Cisco Cisco IOS Software Release 12.2(18)SXF

The weights calculated by DFP override the static weights you define using the weight command in 
server farm configuration mode. If DFP is removed from the network, IOS SLB reverts to the static 
weights.

You can define IOS SLB as a DFP manager, as a DFP agent for another DFP manager, or as both at the 
same time. In such a configuration, IOS SLB sends periodic reports to the other DFP manager, which 
uses the information to choose the best server farm for each new connection request. IOS SLB then uses 
the same information to choose the best real server within the chosen server farm.

DFP also supports the use of multiple DFP agents from different client subsystems (such as IOS SLB 
and GPRS) at the same time.

See the following sections for more information:

In GPRS load balancing, you can define IOS SLB as a DFP manager and define a DFP agent on each 
GGSN in the server farm. Thereafter, the DFP agent can report the weights of the GGSNs. The DFP 
agents calculate the weight of each GGSN based on CPU utilization, processor memory, and the 
maximum number of Packet Data Protocol (PDP) contexts (mobile sessions) that can be activated for each 
GGSN. As a first approximation, DFP calculates the weight as the number of existing PDP contexts 
divided by the maximum allowed PDP contexts:

(existing PDP contexts)/(maximum PDP contexts)

Maximum PDP contexts are specified using the gprs maximum-pdp-context-allowed command, 
which defaults to 10,000 PDP contexts. If you accept the default value, DFP might calculate a very low 
weight for the GGSN:

(existing PDP contexts)/10000 = Low GGSN weight

Keep this calculation in mind when specifying maximum PDP contexts using the 
gprs maximum-pdp-context-allowed command. For example, Cisco 7200 series routers acting as 
GGSNs are often configured with a maximum of 45,000 PDP contexts.

For the Home Agent Director, you can define IOS SLB as a DFP manager and define a DFP agent on 
each home agent in the server farm, and the DFP agent can report the weights of the home agents. The 
DFP agents calculate the weight of each home agent based on CPU utilization, processor memory, and 
the maximum number of bindings that can be activated for each home agent:

(maximum-number-of-bindings - current-number-of-bindings)/maximum-number-of-bindings * 
(cpu-utilization + memory-utilization)/32 * maximum-DFP-weight = reported-weight

To set the maximum-number-of-bindings, use the ip mobile home-agent max-binding command. To set 
the maximum-DFP-weight sent by the home agent to IOS SLB, use the ip mobile home-agent 
dfp-max-weight command. For detailed information about these Mobile IP commands, refer to the 
Cisco Mobile Wireless Home Agent Release 2.0 feature module.

This feature enables a GGSN to notify IOS SLB when certain conditions occur. The notifications enable 
IOS SLB to make intelligent decisions, which in turn improves GPRS load balancing and failure 
detection.