BROCADE IP PRIMER

ConsoleNETWORKSFastIron Edge X44849F 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-F16GCChapter 5: Load Balancing Basicsdestinationclient IPINTERNETsourceclient IPsourceVIPdestinationVIPdestinationloadbalance IP2 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 6sourceloadbalance IPsourceserver IPdestinationserverIPSource NAT still allows the load balancer to keep an intimate record of datapassing, active sessions, and so on, because all traffic is still coming into andgoing out of the load balancer.Direct Server Return (DSR)Okay, I've got a ton of servers (too many to physically connect to my load balancer),but what if I'm passing a really large amount of traffic? My loadbalancer, for example, only has a 100 Mbps connection to my core switch.That means that if all traffic is coming into and out of the load balancer (usingSource NAT), I'm only going to get 100 Mbps worth of throughput. If I have1,000 servers, I'm still ultimately limited by that 100 Mbps throughput. I needmuch more than that for my environment! Enter Direct Server Return (DSR).Remember that if we use SLB (when your servers are not physically connectedto the load balancer, and the network path does not route all traffic into andout of the load balancer) that it is the reply that is the problem. One way tosolve this problem is with Source NAT. The disadvantage there is that all trafficis still going through the load balancer. If our load balancer's throughput to thecore infrastructure is low (as in our example), this would be undesirable.DSR presents another solution to the problem. The load balancer receives theincoming request, but this time, it only changes the destination MAC address,not the IP address, and forwards the packet to the chosen server.But why would the server accept the packet? It's not addressed to it. Or is it?For DSR to work, a loopback address must be configured on all load-balancedservers. This address is not assigned to a specific NIC. Think of the loopbackaddress as the address of the server itself. You may be familiar with thedefault loopback address of 127.0.0.1. Each server must be configured withan additional loopback address, which will be the same address as the VIP.Special precautions must be made so that the server configured with this loopbackaddress will not advertise this address (in ARP messages), nor will itanswer ARP broadcasts (otherwise, it would conflict with the load balancer).Consult Brocade's website (http://www.brocade.com/) for further details onconfiguring a DSR loopback IP address to your specific operating system.102 Brocade IP Primer