Key Concepts

Understanding of the concepts listed below is required to configure a Netra Proxy Cache Array. Please refer to Figure 1-3 as you read the following definitions.

name of the Netra Proxy Cache Array

The set of hosts that form a Netra Proxy Cache Array are known to clients by a single name--the name of the DNS subdomain formed by the array--and, in fact, the array appears as a single proxy cache service to clients.

role of DNS

Each Netra Proxy Cache Array has one host that acts as the authoritative server for zone formed by the array. The remaining array hosts act as hot spares for the DNS server. Array software modifies the DNS round robin to provide load-balancing. An existing DNS server must delegate the subdomain formed by the Netra Proxy Cache Array. Chapter 2, Initial Host Configuration" provides an example of how to do this.

Netra Proxy Cache Array software

Consists of a daemon and software objects that run on each of the machines in a Netra Proxy Cache Array. The array software is what enables multiple servers to provide a single, reliable proxy cache service. On a periodic basis, the array software monitors the health (reachability, load, presence of server processes) of the hardware resources and proxy cache service on each machine. It also monitors the instance of the DNS running on one of the hosts in the array.

control network

An isolated (private) subnet over which the array software sends snapshots of the health of each machine in the array. Netra Proxy Cache Servers are equipped with a second network interface (hme1) to enable connection to a control network. This second interface is referred to as the control interface.

service address

The resource managed by the array software. This is a logical IP address that is associated with the proxy cache service on each host in the array. (There is also a service address associated with the DNS on one machine.) If a machine fails or becomes overloaded, array software can remove the availability of the service address or move the address to a different machine in the array. A critical distinction between a service address and the host IP address is that the service address can move to a different host in the array, while the host address remains fixed.

service network

The network over which server-client interactions occur. The service network is, most often, the local area network (LAN) over which clients access a variety of network services. A Netra Proxy Cache Server connects to the service network through the service interface, which is the interface (hme0) associated with the server's host name. There is no exchange of packets between the service and control networks.

Table 1-1 Interfaces and Required Addresses

Interface Name	Use	Addresses Associated with	Subnet Number
hme0	service interface, used to connect to service network	host IP address  service address for proxy cache service  service address for DNS (on one host in array)	Same subnet number used for host IP address and service address(es)
hme1	control interface, used to connect to control network	control address	Different subnet number from that used for host name and service address(es)

Figure 1-3 illustrates the concepts described above.

Figure 1-3 Example Netra Proxy Cache Array

The addresses shown in Figure 1-3 are used as examples in the configuration tables that follow. It is important to note relationship among addresses:

• The host, proxy cache service, and DNS service addresses all use the same subnet number

• The control addresses use a different subnet number from that used for the addresses mentioned in the previous bullet