login failed with NIS (YP)

I meet some kind of interesting problem.

When I tried to login red hat (7.2), the login fail, the user name and passwd are stored in the NIS (YP), not in this red hat machine (/etc/passwd).

I can only login as the local user of this machine, after I login, I can use "ypcat hosts", it list all machines, if I use "ypcat passwd", it lists the users and other information. It seems that the NIS is running fine.

Could you kindly tell me how to fix this problem?

Thanks,

--David