Q: When using proximity-based Global Server Load Balancing (GSLB), can there be significant discrepancies caused by using the Local Domain Name System (LDNS) to determine where a client is rather than the client itself?
A: Yes. However, the difficulty is that when clients make Domain Name System (DNS) requests, they typically do so to their LDNS server. Most LDNS servers are configured to do recursive lookups, which means the NetScaler system never sees the actual client IP address, only the LDNS address.
While there are known exceptions (AOL being the typically cited case since all users call on the same set of LDNS servers in Reston, Virginia, regardless of their location), the LDNS method works well for most users.
Note: The AOL citation is actually invalid. Because AOL's HTTP proxy farm makes all HTTP requests come out of Reston, Virginia, having the LDNS servers in Reston produces the fastest response times for AOL users.
