DNS Redirection

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Suppose you are using your Cisco router as a DNS server, and you would like to have certain domains redirected to specific servers for their lookups. This would be useful for a remote VPN site that needs to look up internal hostnames from other sites, but doesn't want to use the other site's DNS server for internet lookups. You could also use this as a centralized way of banner blocking.

This example works for any hosts in the ".local" domain (ie: myhost.local) and any PTR lookups for 192.168.x.x IPs. Note with this setup, you do not use the ip name-server x.x.x.x global command.

ip dns name-list 100 permit .*.local
ip dns name-list 100 permit .*.168.192.IN-ADDR.ARPA

ip dns view default
 domain name-server
 domain name-server

ip dns view INTERNAL
 domain name-server

ip dns view-list DNS-SERVERS
 view INTERNAL 10
  restrict name-group 100
 view default 100

When a host queries the DNS server, it checks to see if the query matches name-list 100. If it matches, it queries the INTERNAL group of servers. Otherwise, it queries the default group. Note that "default" is actually a keyword. It refers to the same set of nameservers that the router will use for lookups when executing commands (ie "ping www.google.ca").