Using a GRM DNS server to locate a GRM L7 server

Using a GRM DNS server to locate the GRM L7 server

You can use one or more GRM DNS servers to direct client requests to GRM L7 servers close to the clients. (A deployment in which you are using both GRM DNS servers and GRM L7 servers is referred to as a mixed hierarchy.)

For simplicity, the following illustration shows a mixed hierarchy with only one GRM L7 server. Typically, multiple GRM DNS servers and multiple GRM L7 servers would be used.

In the previous illustration, the GRM L7 server is also configured as a GRM agent cache. The reason is that the GRM DNS agent on the GRM L7 server can report proximity measurements and health status to the GRM DNS server at the top of the hierarchy. (GRM servers cannot report this information to each other.) To determine the closest GRM L7 server to a client, the GRM DNS server uses the information reported by the agents on the GRM L7 servers to determine the distance between each GRM L7 server and the requesting client's local DNS nameserver.

The following table describes the path of the request in the previous illustration.

Stage	Description
1	The client queries its local DNS nameserver (LDNS) for the IP address of the origin server of www.netcache.com.
2	The LDNS forwards the request for resolution to the GRM DNS server that has taken over the IP address of the authoritative DNS nameserver.
3	The GRM DNS server (also acting as the authoritative DNS server responsible for the netcache.com domain) resolves the request and returns to the LDNS the IP address of the closest GRM L7 server to the client.
4	The LDNS returns the IP address of the GRM L7 server to the client in its response to the client's DNS request.
5	The client directs its request to the GRM L7 server whose IP address was returned by the LDNS.
6	The GRM L7 server applies its policies and other criteria to determine eligible caches and determines which GRM agent cache is closest to the client. The GRM L7 server then sends the rewritten request back to the client.
7	The client sends the request to the GRM agent cache to which it was redirected.
8	The GRM agent cache serves the content to the requesting client.