DNS Overview

You can configure virtual routers to act as name resolvers for Domain Name Service (DNS). DNS is a client/server mechanism that maps IP addresses to hostnames.

The name resolver is the client side of DNS and receives address-to-hostname requests from its own clients when they want to contact hosts on other networks. By polling name servers, the name resolver learns name-to-address translations for the hosts its clients want to contact.

A name server may provide the translation from its cache or may poll servers lower in the DNS hierarchy to obtain a translation. Typically, name servers at the top of the hierarchy recognize top level domain names and know which servers to contact for information about more detailed domain names. See Figure 24.

Figure 24: DNS Hierarchy Example

DNS Hierarchy Example

DNS messages from a name resolver to a name server must include the domain name for the resolver’s clients. Consequently, you must specify a default domain name for the clients. The default domain name is appended to unqualified hostnames (those without domain names).

The name resolver must be able to access at least one name server. Accordingly, you must configure a static route to a gateway that provides access to the name server and assign the name server to the name resolver. For more information, see Assigning Name Servers to the System.

Each virtual router can have its own name resolver and domain name. However, if two virtual routers use the same name servers and belong to the same local domain, you do not need to configure name resolvers on both virtual routers. For more information, see Configuring One Name Resolver for Multiple Virtual Routers.

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