Obtaining Real Client IP

Last updated: 2020-04-21 11:34:57

    Using Non-Website Traffic Forwarding Rules

    When Anti-DDoS Advanced uses non-website traffic forwarding rules, the real server needs to get the real client IP through the TOA module.
    After the business request is forwarded through layer 4 of the protective IP, the source IP address that the business server sees after receiving the packet is the egress IP address of the protective IP. In order for the server to get the real client IP, you can use the following TOA scheme. On the Linux server of the business, install the corresponding TOA kernel package and reboot the server. Then, the server can get the real client IP.

    How TOA works

    Once forwarded, the data packet will undergo SNAT and DNAT at the same time, and its source and destination addresses will be modified.
    Under the TCP protocol, in order to pass the client IP to the server, the client's IP and port are placed in the custom tcp option field during forwarding.

    #define TCPOPT_ADDR    200  
    #define TCPOLEN_ADDR 8    /* |opcode|size|ip+port| = 1 + 1 + 6 */
    
    /*
    *insert client ip in tcp option, now only support IPV4,
    *must be 4 bytes alignment.
    */
    struct ip_vs_tcpo_addr {
    __u8 opcode;
    __u8 opsize;
    __u16 port;
    __u32 addr;
    }; 

    The Linux kernel's state transits from SYN_REVC to TCP_ESTABLISHED after the listening socket receives the ACK packet of three-way handshake. At this point, the kernel will invoke the tcp_v4_syn_recv_sock function. The Hook function tcp_v4_syn_recv_sock_toa will first invoke the original tcp_v4_syn_recv_sock function, then invoke the get_toa_data function to extract the TOA OPTION from the TCP OPTION, and store it in the sk_user_data field.

    Then, inet_getname_toa hook inet_getname will be used. When the source IP address and port is obtained, the original inet_getname function will be invoked first, and then it will be checked whether sk_user_data is empty. If real IP and port can be extracted from this field, the returned values of inet_getname will be replaced with these two values.

    The client program calls getpeername in the user mode, and the client's original IP and port will be returned.

    Kernel package installation steps

    CentOS 6.x/7.x

    1. Download the installation package:
    2. Install the package file.
      rpm -hiv kernel-2.6.32-220.23.1.el6.toa.x86_64.rpm --force    
    3. Reboot the server after the installation is completed.
      reboot
    4. Run the following command to check whether the TOA module is successfully loaded.
      lsmod | grep toa
    5. If not, manually start it.
      modprobe toa
    6. Run the following command to enable automatic loading of the TOA module.
      echo "modprobe toa" >> /etc/rc.d/rc.local
      

    Ubuntu 16.04

    1. Download the installation package:
    2. Run the following command:
      dpkg -i linux-image-4.4.87.toa_1.0_amd64.deb
      The header package is optional. If needed for relevant development, install it.
    3. After the installation is completed, reboot the server, then run the lsmod | grep toa command to check whether the TOA module is loaded, and if not, start it by running the modprobe toa command.
      Run the following command to enable loading of the TOA module:
      echo "modprobe toa" >> /etc/rc.d/rc.local
      

    Debian 8

    1. Download the installation package:
    2. The installation method is the same as that for Ubuntu.
      Please download the appropriate kernel package according to the type and version of the Linux OS of your business server and follow the steps below. If there is no kernel package for your OS, please see the TOA source code installation guide below.

    TOA source code installation guide

    Source code installation

    1. Download the source code package containing the TOA patch and click the TOA patch to download the installation package.
    2. Decompress it.
    3. Edit .config by changing CONFIG_IPV6=M to CONFIG_IPV6=y.
    4. If you need to add some custom descriptions, you can edit Makefile.
    5. Run make -jn (n is the number of threads).
    6. Run make modules_install.
    7. Run make install.
    8. Modify /boot/grub/menu.lst by changing default to the newly installed kernel (the title order starts at 0).
    9. Reboot and the kernel will have TOA.
    10. Run lsmode | grep toa to check whether the TOA module is loaded, and if not, start it by running modprobe toa.

    Kernel package production

    You can make your own rpm package or use the one we provide.

    1. Install kernel-2.6.32-220.23.1.el6.src.rpm.
      rpm -hiv kernel-2.6.32-220.23.1.el6.src.rpm
    2. Generate the kernel source code directory.
      rpmbuild -bp ~/rpmbuild/SPECS/kernel.spec
    3. Copy the source code directory.
      cd ~/rpmbuild/BUILD/kernel-2.6.32-220.23.1.el6/ cp -a linux-2.6.32-220.23.1.el6.x86_64/ linux-2.6.32-220.23.1.el6.x86_64_new
    4. Apply the TOA patch to the copied source directory.
      cd ~/rpmbuild/BUILD/kernel-2.6.32-220.23.1.el6/linux-2.6.32-220.23.1.el6.x86_64_new/ 
      patch -p1 < /usr/local/src/linux-2.6.32-220.23.1.el6.x86_64.rs/toa-2.6.32-220.23.1.el6.patch
    5. Edit .config and copy it to the SOURCE directory.
      sed -i 's/CONFIG_IPV6=m/CONFIG_IPV6=y/g' .config 
      echo -e '\n# toa\nCONFIG_TOA=m' >> .config
      cp .config ~/rpmbuild/SOURCES/config-x86_64-generic
    6. Delete .config from the original source code.
      cd ~/rpmbuild/BUILD/kernel-2.6.32-220.23.1.el6/linux-2.6.32-220.23.1.el6.x86_64 
      rm -rf .config
    7. Generate the final patch.
      cd ~/rpmbuild/BUILD/kernel-2.6.32-220.23.1.el6/
      diff -uNr linux-2.6.32-220.23.1.el6.x86_64 linux-2.6.32-220.23.1.el6.x86_64_new/ >
      ~/rpmbuild/SOURCES/toa.patch
    8. Edit kernel.spec.
      vim ~/rpmbuild/SPECS/kernel.spec
      Add the following lines to ApplyOptionPath (you can also modify the names of custom kernel packages such as buildid):
      Patch999999: toa.patch
      ApplyOptionalPatch toa.patch
    9. Make an rpm package.
      rpmbuild -bb --with baseonly --without kabichk --with firmware --without debuginfo --target=x86_64 ~/rpmbuild/SPECS/kernel.spec
    10. Install the kernel rpm package.
      rpm -hiv kernel-xxxx.rpm --force
    11. Reboot to load the TOA module

    Using Website Traffic Forwarding Rules

    When Anti-DDoS Advanced uses website traffic forwarding rules, the X-Forwarded-For field in the HTTP header can be used to get the real client IP.
    X-Forwarded-For is an extended field in the HTTP header used to enable the server to identify the real IP of the clients accessing the server through proxies.
    Format:
    X-Forwarded-For: Client, proxy1, proxy2, proxy3……
    When forwarding the user access request to the real server, Anti-DDoS Advanced will record the real IP of the requesting user at the beginning of the X-Forwarded-For field. Therefore, the application on the real server only needs to get the content of the X-Forwarded-For field in the HTTP header.
    For more information, please see How to Get Real Client IP Based on Layer-7 Forwarding Rules.

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