A CCESS GATEWAYIntroduction 29Multiple Unit ClusteringIn the recent past, it was necessary to segment the network to serve a number of subscribersthat exceed the user count on a Nomadix gateway. Now with clustering all subscribers can beon the same segment, as the subscribers are distributed across multiple gateways. A largenumber of subscribers can be distributed to as many as 250 gateways, thus providing a designcapacity of 1 million subscribers being served.One can scale the cluster up and down just by adding gateways or removing gateways.Remember that a subscriber and the subscriber’s MAC address are positioned in a specificgateway, so changing the number of gateways will require the gateways to reconfigure, andtheir current subscriber table updated. If a prepaid subscriber exists in a radius orauthentication file, this prepayment will be lost. It is recommended that prepayment situationsshould be avoided.The cluster will distribute the subscribers MAC addresses according to a modulus calculationbased on the last three bytes of the MAC address of the subscriber. The result will determinewhich gateway will support that MAC address while the other gateways ignore the traffic forthe MAC.With the 8.3 release, there is currently no failover in support of clustering. This will beaddressed in later releases.The following other NSE features are not compatible with clustering: Proxy ARP for device Routed subscribers Intra-port communicationIdentifying the Resident Gateway in a Cluster EnvironmentTo diagnose device connection problems in a cluster environment, you must identify theresident gateway. For a given MAC address, you can determine the gateway as follows. Youwill need the last three bytes of the device MAC address and the total number of gateways.Convert the hex bytes to decimal:1. Using the Windows Calculator in programmer mode2. In hex mode, input the last three bytes of the MAC address3. Convert to decimal by using that function on the calculatorThe resident gateway is the (decimal bytes) modulus (the total number of gateways), plus 1.
