Re: Gateway shut down detection takes too time from other nodes

[Simon Wunderlich <sw@simonwunderlich.de>]

On Thursday, October 23, 2025 2:28:10 PM Central European Summer Time 
mbiglari4@gmail.com wrote:
> Dear Simon,
> 
> I have a mesh network with three nodes that use 802.11s for the PHY and MAC
> layers, and BATMAN-adv on top to provide routing and mobility. Two of the
> nodes act as gateways, and the other functions as a client. The client
> selects the best gateway based on throughput.
> 
> Currently, I don’t have a DHCP server in this network — each node has a
> static IP address. The issue I’m encountering is that when the selected
> gateway node turns off, the client takes too long to switch to a new
> gateway. All nodes are using the BATMAN V routing protocol.

The setup is still not really clear to me. If you are not using DHCP but use 
static IP addresses, how do you do the selection of the best gateway? Is this 
a functionality of batman-adv, or a script?

batman-adv has the gateway feature [1] which optimizes the gateway based on 
throughput, but this is useful only with DHCP enabled - because it redirects 
your DHCP requests, nothing more, nothing less. This mechanism is rather slow, 
and changes will only happen when the IP address renewal is due.

You may also have interconnect your gateways with Ethernet, use a bridge, and 
enable BLA (bridge loop avoidance) in batman-adv. But it's not clear whether 
you do that.

Please explain your network setup in more detail, then we may be able to help.

[1] https://www.open-mesh.org/projects/batman-adv/wiki/Gateways

> 
> I believe this delay could be reduced by factoring the last connection time
> into the throughput calculation. For example, if you’re using an EWMA
> filter, you could treat a node that has been disconnected for more than 10
> seconds as having a throughput of zero. This would cause the EWMA value to
> drop quickly, allowing the client to select a new gateway sooner.

I can't really comment here unless I know which component in batman-adv would 
interact with, as explained above.

However, if you have an idea, you can also go ahead and implement those things 
yourself in batman-adv and try it out. Please note that BATMAN V is still 
considered experimental, and most networks I work with are running BATMAN IV.

Cheers,
      Simon