Re: [B.A.T.M.A.N.] Enhancements for Unsolicited Neigh. Adv. / grat ARP Reply

[Simon Wunderlich <sw@simonwunderlich.de>]

Hello Linus,

thank you very much for the patch proposal.

> Hi there,
> 
> Here's a little, rough patch to illustrate the idea we discussed a little
> at the last Wireless Battle Mesh, that is forwarding the noisy IPv6
> Unsolicited Neighbor Advertisements and gratuitous ARP Replies via unicast.
> 
> Currently these ugly unsol. NAs cause about 40% of ICMPv6 multicast
> overhead in our networks here.

I think it's quite a good idea - to motivate your proposal, I'd suggest to add 
some information on how many broadcasts you think you can save in your 
networks - 40% of ICMPv6 traffic is a little vague, since we don't know how 
much of your traffic is ICMPv6 and what you have already blocked.

> 
> A little more detailed explanation with some pictures can be found here:
> 
> https://www.open-mesh.org/projects/batman-adv/wiki/Unicasting-unsolicited-n
> eighbor-advertisements

Nice page. :)

> 
> In the few, simple scenarios with bridged-in hosts in VMs, the patch
> seemed to do what it was supposed to do uppon roaming. Unsol. NAs did only
> appear on the node the host roamed away from.
> 
> If I remember correctly, there were also some worries about how this
> might work together with BLA-II. I gave it a little more thought and
> had a look at the BLA-II source code, but couldn't find any issues.

I don't see any issues either - as you've implemented, it should be similarly 
working as the DHCP requests from client.

> 
> The only BLA-II related non-ideal thing I could think of so far is
> noted in the code of this patch at the according place (but I think
> that might not matter much in practice).

You describe that this feature could be used for hot-swapping, and as far as I 
understand, turning on that feature could break IPv6 hotswapping? I don't know 
how much this is actually used and its probably not the most common thing for 
our networks (and isn't reliable anyway), but you should make you feature 
optional with a sysfs option or similar. Then users or firmware engineers can 
turn that feature on as required, just as BLA and others. 

Thanks,
     Simon