A Cisco CSS acts as a multilayer switch and performs FWLB as well as many other types of content processing. A CSS interface can carry a single VLAN or a trunk with multiple VLANs.
A CSS unit must be placed on each side of a firewall farm so that connections are load-balanced to the firewalls in each direction. Firewalls are defined individually rather than as a distinct firewall farm.
The CSS performs a route lookup on each inbound connection to determine the possible firewalls that can be used. The CSS then computes the exclusive OR (XOR) of the source and destination IP addresses as a hash value to select which firewall will receive the connection.
Keepalives (custom ICMP packets) are sent from one CSS ...