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From: Simon Wunderlich <sw@simonwunderlich.de>
Date: Thu, 7 Aug 2014 10:32:05 +0200
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Subject: Re: [B.A.T.M.A.N.] how to make IP layer handle the change of
	network topology
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To: b.a.t.m.a.n@lists.open-mesh.org

Bah, i hit the wrong button before finishing the mail :)

> Hi liu,
> 
> > Hello, eveyone, I am learning the batman.adv recently.
> > 
> > We know that batman.adv works on layer 2. When the network topology
> > change, batman.adv can know this change and handle it. But the IP layer
> > doesn't know that. How to make IP layer handle the change of network
> > topology?
> 
> The IP layer does not need to know - to the upper layers, a batman-adv
> network appears to be a network where all nodes are just one hop away -
> although they might be more far away in practice. So if you insert an IP
> packet, it will get transported automatically to the right destination
> (provided batman-adv knows where that is), even over multiple hops.
> 
> > For example, I have 3 mesh nodes, client node A, gateway node B and
> > geteway node C. A connects  to internet via B. Then I shutdown B. I
> > guess A will switch to C as it's gateway node automatically. But it's
> > not so. A continuously send the ARP request packet to search the MAC
> > address of B. The default gateway is still B, not C.
> 
> This will only work if the gateways IP stays the same. This could work like
> that:
>  * connect B and C to the same LAN, and enable bridge loop avoidance in
> batman-adv
>  * This LAN should have only one router to the internet (e.g. your ADSL
> modem).
>  * bridge the batman-interface bat0 and you Ethernet interface eth0 using a
> linux bridge device

Please see our quick start guide for more information on the topic:

http://www.open-mesh.org/projects/batman-adv/wiki/Quick-start-guide#Mixing-
non-BATMAN-systems-with-batman-adv

> 
> > So, how should I do to make the IP layer be aware of that the gateway has
> > swithed to another one?

By using bridges, you always send to the same gateway in your LAN, which does 
not change IP or MAC addresses - so your clients don't need to be aware of the 
topology change.

Cheers,
     Simon