[CentOS] SSH problems (from the beginning)

I have 2 machines, one with CentOs4.3 (A) the other with WhiteBox 4(B). The machine A have a new installtion, the machine B has an already exists installation. The machine A has the installytion as is (except tah i choose an IP adress for eth0) 200.118.115.241 from the graphical interface on Hosts Label The machine B has eth0 and eth1, it works as proxy i can connect by ssh from A to B i can ping B from A i can not connect by ssh from B to A i can`t ping A from B if i do NSLOOKUP in A the reponse is Server inexistent

What im doing bad?

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