Re: [B.A.T.M.A.N.] Unterstanding gateway-mode - why do nodes have a "sticky" gateway

[Marek Lindner <lindner_marek@yahoo.de>]

On Friday, January 04, 2013 23:12:59 NicoEchániz wrote:
> > Selection class 3 and beyond do change the gateway when a better one
> > becomes available. But as you correctly pointed out these selection
> > classes don't consider the announced bandwidth for the simple reason
> > that nobody cared. In most wireless scenarios (the main playground for
> > batman-adv) the path towards the gateway turned out to be more critical
> > than the gateway's pipe to the internet.
> > 
> > Feel free to propose something if you care about having this option. The
> > necessary code shouldn't be too hard to add. Backward compatibility will
> > be more difficult to achieve.
> 
> I believe that those of us who chose to use selection class 1 would
> prefer if it were "dynamic". So if a new gateway appears, then the
> client would evaluate with the same previous criteria if it is better or
> not (considering "the gateway's advertised throughput as well as the
> link quality") and switch accordingly. I see no reason why when someone
> chooses selection class 1 she would be expecting to choose the best
> available gw once and not ever check again.
> 
> If a network is stable, when a new better gw appears in some area it
> won't be selected until nodes are restarted, and that might be a long time.

You misread my statement. Nobody needs to be convinced of the usefulness of 
such a feature (at least for what concerns myself). Somebody needs to come up 
with a solid proposal which then needs to be implemented. That is what I meant 
by saying "Feel free to propose something [..]".

Note that switching immediately as soon as a better gateway comes around isn't 
the best solution. Imagine a case in which a gateway announcing the highest 
bandwidth in your network barely is visible for your gateway client. It will 
keep switching between gateways, thereby breaking all your stateful 
connections such as: ssh, vpns, video & music streams, etc


> One other change that might be interesting would be the addition of a
> setting for how much the advertised throughput affects gw selection.
> I've seen Jan uses 96/96Mbit as advertised throughput on one router; I
> do the same on our "main gateway", but maybe it would be better if we
> could actually advertise the real throughput and have a setting to
> control how much the bandwidth difference affects the selection.

Again, feel free to propose something which can be discussed.

Cheers,
Marek