Router as primary DNS server, Server as alternate? (or vice versa)

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http://serverfault.com – We have a very small business network, with a typical cable modem hooked into a DD-WRT router. We also run a basic CentOS server that does a variety of things, including acting as the primary DNS server for the office. The reason we need an internal DNS server is because we do a lot of internal web development and use the DNS server to add/remove various local network URLs for internal website testing (like www.testsite.com.local). It's very important for us to be able to add/remove URL aliases easily to the DNS. The problem with this setup is that if we ever need to restart the CentOS serve (HowTos)