The IPFE (IP Front End) is a packet-based load balancer that makes a large DSR cluster accessible to incoming connections through a minimal number of IP addresses. These incoming connections can be TCP, unihomed SCTP, or multihomed SCTP. The IPFE distributes these connections among a list of target IP addresses by forwarding incoming packets. The list is called the Target Set IP List, and an outward-facing IP address is called a Target Set Address (TSA). A packet arriving at the IPFE and destined for the TSA is forwarded to an address in the Target Set IP List.
There can be as many as 16 IP addresses in the Target Set IP List and thus the IPFE may distribute traffic among as many as 16 physical or virtual application servers. Each server in the Target Set IP List can have a weighting indicating that the IPFE should apportion more or fewer connections to that server. The load balancing algorithm for apportioning connections is also configurable through a number of settings. The TSA, Target Set IP List, weighting, and load balancing algorithm settings are together called a Target Set. There can be as many as 32 independent Target Sets configured on one IPFE.
The IPFE neither interprets nor modifies anything in the TCP or SCTP payload. The IPFE also does not maintain TCP or SCTP state, but keeps sufficient state to route all packets for a particular session to the same application server.
Return traffic from the application server to the client (both TCP and SCTP) does not pass through the IPFE, but routes directly to the gateway.