Batman-adv and multiple gateways
elektra
since there have been questions off-list about operating multiple gateways with batman-adv, I have written the following brief summary.
In general, please don't hesitate to ask questions on the list, as many list members might be interested in the subject.
Since batman-adv turns the mesh into one big switch you only need to configure batman-adv gateways and clients if you want to operate more than one gateway. In this case clients will select gateways according to the metrics:
1/ Downlink/uplink speed announced by the gateway
2/ Routing metric to the gateway
3/ Gateway selection behavior of the clients can be tweaked, too. A client can choose to prefer a slower gateway with a more reliable mesh route to it, for example.
If the gateways are part of the same LAN with a single DHCP server, all you need to do is enable the feature.
If you have different uplinks behind the gateway you have to make sure that the DHCP servers don't hand out addresses that collide. Also each gateway needs a DHCP server then. Note: If clients switch the gateway in this case they have to ask for a new DHCP lease.
Batman-adv will not detect whether the announced uplink/downlink speed you set via batctl is accurate. This has to be set manually by the administrator. It is possible to change this metric on the fly. So you can use a software that measures gateway load and capacity and dynamically changes the announced link speed.
This way you can do something like gateway load balancing. However this has to be handled with caution, as such systems tend to oscillate. You are at risk to create the effect that a large number of clients quickly associate to the faster gateway. A good way to avoid it is to implement some form of hysteresis and a careful way to change this settings. Also the time it takes to get a new DHCP lease during a change has to be considered.
Some links for further information:
http://downloads.open-mesh.org/batman/manpages/batctl.8.html
http://www.open-mesh.org/wiki/batman-adv/Gateways
http://www.open-mesh.org/wiki/batman-adv/Tweaking
Cheers,
Elektra
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