Cisco Cisco IOS Software Release 12.2(18)SXF
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IOS Server Load Balancing Feature in IOS Release 12.2(18)SXF7
Features
Dynamic Feedback Protocol for IOS SLB
With IOS SLB Dynamic Feedback Protocol (DFP) support, a DFP manager in a load-balancing
environment can initiate a TCP connection with a DFP agent. Thereafter, the DFP agent collects status
information from one or more real host servers, converts the information to relative weights, and reports
the weights to the DFP manager. The DFP manager factors in the weights when load balancing the real
servers. In addition to reporting at user-defined intervals, the DFP agent sends an early report if there is
a sudden change in a real server’s status.
environment can initiate a TCP connection with a DFP agent. Thereafter, the DFP agent collects status
information from one or more real host servers, converts the information to relative weights, and reports
the weights to the DFP manager. The DFP manager factors in the weights when load balancing the real
servers. In addition to reporting at user-defined intervals, the DFP agent sends an early report if there is
a sudden change in a real server’s status.
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.
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.
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.
and GPRS) at the same time.
See the following sections for more information:
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DFP and GPRS Load Balancing
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:
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:
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.
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.
DFP and the Home Agent Director
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:
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
(cpu-utilization + memory-utilization)/32 * maximum-DFP-weight = reported-weight
The maximum-number-of-bindings is 235,000. The maximum-DFP-weight is 24.