MULTI Network Manager (MNM) is a command line network manager for Linux, with proper support for multihoming (currently IPv4 only). It automatically detects new network interfaces, acquires an IP (using for example DHCP or read from config file) and configures the routing table(s) accordingly, using Netlink/RTNetlink-messages. MNM supports the following command line options:

• -d : Run MNM as daemon. Logs messages to the log file locatin (see below).
• -l : Log file location, defaults to /var/log/multi.log
• -u : Ensure that each interface is assigned a unique IP. Use this one with care, as DHCP has no way to gracefully reject an IP address. Instead, DHCP DECLINE is used, which causes DHCP servers to blacklist IP addresses.
• -c filename : Provide a configuration file allowing you to specify which interfaces shall be assigned a static IP (and the IP of course), as well as static metrics. An example configuration file is in the /examples-directory.

• Automatically detects new network interfaces and configures the routing subsystem accordingly.
• Proper multihoming support, the routing configuration is done so that all interfaces can be used (unlike the default Linux/ip-behavior).
• Supports specifying static IPs and metrics, using an easy configuration file format.
• Broadcasts information about network events. This enables applications to easily adapt to changes in network state. The file multi_netlinkrecv.c in /examples shows how this information can be read.

First, install the required dependencies. These are libiw, glib, libyaml and libmnl. If you are using Ubuntu or Debian, the package names are libiw-dev, libglib2.0-dev, libyaml-dev and libmnl-dev. Then, either use cmake or normal make directly to compile MNM.

Note that the library versions referenced in the CMake-file are those I have used when working on MNM lately. Please let me know if it MNM compiles and works with older versions, and I will update the CMake-file.

For MNM to work properly, other network managers (for example GNOME's) must be disabled, or interfaces have to be configured with a static IP (then MNM will configure properly). Also, make sure that no dhclient instances are running on any of the interfaces you want to configure. In order to set interfaces to automatically come up, but don't get an IP (i.e., for use with MNM), set them to manual in /etc/network/interfaces. For example:

iface eth0 inet manual
    up ifconfig $IFACE 0.0.0.0 up
    down ifconfig $IFACE down

If you are going to use MNM with PPP devices, make sure the 'nodefaultroute' option is specified. MNM will create this route automatically.

Unless a static IP is specified, MNM assumes that IPs for LAN and WLAN interfaces will be obtained using DHCP. For PPP devices, MNM assumes that an IP has been allocated by the ISP and set by the dialer.

• IPv6 support: Due to a lack of available IPv6 networks, I have not been able to add IPv6 support to MNM. This is on my schedule, but if anyone wants to contribute, that would be great.
• Improved error handling: Currently, the user is not notified when for example he or she provides an incorrect route. This is due to some tricky message handling that I have not decided on how to deal with yet. Some RTNETLINK-messages generate replies, while others don't.
• General code clean-up: The application has proven to be stable (used in a scientific test network for over a year now) and without memory leaks, but the overall structure still bears the marks of my (then) inexperience with netlink and more advanced event loop designs.

Linux supports multihoming, however, when a Linux-device is connected to multiple networks simultaneously, the kernel will often be unable to make a routing decision due to overlapping routes.

The most common technique for configuring the routing subsystem in the presence of multiple active interfaces, is to use scripts. This is a static and error prone process, that does not scale. For example, scripts and route metrics needs to be updated as new interfaces are added.

While working on my PhD, I had to make several experiments on multihomed hosts with different number of active network interfaces. After I had made one to many configuration mistakes with my setup scripts, I decided to write MNM.

If you have any questions, comments or just want to say hi, please contact me at kristian.evensen@gmail.com.