Description: | Declare the header field which should be parsed for useragent IP addresses
Syntax: | `RemoteIPHeader header-field`
Context: | server config, virtual host
Status: | Base
Module: | mod_remoteip

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 Directive

Description: | Declare client intranet IP addresses trusted to present the RemoteIPHeader value
Syntax: | `RemoteIPInternalProxy proxy-ip|proxy-ip/subnet|hostname ...`
Context: | server config, virtual host
Status: | Base
Module: | mod_remoteip

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 Directive

Description: | Declare client intranet IP addresses trusted to present the RemoteIPHeader value
Syntax: | `RemoteIPInternalProxyList filename`
Context: | server config, virtual host
Status: | Base
Module: | mod_remoteip

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 Directive

Description: | Declare the header field which will record all intermediate IP addresses
Syntax: | `RemoteIPProxiesHeader HeaderFieldName`
Context: | server config, virtual host
Status: | Base
Module: | mod_remoteip

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

## RemoteIPTrustedProxy Directive

Description: | Declare client intranet IP addresses trusted to present the RemoteIPHeader value
Syntax: | `RemoteIPTrustedProxy proxy-ip|proxy-ip/subnet|hostname ...`
Context: | server config, virtual host
Status: | Base
Module: | mod_remoteip

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 Directive

Description: | Declare client intranet IP addresses trusted to present the RemoteIPHeader value
Syntax: | `RemoteIPTrustedProxyList filename`
Context: | server config, virtual host
Status: | Base
Module: | mod_remoteip

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`