Package org.apache.catalina.valves

Class RemoteIpValve

java.lang.Object
org.apache.catalina.util.LifecycleBase
org.apache.catalina.util.LifecycleMBeanBase
org.apache.catalina.valves.ValveBase
org.apache.catalina.valves.RemoteIpValve
All Implemented Interfaces:
MBeanRegistration, Contained, JmxEnabled, Lifecycle, Valve
public class RemoteIpValve extends ValveBase

Tomcat port of mod_remoteip, this valve replaces the apparent client remote IP address and hostname for the request with the IP address list presented by a proxy or a load balancer via a request headers (e.g. "X-Forwarded-For").

Another feature of this valve is to replace the apparent scheme (http/https) and server port with the scheme presented by a proxy or a load balancer via a request header (e.g. "X-Forwarded-Proto").

This valve proceeds as follows:

If the incoming request.getRemoteAddr() matches the valve's list of internal or trusted proxies:

  • Loop on the comma delimited list of IPs and hostnames passed by the preceding load balancer or proxy in the given request's Http header named $remoteIpHeader (default value x-forwarded-for). Values are processed in right-to-left order.
  • For each ip/host of the list:
    • if it matches the internal proxies list, the ip/host is swallowed
    • if it matches the trusted proxies list, the ip/host is added to the created proxies header
    • otherwise, the ip/host is declared to be the remote ip and looping is stopped.
  • If the request http header named $protocolHeader (default value X-Forwarded-Proto) consists only of forwards that match protocolHeaderHttpsValue configuration parameter (default https) then request.isSecure = true, request.scheme = https and request.serverPort = 443. Note that 443 can be overwritten with the $httpsServerPort configuration parameter.
  • Mark the request with the attribute Globals.REQUEST_FORWARDED_ATTRIBUTE and value Boolean.TRUE to indicate that this request has been forwarded by one or more proxies.
Configuration parameters
RemoteIpValve property Description Equivalent mod_remoteip directive Format Default Value
remoteIpHeader Name of the Http Header read by this valve that holds the list of traversed IP addresses starting from the requesting client RemoteIPHeader Compliant http header name x-forwarded-for
internalProxies Regular expression that matches the IP addresses of internal proxies. If they appear in the remoteIpHeader value, they will be trusted and will not appear in the proxiesHeader value RemoteIPInternalProxy Regular expression (in the syntax supported by java.util.regex) 10\.\d{1,3}\.\d{1,3}\.\d{1,3}|192\.168\.\d{1,3}\.\d{1,3}| 169\.254\.\d{1,3}\.\d{1,3}|127\.\d{1,3}\.\d{1,3}\.\d{1,3}| 100\.6[4-9]{1}\.\d{1,3}\.\d{1,3}|100\.[7-9]{1}\d{1}\.\d{1,3}\.\d{1,3}| 100\.1[0-1]{1}\d{1}\.\d{1,3}\.\d{1,3}|100\.12[0-7]{1}\.\d{1,3}\.\d{1,3}| 172\.1[6-9]{1}\.\d{1,3}\.\d{1,3}|172\.2[0-9]{1}\.\d{1,3}\.\d{1,3}| 172\.3[0-1]{1}\.\d{1,3}\.\d{1,3}| 0:0:0:0:0:0:0:1|::1
By default, 10/8, 192.168/16, 169.254/16, 127/8, 100.64/10, 172.16/12, and ::1 are allowed.
proxiesHeader Name of the http header created by this valve to hold the list of proxies that have been processed in the incoming remoteIpHeader proxiesHeader Compliant http header name x-forwarded-by
trustedProxies Regular expression that matches the IP addresses of trusted proxies. If they appear in the remoteIpHeader value, they will be trusted and will appear in the proxiesHeader value RemoteIPTrustedProxy Regular expression (in the syntax supported by java.util.regex)  
protocolHeader Name of the http header read by this valve that holds the flag that this request N/A Compliant http header name like X-Forwarded-Proto, X-Forwarded-Ssl or Front-End-Https X-Forwarded-Proto
protocolHeaderHttpsValue Value of the protocolHeader to indicate that it is an Https request N/A String like https or ON https
httpServerPort Value returned by ServletRequest.getServerPort() when the protocolHeader indicates http protocol N/A integer 80
httpsServerPort Value returned by ServletRequest.getServerPort() when the protocolHeader indicates https protocol N/A integer 443

This Valve may be attached to any Container, depending on the granularity of the filtering you wish to perform.

Regular expression vs. IP address blocks: mod_remoteip allows to use address blocks (e.g. 192.168/16) to configure RemoteIPInternalProxy and RemoteIPTrustedProxy ; as Tomcat doesn't have a library similar to apr_ipsubnet_test, RemoteIpValve uses regular expression to configure internalProxies and trustedProxies in the same fashion as RequestFilterValve does.

Sample with internal proxies

RemoteIpValve configuration:

<Valve className="org.apache.catalina.valves.RemoteIpValve" internalProxies="192\.168\.0\.10|192\.168\.0\.11" remoteIpHeader="x-forwarded-for" proxiesHeader="x-forwarded-by" protocolHeader="x-forwarded-proto" />
Request Values
property Value Before RemoteIpValve Value After RemoteIpValve
request.remoteAddr 192.168.0.10 140.211.11.130
request.header['x-forwarded-for'] 140.211.11.130, 192.168.0.10 null
request.header['x-forwarded-by'] null null
request.header['x-forwarded-proto'] https https
request.scheme http https
request.secure false true
request.serverPort 80 443

Note : x-forwarded-by header is null because only internal proxies as been traversed by the request. x-forwarded-by is null because all the proxies are trusted or internal.

Sample with trusted proxies

RemoteIpValve configuration:

<Valve className="org.apache.catalina.valves.RemoteIpValve" internalProxies="192\.168\.0\.10|192\.168\.0\.11" remoteIpHeader="x-forwarded-for" proxiesHeader="x-forwarded-by" trustedProxies="proxy1|proxy2" />
Request Values
property Value Before RemoteIpValve Value After RemoteIpValve
request.remoteAddr 192.168.0.10 140.211.11.130
request.header['x-forwarded-for'] 140.211.11.130, proxy1, proxy2 null
request.header['x-forwarded-by'] null proxy1, proxy2

Note : proxy1 and proxy2 are both trusted proxies that come in x-forwarded-for header, they both are migrated in x-forwarded-by header. x-forwarded-by is null because all the proxies are trusted or internal.

Sample with internal and trusted proxies

RemoteIpValve configuration:

<Valve className="org.apache.catalina.valves.RemoteIpValve" internalProxies="192\.168\.0\.10|192\.168\.0\.11" remoteIpHeader="x-forwarded-for" proxiesHeader="x-forwarded-by" trustedProxies="proxy1|proxy2" />
Request Values
property Value Before RemoteIpValve Value After RemoteIpValve
request.remoteAddr 192.168.0.10 140.211.11.130
request.header['x-forwarded-for'] 140.211.11.130, proxy1, proxy2, 192.168.0.10 null
request.header['x-forwarded-by'] null proxy1, proxy2

Note : proxy1 and proxy2 are both trusted proxies that come in x-forwarded-for header, they both are migrated in x-forwarded-by header. As 192.168.0.10 is an internal proxy, it does not appear in x-forwarded-by. x-forwarded-by is null because all the proxies are trusted or internal.

Sample with an untrusted proxy

RemoteIpValve configuration:

<Valve className="org.apache.catalina.valves.RemoteIpValve" internalProxies="192\.168\.0\.10|192\.168\.0\.11" remoteIpHeader="x-forwarded-for" proxiesHeader="x-forwarded-by" trustedProxies="proxy1|proxy2" />
Request Values
property Value Before RemoteIpValve Value After RemoteIpValve
request.remoteAddr 192.168.0.10 untrusted-proxy
request.header['x-forwarded-for'] 140.211.11.130, untrusted-proxy, proxy1 140.211.11.130
request.header['x-forwarded-by'] null proxy1

Note : x-forwarded-by holds the trusted proxy proxy1. x-forwarded-by holds 140.211.11.130 because untrusted-proxy is not trusted and thus, we cannot trust that untrusted-proxy is the actual remote ip. request.remoteAddr is untrusted-proxy that is an IP verified by proxy1.