Any suggestions about configuring batman-adv gateways + modems

[Xuebing Wang <xbing6@gmail.com>]

Hi batman-adv community,

We have been building openwrt 15.05 + batman-adv mesh network for over 2 
years, they work great.

We are planning to use batman-adv gateways + 4G modems. For an example: 
our mesh network is with 20 nodes, 3 nodes have 4G modems connected.

1) My first thought is to use batman-adv gateway (with 4G modem 
connected) as dhcp server, and forward batman-adv interface to wan 
interface (modem).
1.1)  But, there is an issue with this setup. Once a modem is down, 
nodes that are connected to this batman-adv gateway (with modem) can not 
automatically "roam" to another batman-adv gateway (with good modem 
connection).
1.2)  This behavior is expected, right?

2) My second thought is to bridge batman-adv interface and wan interface 
(modem). This works great, I do not see issue (1.1) above.
-  By this setup, all batman-adv clients get ip via dhcp and via modem.
2.1)  Is this the suggested setup to use batman-adv gateways?

3) When I bridge batman-adv interface with other interface (as in step 2 
above), can I use batman-adv interface via *ipv6* to ping other 
batman-adv nodes?

Thanks.
Xuebing Wang