DHCP isnt on exam blue print but is very easy to setup on a router. DNS is definitely not on ccna exam but I think there should be some general questions about both DNS and DHCP on exam because its a vital network service. DNS is very easy to setup in Linux (try BIND) or Windows (I think Windows Server 2003 Enterprise has built in DNS software).
It's a vital service, but not widely served by a router. Now it is important to understand how to pass through/route DNS.
DHCP is hardly ever routed, and hardly ever should be routed, so that's a more advanced topic.
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I wouldn't worry about it - it's not something the CCNA or even the CCNP would cover.
http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_feature_guide09186a0080087ae3.html#1022604
DHCP is hardly ever routed, and hardly ever should be routed, so that's a more advanced topic.
Because i love to experiment.... learning should be fun, especially when you have access to several routers and switches.
my favourite game is ACLs & NAT, loading IOS from rommon. (tftp and xmodem) and qemu sessions accessing routers & switches