On the ypclient:

In /etc/default/nis set NISCLIENT=true
In /etc/yp.conf  set the yp (master and slave) server IP addresses


On the yp master+slave servers:

In /etc/yp.conf set the yp (master and slave) server IP addresses
In /etc/ypserv.securenets list all IP addresses of all yp clients so the ypserver accepts yp requests

Andreas

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