[B.A.T.M.A.N.] How to set up the communication in layer 3 in mesh node with batman.adv

[liudows]

hello, eveyone.I am a b.a.t.m.a.n. beginner.I work on openwrt with batman-adv 
2012.3.0.

There are three mesh nodes. Node A  is far from node C. A can't communicate 
with C directly, but it can commuticate with C via node B, which is  between A 
and C. The path is A <--> B <--> C.

On node A, I can run the command 'batctl ping' to node B and node C 
successfully. I can also 'ping'  the node B, but I can't 'ping' node C.
It shows that I have set up the commuication with all the nodes in layer 2, but 
I can only communicate with the neighbor in layer 3.

How can I fix this? Thanks.