SYNOPSIS

fake [remove] IP_ADDRESS

DESCRIPTION

The fake utility enables the switching in of a backup server by bringing up an additional interface and using ARP spoofing to take over IP_ADDRESS.

Variants of the script have been used extensively at Zip World (http://www.zipworld.com.au/) for backing up mail, web and proxy servers. Although this system has been shown to work you are well advised to test the system thoroughly before putting it into production.

Please read the documents in /usr/share/doc/fake/ for an explanation of how fake works and for a discussion of issues surrounding its use.

OPTIONS

remove

Stop the takeover of an IP address. Without this option, fake starts the takeover of an IP address.

GLOBAL CONFIGURATION FILE

The global configuration file is in /etc/fake/.fakerc. The settings there are overridden by those in ${HOME}/.fakerc. Here is a sample configuration file.

############################################################
# Set up basic environment for fake
# Variables are set as bash variables
# i.e. <VARIABLE>=<value>
#
# Must set:
#  ARP_DELAY: Delay in seconds between gratuitous ARP
#  PID_DIR: Directory where PID files are kept
#  INSTANCE_CONFIG_DIR: Directory where specific
#   configuration files for an IP address takeover are kept
#  CLEAR_ROUTERS_FILE: New line delimited list of routers to rsh
#    to and execute "clear arp-cache"
#  FAKE_RSH: Programme to use to "rsh" to another machine
#    to obtain macaddress by running ifconfig
#
# PATH can be set here to ensure that send_arp is in the
#  path
############################################################
FAKE_HOME="/etc/fake"
#PATH=/sbin:/usr/sbin:/bin:/usr/bin
ARP_DELAY=1
CLEAR_ROUTERS_FILE="$FAKE_HOME/clear_routers"
PID_DIR="/var/run"
INSTANCE_CONFIG_DIR="$FAKE_HOME/instance_config"
#Only needed if you wish to send gratuitous ARP
#advertising the "real" mac address when turning fake off
#FAKE_RSH=ssh

INSTANCE CONFIGURATION

To configure an instance of fake, create /etc/fake/instance_config/<IP-address-to-take-over>.cfg with the following format:

SPOOF_IP=<IP-address-to-take-over>

The SPOOF_IP variable must contain the same IP address as appears in the name of the file. This is checked at run time.

IFCONFIG=TRUE|FALSE
SPOOF_NETMASK=<netmask-of-network-that-IP-address-to-take-over-is-on>
TARGET_INTERFACE=<interface-to-bring-up>

If the IFCONFIG variable is set to TRUE, the address specified by SPOOF_IP will be brought up on the interface specified by TARGET_INTERFACE; SPOOF_NETMASK and TARGET_INTERFACE must also be defined.

For obvious reasons it is very important that the TARGET_INTERFACEs of running instances of fake all be different from one another.

Optionally if you wish to rsh to the main server and advertise the "real" MAC address when turning fake off then set the following;

FOREIGN_INTERFACE=<interface-on-foreign-host-with-MAC-address-to-use>
FOREIGN_ARP=<number-of-ARPs-to-send-with-real-MAC-address>

To use this last feature in an automated fashion you will need to be able to $FAKE_RSH to $SPOOF_IP from the host that fake runs on without manual authentication. With rsh this is typically achived using .rhosts; with ssh an RSH key with an empty passphrase can be employed.

Here is an example of /etc/fake/instance_config/203.12.97.7.cfg:

SPOOF_IP=203.12.97.7
IFCONFIG=TRUE
SPOOF_NETMASK=255.255.255.0
TARGET_INTERFACE=eth0:2
FOREIGN_INTERFACE=eth0
FOREIGN_ARP=5

ACTIVATION

To activate fake, run:

fake <IP-address-to-take-over> &

Logs will be made to the local0.notice syslog facility.

On startup you should see messages in the syslog; running ifconfig should show the new interface; running route should show a route for the spoofed IP address on the new interface (which is needed so the machine that fake is running on can communicate correctly to this IP address); and running tcpdump -i <interface> arp should show the gratuitous ARP packets.

DEACTIVATION

To deactivate, run:

fake remove <IP-address-to-take-over>

As of version 1.1.2 the fake process can be sent a SIGTERM or SIGHUP to effect the removal.

On removal you should see a message in the syslog; ifconfig should show that the new interface has been removed; route should show that the new route has been removed; and tcpdump should show that the gratuitous ARP has stopped.

Note: Activating fake multiple times with the same arguments has the same effect as activating it once. Similarly, deactivating fake multiple times with the same arguments has the same effect as deactivating it once.

FILES

/etc/fake/.fakerc

/etc/fake/clear_routers

/etc/fake/instance_config/<IP-address>.cfg

/var/run/fake.<IP-address>.pid

AUTHOR

Horms <[email protected]>