BROCADE IP PRIMER

Configuring Direct Server Return (DSR)Configuring Direct Server Return (DSR)Once again, let's reflect on what we learned in Chapter 3. Direct Server Return(DSR) is an alternate solution to the problem of not having your real serversdirectly connected to the load balancer. In this scenario, the ServerIron passestraffic to the real server, and the real server responds directly back to the client(without the ServerIron ever seeing the return traffic). How is it able to dothis?For DSR to work, on each real server, you must have a loopback address configured.This loopback address must be the exact same IP address as the VIP.You also must make sure that your real server does not answer ARP requestsfor this address. This process is different for every real server's operating system.For help, consult Brocade's web site (http://www.brocade.com/).Once the loopback address is configured, the ServerIron, when it receives anincoming packet for the VIP, changes only the destination MAC address. Itchanges the address to be the MAC address of the real server it wishes tosend to. When the real server receives the packet, it sees that it is destined forthe VIP address. Because the real server has a loopback with the same IPaddress as the VIP, it knows to accept the packet. In addition, since the packetwas received to that address, the real server will reply as having come fromthat address. To the end user, it looks as if they have communicated with onehost.To configure the ServerIron, there are two more steps. First, you need to configurea “source-ip”, so that the ServerIron will be able to reach the remoteserver for health checks and to pass traffic. Remember, in DSR, the ServerIrononly changes the destination MAC address. If it cannot reach the real server inthe same broadcast domain, the ServerIron is not going to be able to pass traffic.This means that the ServerIron is going to need at least one physicalinterface that is in the same VLAN as the real servers. The “source-ip” is configuredthis way:SLB-ServerIron#conf tSLB-ServerIron(config)#server source-ip 10.20.30.3255.255.255.0 10.20.30.1Finally, enable DSR in the virtual server. This function is unique to the virtualserver. In fact, it's unique to a specific port on the virtual server. Here's anexample:SLB-ServerIron#conf tSLB-ServerIron(config)#server virtual-name www 1.2.3.4SLB-ServerIron(config-vs-www)#port httpSLB-ServerIron(config-vs-www)#port http dsrSLB-ServerIron(config-vs-www)#predictor round-robinSLB-ServerIron(config-vs-www)#bind http rs1 httpSLB-ServerIron(config-vs-www)#bind http rs2 httpBrocade IP Primer 343