Hello Liu,
Thanks for reply. I have tried to fix this problem followed by Simon's guide. Unfortunately It stil doesn't work.I draw a pciture named 'topo.jpg' in the attachment to describe my situation.
Gateway B and C are wired to router 192.168.1.1 through their 'WAN' interface. They are in the same LAN. 'bat0' and 'eth0' are bridged by 'br-lan' interface, and are assigned a mesh subnet IP address '10.130.1.x'.
Client A connected to B and C by mesh network. 'bat0' and 'wan' is bridged by 'br-wan' in Client A. 'br-wan' is assigned a subnet IP address by DHCP server in B or C, for example '10.130.1.138'.
You are still doing routing in that scenario. Instead, you should bridge all nodes in the same network, and they should be in the same IP subnet. If you configure another WAN, you are back to routing, which will not work for that scenario.
Please configure eth0, wan and bat0 in the same bridge (e.g. br-lan) on all devices. Don't configure other bridges. Then, your devices and your client should get an IP address from the 192.168.1.x subnet, and should be able to ping 192.168.1.1, even if node A fails.
Cheers, Simon