Lincoln D. Stein

NAME Load balance a host or network across two or more Internet connections.


 # get status report
 % sudo -s

 # start link monitoring and load balance across all up ISPs
 % sudo

 # load balance across "CABLE" and "DSL" only
 % sudo CABLE DSL

 # print out the routing and firewall commands that would
 # ordinarily be executed
 % -d


This script can be run on a Linux-based home router or standalone computer to load balance your network connection among two or more Internet Service Providers (ISPs). When aggregated across multiple simultaneous connections, you will achieve the sum of the bandwidth of all ISP connections. In addition, the script will continuously ping each outgoing interface and adjust routing in the event that one or more ISPs become unavailable. This provides failover.

The script can be called with no arguments, in which case it will mark all known ISPs as being up and launch the "lsm" link monitor to test each one periodically for connectivity. It can also be called with one or more symbolic names for ISP connections, as defined in load_balance.conf. These will be forced "up" and other ISP connections will be forced "down".

Other command-line options allow you to view the status of your ISP connections, kill a running lsm, and more.

Generally this script must be run as root, since it alters the routing table and firewall rules.

For full installation and configuration instructions, please see


Each command-line option can be abbreviated or used in long-form.

 --debug, -d     Turn on debugging. In this mode, no firewall or
                 routing commands will be executed, but instead
                 will be printed to standard output for inspection.

 --verbose, -v   Verbose output. Echo all route and iptables commands
                 to STDERR before executing them.

 --Version, -V   Print version of Net::ISP::Balance.

 --status,-s     Print current status of each monitored ISP interface
                 to STDOUT.

 --kill,-k       Kill any running lsm process.

 --flush,-f      Flush all firewall chains and rules. If not given, then
                 the default is to try to keep custom iptables rules 
                 introduced by firewall utilities such as fail2ban and

 --help,-h       Print this message.


This section describes common usage patterns. Note that must always be run as root.

 % sudo
 % sudo CABLE
Bring up the listed ISP service, leaving the other(s) in their current state. This is usually done behind the scenes by lsm.
 % sudo up CABLE
Bring down the listed ISP service, leaving the other(s) in the current state. This is usually done behind the scenes by lsm:
 % sudo down CABLE
 % sudo -s
 % sudo -k
 % sudo -d


This section gives locations of important files.

Debian/Ubuntu/Mint systems

 /etc/network/balance.conf        # Main configuration file
 /etc/network/balance/firewall/   # Additional firewall rules
 /etc/network/balance/routes/     # Additional routing rules

RedHat/CentOS systems

 /etc/sysconfig/network-scripts/balance.conf        # Main configuration file
 /etc/sysconfig/network-scripts/balance/firewall/   # Additional firewall rules
 /etc/sysconfig/network-scripts/balance/routes/     # Additional routing rules

Format of the balance.conf:

balance.conf is the main configuration file. It defines the interfaces connected to the ISPs and to the LAN (if running on a router). Here is a typical example:

 #service    device   role     ping-ip         weight  gateway
 CABLE       eth0     isp     1     default
 DSL         eth1     isp     1     default
 LAN         eth2     lan      

 # name=value pairs define lsm configuration variables

There are two parts of the configuration file. The first part, which is required, is a four-column table that defines interfaces to be monitored.

The first column is a service name that is used to bring up or down the needed routes and firewall rules.

The second column is the name of the network interface device that connects to that service.

The third column is either "isp" or "lan". There may be any number of these. The script will load balance traffic across all ISPs, and will act as a firewall between the LAN (if any) and the Internet. You do not need to have a "lan" entry if this is a standalone host.

The fourth column (optional) is the IP address of a host that can be periodically pinged to test the integrity of each ISP connection. If too many pings failed, the service will be brought down and all traffic routed through the remaining ISP(s). The service will continue to be monitored and will be brought up when it is once again working. Choose a host that is not likely to go offline for reasons unrelated to your network connectivity, such as, or the ISP's web site. If this column is absent or marked "default", then the host will default to

The fifth column (optional) is a weight to assign to the service, and is only valid for ISP rows. If weights are equal, traffic will be apportioned evenly between the two routes. Increase a weight to favor one ISP over the others. For example, if "CABLE" has a weight of 2 and "DSL" has a weight of 1, then twice as much traffic will flow through the CABLE service. If this column is omitted or marked "default", then equal weights are assumed.

The sixth column (optional) is the IP address for the gateway host for this service. If absent or named "default", the system will attempt to guess the proper gateway automatically. Note the guessing algorithm relies on the fact that the gateway is almost always the first address in the IP range for the subnetwork. If this is not the case, then routing through the interface won't work properly. Add the correct gateway IP address manually to correct this.

The second (optional) part of the configuration file is a series of name=value pairs that allow you to customize the behavior of lsm, such as where to send email messages when a link's status changes. Please see for the comprehensive list.




Lincoln Stein,

Copyright (c) 2014-2017 Lincoln D. Stein

This package and its accompanying libraries is free software; you can redistribute it and/or modify it under the terms of the GPL (either version 1, or at your option, any later version) or the Artistic License 2.0.