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While we saw here how to setup a Cisco Router as a Caching/Forwarding DNS Server. We can now look at how to make your Cisco Router as an Authoritative DNS server. When configured as an authoritative name server for its own local host table, the router listens on port 53 for DNS queries and then answers DNS queries using the permanent and cached entries in its own host table.

Careful consideration has to be given as this can consume considerable amount of resources like CPU cycles on the Cisco Router. If you are a small network and realise your Cisco ROuter is under utilised then there is a good business case to turn your router into a DNS server.

Enable DNS Server

From the Global configuration mode, enable the DNS server on your Cisco Router

ciscorouter# conf term

ciscorouter(config)# ip dns server

Configure as Primary DNS Server

Configures the router as the primary DNS name server for a domain (zone) and as the start of authority (SOA) record source. Unless Distributed Director is enabled, the TTL on locally defined resource records will always be ten seconds.

ciscorouter(config)# ip dns primary soa

The above command configures the Cisco Router as a Authoritative Primary DNS server for the domain "" where is the Primary DNS Server and is the email account for the postmaster (read as

Create NS Records

Create NS resource record to be returned when the DNS server is queried for the associated domain. This configuration is needed only if the zone for which the system is authoritative will also be served by other name servers

ciscorouter(config)# ip host ns

Optionally, you can also use the Caching DNS server settings along with this so the Cisc Router can act as an Authoritative DNS server for its zone and for everything else as a caching DNS server. For caching DNS Server on Cisco Router, click here

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2 Comments so far »

  1. by peterwilks, on February 26 2009 @ 5:45 am


    Can someone help me flush the DNS cache? I keep getting an error message that the command is invalid. What is the correct command? I have a Acer Aspire 3600 laptop. Thanks.

  2. by admin, on February 28 2009 @ 2:58 am


    “ipconfig /flushdns” should work. Are you trying this? If vista then you may have to run it as an administrator

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