To keep track of domain names, IP has defined the concept of a name server, whose job is to hold a cache (or database) of
names appended to IP addresses. The cached information is important because the requesting DNS will not need to query for
that information again, which is why DNS works well. If a server had to query each time for the same address because it had
not saved any data, the queried servers would be flooded and would crash.
A gateway for multiple enterprise customers can be secured by mapping the remote users to a VRF domain. Mapping means obtaining
the IP address of the VRF domain for the remote users. By using VRF domain mapping, a remote user can be authenticated by
a VRF domain-specific AAA server so that the remote-access traffic can be forwarded within the VRF domain to the servers on
the corporate network.
To support traffic for multiple VRF domains, the DNS and the servers used to resolve conflicts must be VRF aware. VRF aware
means that a DNS subsystem will query the VRF name cache first, then the VRF domain, and store the returned RRs in a specific
VRF name cache. Users are able to configure separate DNS name servers per VRF.
VRF-aware DNS forwards queries to name servers using the VRF table. Because the same IP address can be associated with different
DNS servers in different VRF domains, a separate list of name caches for each VRF is maintained. The DNS looks up the specific
VRF name cache first, if a table has been specified, before sending a query to the VRF name server. All IP addresses obtained
from a VRF-specific name cache are routed using the VRF table.