Brocade Communications Systems ServerIron ADX 12.4.00 - Manual (Page 115)

ServerIron ADX Global Server Load Balancing Guide 103
53-1002437-01
Enabling DNS request logging
1
Support for the RTT metric
When GSLB ran on the MP, the controller cached an RTT update only if that particular IP address
had made a DNS query earlier. This was to eliminate unnecessary RTT entries in the controller's
local cache. When a client made a DNS request, the controller cached the client’s prefix, as well as
the hostname it queried, in its local cache for a period of time, two minutes by default. The
controller stored the RTT update from the GSLB agent for a client network only if the client had
previously requested a domain name.
This behavior cannot be carried over to multiple CPUs because the BP that serves the DNS request
has to notify the other CPUs about the client’s request. The other CPUs can then cache the RTT
update, being well aware that a client from that network had made a DNS query already. This
means each DNS query would result in an IPC message, which is not acceptable for performance
reasons.
The client prefix entry is created when a site sends an RTT update for the client network. The cache
entry has a default age value of two minutes, which is refreshed each time a client from that
network makes a DNS query, or if a site sends an RTT update for that client's network. In addition,
the RTT cache organization was changed to become domain-name independent. Each client prefix
points to a flat table consisting of GSLB sites against the client’s RTT to the site. This is used to
determine which IP address is best for a client by finding the site that is closest to the client, based
on the RTT table.
This new design eliminates the limitation of storing only up to four proximity entries per domain
name. Now as many RTT entries can be stored as there are sites configured on the controller.
The output of the show gslb cache command has been changed to accommodate these RTT
changes. The following is sample output from the command. Note that the prefix entry has been
created due to an RTT update from a site, and also that RTT entries for this client network from 6
different sites are cached. Previously, only the best four RTT entries were cached, no matter how
many sites sent the updates.
ServerIronADX# show gslb cache 212.12.12.2

prefix length = 20, prefix = 212.12.0.0, region = EUROPE

prefix source = rtt-update,

site = local, ServerIron ADX = slb1(192.168.28.15), rtt = 3 (x100 usec)

site = client, ServerIron ADX = slb1(192.9.1.1), rtt = 4 (x100 usec)

site = remote6, ServerIron ADX = slb1(100.86.6.1), rtt = 4 (x100 usec)

site = remote7, ServerIron ADX = slb1(192.168.7.1), rtt = 6 (x100 usec)

site = remote8, ServerIron ADX = slb1(192.186.2.1), rtt = 12 (x100 usec)

site = remote9, ServerIron ADX = slb1(192.19.3.1), rtt = 8 (x100 usec)
TABLE 8 GSLB request information
This field... Displays...
User.Info The management IP address of the GSLB ServerIron ADX.
src-ip The IP address of the client that sent the DNS request.
best-ip The IP address selected by the GSLB ServerIron ADX as the best site.
Host The host application requested by the client.
Zone The zone name requested by the client.
Metric The GSLB metric according to which the site was selected as the best
site.