Re: [B.A.T.M.A.N.] how to make IP layer handle the change of network topology

[Simon Wunderlich <sw@simonwunderlich.de>]

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



> 
> So, how should I do to make the IP layer be aware of that the gateway has
> swithed to another one?
> 
> Thanks! Best regards.
> 
> liu
---
Mit freundlichen Grüßen / kind regards
Simon Wunderlich

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