ucarp - Automatic IP failover

ucarp [-i interface] [-s source address] [-v virtual id] [-p password] [-P] [-a virt addr] [-h] [-b seconds] [-k skew] [-u script] [-d script] [-r ratio] [-z shutdown] [-B daemonize] [-f facility]

ucarp allows a pair of hosts to share common IP addresses in order to provide automatic failover of an address from one machine to another. It is a portable userland implementation of the secure and patent-free Common Address Redundancy Protocol, (CARP), OpenBSD's alternative to VRRP.

ucarp supports the following command line options:

-i iface --interface=iface

The network interface to bind to.

-s srcip --srcip=srcip

The persistent source address, (real IP), associated with this interface.

-v id --vhid=vhid

The id of the virtual server [1-255].

-p pass --pass=pass

The shared password, (this gets encrypted and is not sent in the clear).

-P --preempt

Turn on preemptive failover. This causes an instance of ucarp to take over master status right away.

-a virtip --addr=virtip

The IP address of the virtual server.

-h --help

Display a brief summary of the command line options.

-b SECS --advbase=SECS

Interval in seconds that advertisements will occur, (defaults to 1 second).

-k NUM --advskew=NUM

Advertisement skew [1-255], (defaults to 0).

-u command --upscript=command

Specifies the command to run after ucarp has successfully become master, the interface name gets passed as an argument. Typically a script used to bring up the virtual address, log the result, add routes, clear arp cache entries, etc.

-d command --downscript=command

Specifies the command that is run after ucarp has transitioned to the backup state, the interface name is passed as an argument. This is typically a script used to bring down the virtual interface, log the action, remove routes, etc.

-r NUM --deadratio=NUM

Ratio used by the backup to determine how long to wait for an unresponsive master before considering it dead.

-z --shutdown

Use of this command causes the command specified by the -d argument to be invoked when ucarp shuts down.

-B --daemonize

Causes ucarp to detach from the terminal and run in the background as a daemon.

-f --facility

Set the syslog facility, defaults to daemon.

A host with a real IP of 10.1.1.10 configured to be the master in a preemptive configuration with a virtual IP of 10.1.1.252.

    ucarp -i eth0 -s 10.1.1.10 -v 10 -p secret -a 10.1.1.252 \ 
    --upscript=/etc/vip-up.sh --downscript=/etc/vip-down.sh -P 

The backup might be configured something like this.

    ucarp -i eth0 -s 10.1.1.11 -v 10 -p secret -a 10.1.1.252 \ 
    --upscript=/etc/vip-up.sh --downscript=/etc/vip-down.sh 

A machine with a real IP of 192.168.1.19 is the preferred master for a virtual IP of 10.1.12.7, broadcasts are sent every 5 seconds.

    ucarp -b 5 -s 192.168.1.19 -v 27 -p badpass -a 10.1.12.7 \ 
    -u /etc/vip-up.sh -d /etc/vip-down.sh -z 

The hot standby with an IP of 192.168.1.20 uses the following command, (note the advskew of 50 putting it at a disadvantage and making the first machine preferred).

    ucarp -b 5 -k 50 -s 192.168.1.20 -v 27 -p badpass -a 10.1.12.7 \ 
    -u /etc/vip-up.sh -d /etc/vip-down.sh -z 

ucarp was written by Frank Denis, <j@ucarp.org>.

This manual page was written by Eric Evans <eevans@sym-link.com> for the Debian system (but may be used by others). Permission is granted to copy, distribute and/or modify this document under the terms of the GNU General Public License, Version 2 any later version published by the Free Software Foundation.

On Debian systems, the complete text of the GNU General Public License can be found in /usr/share/common-licenses/GPL.