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Neil Stewart

Cisco Global Site Selector


Looking at the datasheet for the Cisco ACE GSS 4492R GSS device, under Global Traffic Management

" The Cisco GSS 4492R can be deployed as a standalone global traffic manager that globally load balances client requests across distributed data centers using network performance metrics such as content use, round-trip time (RTT) between client and the closest data center, routing topology, and any device performance values that are available through SNMP."

The part that interrests me is the RTT between client and closest data center. Looking at the config guide and other documentation I can see how make balancing decisions based on the client DNS server and find nothing based on actual client.

So the question - Is it possible to make balancing decisions based on round-trip time (RTT) between the actual client and the closest data center.

Sean Merrow

Hi Neil,

The feature you are referring to is Network Proximity.  The documentation could be a bit confusing because the "client" is relative.  To you and me, the client is the person (or application) making the original DNS request.  To the GSS, the client is that person's (or application's) local D-Proxy (DNS server).

When an application makes a DNS request to it's local D-Proxy, the D-Proxy will then attempt to resolve the request, but will source the request with it's own IP address, not the actual client's.  Therefore, by the time the request reaches the GSS, the GSS has no information on the original "client" or application that originated the DNS request.  It only knows the source IP address of the requesting D-Proxy and the domain it is requesting resolution for.  So to answer your question, no, the GSS cannot make a load balancing decision based on RTT between actual "client" and data center because it does not have sufficient data to make such a decision.

In most cases, each actual client will be using a D-Proxy that is local to them, so the effect is the same as what you are asking for.  But if the D-Proxy is remote to the actual client, then you could get unexpected results.

Hope this helps,