BROCADE IP PRIMER

ServerIronChapter 15: Server Load Balancing (SLB)Notice something significant about this picture? The real server never saw anytraffic. The ServerIron sent a TCP SYN/ACK on behalf of the real server. TheServerIron will wait (by default) eight seconds. If it doesn't see an ACK backfrom the client, it sends a TCP RST to the client, and clears the session. Thereal server is oblivious that any transaction has taken place.ClientSYN-Guard TMServerIronServerTCP SYNTCP SYN/ACKTCP ACKDataTCP SYNTCP SYN/ACKTCP ACKDataWith SYN-Guard enabled, this is how you would normally see the traffic comethrough. Notice that the three-way handshake is only handed off to the realserver when it has finished between the client and the ServerIron. TheServerIron is acting as a three-way handshake proxy. After the handshake iscompleted, traffic will pass through uninhibited for that session.To configure this feature, use the following command in the Global config:SLB-ServerIron#conf tSLB-ServerIron(config)#ip tcp syn-proxy 10This has now globally-enabled SYN-Guard and set the timer to 10 seconds.This is how long the ServerIron will wait, after having sent the TCP SYN/ACK, toterminate a session.For more information on current ServerIron protection features, please seeBrocade's web site (http://www.brocade.com/).PredictorsThe predictor is the method that the ServerIron uses to balance the loadacross the configured servers. When an incoming packet comes into theServerIron, it needs to make a decision as to which real server to forward thepacket to. The ServerIron provides several different methods to do this:• Least connections. This is the default predictor. This method looks at thecurrent number of connections that each real server has, and picks theone with the least number of connections to forward the next incomingpacket to. This method works well, if your real servers are all very similarin their capacity.332 Brocade IP Primer