IP Load Balancing (LB) implements a generic mechanism that load balances all IP traffic, irrespective of the transport protocol. This feature inspects only the IP header and is completely transparent to upper layer protocols. IP LB is designed to be a stateless solution. That is, it does not track traffic flows and has no intelligence about connection establishment/termination.
Enable this feature at the virtual server configuration level. A virtual server is bound to a set of real servers for IP LB, and all IP traffic destined to the virtual server IP address will be load balanced across the real servers. The configuration or binding of virtual ports to real ports has no meaning in the context of IP LB, and all binding is at a server level (as opposed to the traditional binding of ports).
The load balancing scheme is based on a hash of the source IP address. Each virtual server is associated with a hash table (size 256) for IP LB. To begin with, the hash table is empty, and any client request will go through the server selection process (the only supported load balancing metric for IP LB is round-robin). After a server is selected, a reference to the server is placed in the hash bucket corresponding to the client IP address. All subsequent requests from that source IP address (or any other source IP hashing to the same hash bucket) will be directed to this real server, as long as the server is "healthy". In this way, the hash table is populated and is ensured that all packets originating from a specific client are load balanced to the same real server. Client persistence is implicit for IP LB.
Since this feature is completely hash based, it is essential that the state of the hash table always be consistent with the state of the real servers associated with the virtual server. For example, a hash bucket should not be pointing to a real server that is down due to health check. For this purpose, the ServerIron ADX identifies and handles the following cases:
If a VIP is enabled for IP load balancing, it cannot be enabled for regular load balancing. If a VIP is enabled for regular TCP/UDP load balancing, it cannot be enabled for IP load balancing. These two features are mutually exclusive.
Since IP LB is a stateless feature, it cannot operate in conjunction with any other Layer 4 features supported by the ServerIron ADX (such as syn proxy, ACLs, Transaction Rate Limiting, and so on). The reason is all other ServerIron ADX features are stateful and act on flows.
The way these mechanisms work remains the same as in previous releases, and IP LB does not mandate any change to these features. For maintaining persistence across a fail over, the IP LB hash table is synchronized to the peer ServerIron ADX. This sync is done only for hot standby and symmetric SLB setup, not for sym-active configuration. The reason is for sym-active, both the SIs can be taking traffic for the same virtual IP, and synchronizing the hash table to each device means overriding each device's hashing decision.
You can bind a real server to a virtual server for IP LB. The procedure of configuring virtual servers and configuring real servers remains the same as earlier releases.
To specify an optional list of IP protocols to load balance, enter commands such as the following:
To display load-balancing information, enter the following command:
The <vserver-name> parameter is the name of a virtual server.
