This MIB module in conjunction with the
CISCO-CASA-MIB, defines the SNMP management
information base for managing the Cisco Appliance
Services Architecture (CASA) Forwarding Agent.
The following is a set of definitions used in the
rest of the MIB.
CASA is a protocol allowing software entities (called
Appliances, examples are web caches, firewalls, load
balancers) to control the behavior of network hardware
devices (called Forwarding Agents, examples are
switches or routers) by providing a set of rules used
to handle network traffic.
A Network Appliance (referred to as an Appliance) is
any subsystem whose purpose is to provide a specific
additional value-added service to the network device,
and could be implemented as a standalone box, a line
card or processor card, or a software subsystem.
Examples of Network Appliances would include Load
Balancers, WebCaches, and Firewalls.
An Appliance tells Fowarding Agents how to handle
packets based on their source and destination IP
addresses and ports, and IP protocol fields. This set
of information is called an Affinity.
A Service Manager is an Appliance that requests
packet flows from Forwarding Agents through CASA.
A Real Server is a physical computing engine or part
of that physical computing engine that offers one or
more application services to a set of clients in the
A packet flow is a TCP connection or a sequence of UDP
packets between a client and a specific Real Server,
pertaining to a specific application. Flows are
represented by entries in the affinity cache tables.
The Service Manager requests packet flows from
Forwarding Agents by sending Affinities which contains
wildcards on some of the Affinity fields. Affinities
that contain wildcards in some of the fields are
called Wildcard Affinities. The Service Manager may
send the Forwarding Agent an Affinity containing
explicit values for each of the fields. These
Affinities are called Fixed Affinities.
Typically Wildcard Affinities are used to instruct the
Forwarding Agent to send packets received by the
Forwarding Agent, which match the Wildcard Affinity,
to the Service Manager. When the Service Manager
receives the matching packet, the Service Manager
typically will send the Forwarding Agent a Fixed
Affinity. The Forwarding Agent uses Fixed Affinities
to match packets coming from the network, execute any
processing required on that packet, and forward that
packet to a destination IP address (designated in the
Fixed Affinity) called the Dispatch Address.
When an IP packet arrives at the Forwarding Agent, the
Forwarding Agent attempts to match the packet with the
Fixed Affinities in the Fixed Affinity cache. If
there is no match, an attempt is made to match the
packet with the list of Wildcard Affinities. If there
is no match the packet is routed normally. If there is
a match with a Wildcard Affinity, the Forwarding Agent
sends the packet to the Service Manager who will send
the Forwarding Manager a Fixed Affinity which provides
information on how to process IP packets similar to
the one received by the Forwarding Agent. Processing
of such packets may include sending the packet to the
Service Manager. Such packets are called Interest
Packets. Alternatively a Tickle Packet may be sent to
the Service Manager which is an indication that a
matched packet has been received by the Forwarding
Reference:  Cisco Appliance Services Architecture
Diagram showing Forwarding Agents, Service Manager,
Real Server and clients.
______ ______ ______
(Real ) (Real ) (Real )
(Server) (Server) (Server)
(______) (______) (______)
| | |
+---------------+ | | |
|Service Manager|-+----------+--------------+ |
+---------------+ | | | | |
++---------+ ++---------+ ++---------+
| F. Agent | | F. Agent | | F. Agent |
+----------+ +----------+ +----------+
| | |
( N E T W O R K )