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.

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
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 configvirtual 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 configvirtual 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
RemoteIPTrustedProxy 10.0.2.0/24
RemoteIPTrustedProxy gateway.localdomain RemoteIPInternalProxyList Declare client intranet IP addresses trusted to present the RemoteIPHeader value RemoteIPInternalProxyList filename server configvirtual 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
RemoteIPTrustedProxyList 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 configvirtual 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 RemoteIPTrustedProxy Declare client intranet IP addresses trusted to present the RemoteIPHeader value RemoteIPTrustedProxy proxy-ip|proxy-ip/subnet|hostname ... server configvirtual 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 configvirtual 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