batman-adv

Batman advanced is a new approach to wireless networking which does no longer operate on the IP basis. Unlike the batman daemon, which exchanges information using UDP packets and sets routing tables, batman-advanced operates on ISO/OSI Layer 2 only and uses and routes (or better: bridges) Ethernet Frames. It emulates a virtual network switch of all nodes participating. Therefore all nodes appear to be link local, thus all higher operating protocols won't be affected by any changes within the network. You can run almost any protocol above batman advanced, prominent examples are: IPv4, IPv6, DHCP, IPX.

Batman advanced was implemented as a Linux kernel driver to reduce the overhead to a minimum. It does not depend on any (other) network driver, and can be used on wifi as well as ethernet lan, vpn, etc ... (anything with ethernet-style layer 2).

Configuration

Load the batman-adv module into your kernel:

$ insmod batman-adv.ko

The module is now waiting for activation. You must add some interfaces on which batman can operate. After loading the module batman advanced will scan your systems interfaces to search for compatible interfaces. Once found, it will create subfolders in the /sys directories of each supported interface, e.g.:

$ ls /sys/class/net/eth0/batman_adv/
elp_interval iface_status mesh_iface throughput_override

If an interface does not have the batman_adv subfolder, it probably is not supported. Not supported interfaces are: loopback, non-ethernet and batman's own interfaces.

Note: After the module was loaded it will continuously watch for new interfaces to verify the compatibility. There is no need to reload the module if you plug your USB wifi adapter into your machine after batman advanced was initially loaded.

The batman-adv soft-interface can be created using the iproute2 tool ip:

$ ip link add name bat0 type batadv

To activate a given interface simply attach it to the bat0 interface:

$ ip link set dev eth0 master bat0

Repeat this step for all interfaces you wish to add. Now batman starts using/broadcasting on this/these interface(s).

By reading the "iface_status" file you can check its status:

$ cat /sys/class/net/eth0/batman_adv/iface_status
active

To deactivate an interface you have to detach it from the "bat0" interface:

$ ip link set dev eth0 nomaster

All mesh wide settings can be found in batman's own interface folder:

$ ls /sys/class/net/bat0/mesh/
aggregated_ogms       fragmentation isolation_mark routing_algo
ap_isolation          gw_bandwidth  log_level      vlan0
bonding               gw_mode       multicast_mode
bridge_loop_avoidance gw_sel_class  network_coding
distributed_arp_table hop_penalty   orig_interval

There is a special folder for debugging information:

$ ls /sys/kernel/debug/batman_adv/bat0/
bla_backbone_table log         neighbors         transtable_local
bla_claim_table    mcast_flags originators
dat_cache          nc          socket
gateways           nc_nodes    transtable_global

Some of the files contain all sort of status information regarding the mesh network. For example, you can view the table of originators (mesh participants) with:

$ cat /sys/kernel/debug/batman_adv/bat0/originators

Other files allow to change batman's behaviour to better fit your requirements. For instance, you can check the current originator interval (value in milliseconds which determines how often batman sends its broadcast packets):

$ cat /sys/class/net/bat0/mesh/orig_interval
1000

and also change its value:

$ echo 3000 > /sys/class/net/bat0/mesh/orig_interval

In very mobile scenarios, you might want to adjust the originator interval to a lower value. This will make the mesh more responsive to topology changes, but will also increase the overhead.

Usage

To make use of your newly created mesh, batman advanced provides a new interface "bat0" which you should use from this point on. All interfaces added to batman advanced are not relevant any longer because batman handles them for you. Basically, one "hands over" the data by using the batman interface and batman will make sure it reaches its destination.

The "bat0" interface can be used like any other regular interface. It needs an IP address which can be either statically configured or dynamically (by using DHCP or similar services):

NodeA: ip link set up dev bat0
NodeA: ip addr add 192.168.0.1/24 dev bat0

NodeB: ip link set up dev bat0
NodeB: ip addr add 192.168.0.2/24 dev bat0
NodeB: ping 192.168.0.1

Note: In order to avoid problems remove all IP addresses previously assigned to interfaces now used by batman advanced, e.g.:

$ ip addr flush dev eth0

Logging/Debugging

All error messages, warnings and information messages are sent to the kernel log. Depending on your operating system distribution this can be read in one of a number of ways. Try using the commands: dmesg, logread, or looking in the files /var/log/kern.log or /var/log/syslog. All batman-adv messages are prefixed with "batman-adv:" So to see just these messages try:

$ dmesg | grep batman-adv

When investigating problems with your mesh network, it is sometimes necessary to see more detail debug messages. This must be enabled when compiling the batman-adv module. When building batman-adv as part of kernel, use "make menuconfig" and enable the option B.A.T.M.A.N. debugging (CONFIG_BATMAN_ADV_DEBUG=y).

Those additional debug messages can be accessed using a special file in debugfs:

$ cat /sys/kernel/debug/batman_adv/bat0/log

The additional debug output is by default disabled. It can be enabled during run time. Following log_levels are defined:

0 All debug output disabled
1 Enable messages related to routing / flooding / broadcasting
2 Enable messages related to route added / changed / deleted
4 Enable messages related to translation table operations
8 Enable messages related to bridge loop avoidance
16 Enable messages related to DAT, ARP snooping and parsing
32 Enable messages related to network coding
64 Enable messages related to multicast
128 Enable messages related to throughput meter
255 Enable all messages

The debug output can be changed at runtime using the file /sys/class/net/bat0/mesh/log_level. e.g.:

$ echo 6 > /sys/class/net/bat0/mesh/log_level

will enable debug messages for when routes change.

Counters for different types of packets entering and leaving the batman-adv module are available through ethtool:

$ ethtool --statistics bat0

batctl

As batman advanced operates on layer 2, all hosts participating in the virtual switch are completely transparent for all protocols above layer 2. Therefore the common diagnosis tools do not work as expected. To overcome these problems, batctl was created. At the moment the batctl contains ping, traceroute, tcpdump and interfaces to the kernel module settings.

For more information, please see the manpage (man batctl).

batctl is available on https://www.open-mesh.org/

Contact

Please send us comments, experiences, questions, anything :)

IRC:
#batman on irc.freenode.org
Mailing-list:
b.a.t.m.a.n@open-mesh.org (optional subscription at https://lists.open-mesh.org/mm/listinfo/b.a.t.m.a.n)

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