Specifications

Chapter 9: Administering Geographic Clusters

150 Equalizer Installation and Administration Guide

It does this by sending a geographic query protocol probe (GQP) to each site; the probe is

received by a special Envoy agent running at each site in the cluster (the agent for a site is

configured when you configure Envoy for the site). These probes contain information about the

requesting client and the resource that is being resolved. Site A also queries its local Envoy

agent (see Figure 68).

Figure 68 The selected Equalizer queries other Equalizers and its own servers in the geographic cluster

2. The Envoy agent at each site checks the availability of the requested resource (see Figure 69)

and sends a reply to Site A via GQP:

• If the resource is not available at the agent's site, the agent sends an error message to

Equalizer.

• If the resource is available at the agent’s site, the agent sends a message indicating the

availability of the resource back to site A via GQP.

Figure 69 The selected Equalizer receives availability and triangulation (latency) information

Note that if ICMP triangulation is enabled for the geocluster, the agent at a site where the

resource is available first sends an ICMP echo request (ping) to the requesting client. When the

echo reply from the client is received, the agent includes latency information in its reply to the

Envoy Site B

(West Coast USA)

Envoy Site A

(East Coast USA)

Internet

Envoy Site C

(Europe)

Client

(California, USA)