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

[Simon Wunderlich <sw@simonwunderlich.de>]

On Wednesday, April 15, 2026 5:10:23 PM Central European Summer Time Simon 
Wunderlich wrote:
> Hi Martin,
> 
> On Tuesday, April 7, 2026 3:46:59 PM Central European Summer Time
> 
> martinvdberg@gmail.com wrote:
> > I think I have a similar use-case as the original poster and ran into the
> > same problem.
> > 
> > Let me try to explain:
> > 
> > - Given a mesh network where each node is assigned a *static IP*.
> > - In the mesh network there are some nodes acting as a Gateway.
> > - The other nodes in the mesh are clients.
> > - Using BATMAN-V
> > 
> > Each client node has a script running, when it detects "batctl gwl" to
> > elect another gateway, the script will set the gateway's IP-address as
> > default route: "ip route replace default via $gateway_ip dev bat0".
> > 
> > Now whenever a mesh-gateway is turned off, it will take 200 seconds before
> > it is removed from the originators and only then "batctl gwl" will elect
> > another gateway. This results in some client nodes have no internet for
> > 200
> > seconds.
> > 
> > So far, I haven't been able to get batman-adv (using batctl) to switch to
> > another gateway sooner, e.g. after 10 or 20 seconds.
> > 
> > 
> > Using DHCP is not an option in my use-case.
> > 
> > Is there somehow a way to reduce the 200 seconds? Possibly by switching to
> > BATMAN-IV?
> > 
> > Regards, Martin
> 
> that's an interesting use case, although I would like to make clear that the
> gateway feature was designed for DHCP in mind, yet you use it with static
> IPs. The main purpose was to re-route DHCP packets to the selected gateway.
> Nethertheless, you could still use this mechanism for "signaling".
> 
> The gateway selection can be based on TQ or on bandwidth parameters, but
> there is no option to speed up the "dead marking" from the 200s of the
> originator timeout. you can decrease that number in the source code, but I
> would actually advise to use a completely different method independent of
> batman-adv - for example by using a layer 3 routing daemon, or another
> application which regularly signals their availability as a gateway. For
> DHCP (which it was originally designed for), lease times are typically 5
> minutes minmum, so the 200s timeout are not really a problem there ... but
> I acknowledge that it's not really useful for "fast" switching.

Perhaps one more practical idea: You could parse the gateway list and the 
originator list yourself (batctl has json output options). Then, you could get 
the "last seen" value from the originator list, and combine it with your 
gatewaylist. In that way, you could easily filter the "best gateway which was 
last seen <20 s" in a script. This doesn't help with batmans internal DHCP 
forwarding, but since you use static IPs anyway and probably already use a 
script to get the current gateway to look up the IP, this may be an easy fix 
...

Cheers,
       Simon