BROCADE IP PRIMER

Chapter 18: Global Server Load Balancing (GSLB)Administrative PreferenceAdministrative Preference is kind of like Check 6.5. It's considered right beforeLeast Response. Administrative Preference is disabled by default. When it isenabled, all sites have a default administrative preference of 128. The preferencefor each site may be set at any number from 0 to 255. A higher numberindicates a higher GSLB preference.Why would you want to do this? Well, here are some good reasons:• You can temporarily disable a site without changing any other configurationpieces. Let's say, your site has a back-end database. The database atone site is becoming particularly congested (a situation that would notreveal itself in the other checks). Or let's say you were performing a scheduledmaintenance on a site. You could temporarily disable client access tothe site simply by setting a low administrative preference (say, 0).• Let's say you have a GSLB ServerIron that's also acting as the ServerIronfor one of the sites. You may want this ServerIron to deliberately preferitself. To do this, you could set the administrative preference to 255.Configuring GSLBTo configure GSLB, you need to start by making sure the ServerIron is able tohealth check to remote sites. You can do this by configuring a source-ip:SLB-ServerIron#conf tSLB-ServerIron(config)#server source-ip 123.1.2.3255.255.255.0 123.1.2.1Next, you define the ServerIron as a DNS proxy to your actual DNS servers.You'll recognize this setup from SLB:SLB-ServerIron#conf tSLB-ServerIron(config)#server real-name dns-server1123.1.2.11SLB-ServerIron(config-rs-dns-server1)#port dns proxySLB-ServerIron(config-rs-dns-server1)#server real-name dnsserver2123.1.2.12SLB-ServerIron(config-rs-dns-server2)#port dns proxySLB-ServerIron(config-rs-dns-server2)#exitSLB-ServerIron(config)#server virtual-name DNSProxy123.1.2.10SLB-ServerIron(config-vs-DNSProxy)#port dnsSLB-ServerIron(config-vs-DNSProxy)#bind dns dns-server1 dnsdns-server2 dnsIt's configured just like we're load balancing DNS servers with SLB, with oneimportant difference. In the real server configs, we used the words “port dnsproxy.” This indicates that we want the ServerIron to act as a DNS proxy for thereal servers. Now, the SLB rules for real servers apply here. If these DNS serversare not directly connected to the ServerIron, you'll need to use Source NAT(as the ServerIron is acting as a proxy, DSR would not work).396 Brocade IP Primer