[B.A.T.M.A.N.] Using batman L2 on multiple wireless cards

Simon Wunderlich simon.wunderlich at s2003.tu-chemnitz.de
Sat Feb 14 10:17:12 UTC 2009

Hello Gargi,

the design of the main interface in BATMAN has the effect that only
OGM packets from the main interface are distritibuted over the whole
network. OGM packets from secondary interfaces are only sent with TTL=1,
that means the next neighbor will drop them. 

The reason for this system is that the secondary interfaces need an unique 
ID/MAC (not the same address as the main interface), because physically this
address must be used to send the frames. The "secondary neighbor" will want 
to send only to the main interface, because this address is known 
in the whole mesh. The "secondary neighbor" therefore needs to address
the "secondary interface" correctly, so he (and he alone) receives the 
secondary OGMs. This allows the neighbor to build a route to the main 
Flooding the secondary OGMs throughout the mesh would have been another
possible alternative, but thats redundandant, and we don't want to flood
too much.

Hope that makes it somewhat clear. ;)

The consequence is that by design you won't see the secondary interfaces
of the nodes if you're not physically connected (and in range) with

> I am wondering why
> Node A: Cannot reach mac 23
> Node B: Cannot reach mac 23
> Node C: Cannot reach 20, 22

So i guess for your scenario 22 is As secondary interface, 20 is Bs
secondary interface, and 23 is Cs secondary interface.

You can verify that with your local setups: The first interface added is
the main interface, the following ones are the secondary interfaces.

best regards,

On Fri, Feb 13, 2009 at 02:58:03PM -0600, Gargi Purohit wrote:
> > Yes, batman has the concept of "main interface" (the first given interface) to
> > reduce overhead but on the node that has 2 interfaces you should see both
> > interfaces in the originator table (on a more distant host this might be
> > different).
> > Could you post the important lines from originators and explain the
> > corresponding setup ?
> Ok...now I get that...However I think not always I am able to
> reproduce this scenario.  I have node A, node B, node C - each with 2
> radios
> --ch60---| A |---ch56---------ch56---| B |---ch40-------ch40---| C |---ch48
>       (1C)..........(22)...............(20)............(21).................(1D).........(23)...
> The terminating mac addresses for the radios are shown in ( )
> My originator tables for node a, b, c are as follows:
> For Node A
> =======
> root at OpenWrt:/# cat /proc/net/batman-adv/originators
>   Originator     (#/255)           Nexthop [outgoingIF]:   Potential nexthops .
> 00:02:6f:52:80:20  (255) 00:02:6f:52:80:20 [      ath1]: 00:02:6f:52:80:20 (255)
> 00:02:6f:52:80:1d  (177) 00:02:6f:52:80:20 [      ath1]: 00:02:6f:52:80:20 (177)
> 00:02:6f:52:80:21  (255) 00:02:6f:52:80:20 [      ath1]: 00:02:6f:52:80:20 (255)
> For Node B
> =======
> root at OpenWrt:/# cat /proc/net/batman-adv/originators
>   Originator     (#/255)           Nexthop [outgoingIF]:   Potential nexthops .
> 00:02:6f:52:80:22  (255) 00:02:6f:52:80:22 [      ath1]: 00:02:6f:52:80:22 (255)
> 00:02:6f:52:80:1d  (250) 00:02:6f:52:80:1d [      ath0]: 00:02:6f:52:80:1d (250)
> 00:02:6f:52:80:1c  (255) 00:02:6f:52:80:22 [      ath1]: 00:02:6f:52:80:22 (255)
> For Node C
> =======
> root at OpenWrt:/# cat /proc/net/batman-adv/originators
>   Originator     (#/255)           Nexthop [outgoingIF]:   Potential nexthops .
> 00:02:6f:52:80:1c  (241) 00:02:6f:52:80:21 [      ath0]: 00:02:6f:52:80:21 (241)
> 00:02:6f:52:80:21  (255) 00:02:6f:52:80:21 [      ath0]: 00:02:6f:52:80:21 (255)
> I am wondering why
> Node A: Cannot reach mac 23
> Node B: Cannot reach mac 23
> Node C: Cannot reach 20, 22
> Should they be able to reach out "each of the radios" on "a node" or
> "just one of the radios" on "the node". Sometimes they can and some
> times they dont seem to..
> For instance...
> I am not sure if it is more of a radio issue than software problem...
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