BROCADE IP PRIMER

Console49F Link 50F1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47Power1F 2F 3F 4F2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48Co ns ol ePwrCC U1 PU 2 PU 3TxActRxActActi ve1 2 3 4 5 6 7 8 9 1 0 1 1 12 1 3 14 1 5 1 6J -F16GCJ-F16GCServerIron 850J -F16GCJ -F16GCJ-F16GCJ -F16GCJ -F16GCThe Health CheckWith the loopback in place the server will believe that the packet belongs to it,process the request, and send the reply directly to the client. Because of theloopback address, it will use the VIP address as the source IP address of thereply. To the client, it would appear that it has had a communication with theVIP, as the response would appear to have come from the VIP.sourceclient IPclient MACINTERNETdestinationVIPVIP MAC2 M M S W1 2 3 4 5 6 7 8 9 1 0 1 1 12 1 3 14 1 5 1 61 2 3 4 5 6 7 8 9 1 0 1 1 12 1 3 14 1 5 1 61 2 3 4 5 6 7 8 9 1 0 1 1 12 1 3 14 1 5 1 61 2 3 4 5 6 7 8 9 1 0 1 1 12 1 3 14 1 5 1 61 2 3 4 5 6 7 8 9 1 0 1 1 12 1 3 14 1 5 1 61 2 3 4 5 6 7 8 9 1 0 1 1 12 1 3 14 1 5 1 6sourcedestinationclient IPVIPloadbalance MAC server MACdestinationclient IPclient MACsourceVIPserver MACloopback: VIPWith Direct Server Return, the request comes into the load balancer, gets forwardedto the server, and the server replies directly to the client (not throughthe load balancer). This allows for the load balancer's bandwidth to the coreinfrastructure to be only used for incoming traffic (which is typically the smalleramount of data), and the servers can use their individual bandwidth for thereply (the greater amount of traffic).The Health CheckIf the load balancer is going to share incoming traffic with several servers, itneeds to be aware of which servers may or may not be active. If a server locksup, loses power, or has an application crash, the load balancer needs to know.If it doesn't, it could end up continuing to hand off traffic to a dead server. Howdoes the load balancer know? It knows because of the health check.A health check is a way to check on a server to see if it's functioning. It's kindof like the load balancer routinely saying, “Hey server, are you there? Are youokay? Do you feel alright? Could you handle any traffic if I were to send someyour way?” It's a check to verify the health of the server. The load balancermust check the health of every server it is load balancing.Some documentation refers to an “active health check.” This is so named, asthe load balancer is actively (not passively) checking on the health of its servers.It's configured to verify the servers' health above and beyond simplydefining the servers' existence. An active health check can be categorized inone of two ways: initialization and periodic. An initialization health check isperformed on a host when it is configured in the load balancer. Periodic healthchecks are those that are performed at repeating intervals to verify the statusof the server.Brocade IP Primer 103