Assumptions

I am assuming that we have two networks linked with a vpn connection (net1: 10.99.0.0/24 and net2: 10.34.132.0/24). Also I am assuming that on net1 is a functional NIS master server.

NIS MASTER: nis1.test.org 10.99.0.10
NIS SERVER: nis2.test.org 10.34.132.195

How to setup a NIS client

If you put a servername in /etc/yp.conf, make sure the server is also in /etc/hosts. Otherwise if your system boots and the network is not yet up or DNS isn't reachable, ypserv cannot resolve the servers in /etc/yp.conf and will hang!

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vim /etc/hosts

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10.99.0.10    nis1.test.org    nis1

Install the netbase, portmap and nis packages

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apt-get install nis

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Configure NIS servers

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vim /etc/yp.conf

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domain test-auth server nis1.test.org

Make domain binding persistent

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vim /etc/defaultdomain

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test-auth

Setup 'running' domain

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nisdomainname test-auth

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Update local maps search rules

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vim /etc/nsswitch.conf

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passwd:         db files compat nis
group:          db files compat nis
shadow:         db files compat nis
netgroup:       nis

Restart NIS services

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/etc/init.d/nis stop
/etc/init.d/nis start

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Make the auth process query NIS

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vim /etc/passwd

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+@gods::0:0:::
+::0:0:::/bin/false

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vim /etc/group

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+:::

Test NIS client setup

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id user
ypwhich

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Setup a NIS server slave

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vim /etc/default/nis

:%s/NISSERVER=false/NISSERVER=slave
:%s/YPPWDDIR=\/etc/YPPWDDIR=\/etc\/yp
:%s/NISMASTER=/NISMASTER=nis1.test.org
:wq

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Restart NIS server

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/etc/init.d/nis stop
/etc/init.d/nis start

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Links:
http://lyre.mit.edu/~powell/debian-howto/nis.html
http://www.server-world.info/en/note?os=Debian_6.0&p=nis
http://www.linuxhelp.in/2010/05/how-to-install-and-configure-nis-server.html