Cisco Cisco IOS Software Release 12.2(14)ZA
Features
7
Cisco IOS Release 12.2(14)ZA7
For example, assume a server farm comprised of real server ServerA with n = 3, ServerB with n = 1, and
ServerC with n = 2. The first three connections to the virtual server are assigned to ServerA, the fourth
connection to ServerB, and the fifth and sixth connections to ServerC.
ServerC with n = 2. The first three connections to the virtual server are assigned to ServerA, the fourth
connection to ServerB, and the fifth and sixth connections to ServerC.
Note
Assigning a weight of n=1 to all of the servers in the server farm configures the IOS SLB device to use
a simple round robin algorithm.
a simple round robin algorithm.
General packet radio service (GPRS) load balancing without GPRS Tunneling Protocol (GTP) cause
code inspection enabled requires the weighted round robin algorithm. A server farm that uses weighted
least connections can be bound to a virtual server providing GPRS load balancing without GTP cause
code inspection enabled, but you cannot place the virtual server INSERVICE. If you try to do so,
IOS SLB issues an error message.
code inspection enabled requires the weighted round robin algorithm. A server farm that uses weighted
least connections can be bound to a virtual server providing GPRS load balancing without GTP cause
code inspection enabled, but you cannot place the virtual server INSERVICE. If you try to do so,
IOS SLB issues an error message.
The Home Agent Director requires the weighted round robin algorithm. A server farm that uses weighted
least connections can be bound to a Home Agent Director virtual server, but you cannot place the virtual
server INSERVICE. If you try to do so, IOS SLB issues an error message.
least connections can be bound to a Home Agent Director virtual server, but you cannot place the virtual
server INSERVICE. If you try to do so, IOS SLB issues an error message.
Weighted Least Connections
The weighted least connections algorithm specifies that the next real server chosen from a server farm
for a new connection to the virtual server is the server with the fewest active connections. Each real
server is assigned a weight for this algorithm, also. When weights are assigned, the server with the fewest
connections is based on the number of active connections on each server, and on the relative capacity of
each server. The capacity of a given real server is calculated as the assigned weight of that server divided
by the sum of the assigned weights of all of the real servers associated with that virtual server, or
n
for a new connection to the virtual server is the server with the fewest active connections. Each real
server is assigned a weight for this algorithm, also. When weights are assigned, the server with the fewest
connections is based on the number of active connections on each server, and on the relative capacity of
each server. The capacity of a given real server is calculated as the assigned weight of that server divided
by the sum of the assigned weights of all of the real servers associated with that virtual server, or
n
1
/(n
1
+n
2
+n
3
...).
For example, assume a server farm comprised of real server ServerA with n = 3, ServerB with n = 1, and
ServerC with n = 2. ServerA would have a calculated capacity of 3/(3+1+2), or half of all active
connections on the virtual server, ServerB one-sixth of all active connections, and ServerC one-third of
all active connections. At any point in time, the next connection to the virtual server would be assigned
to the real server whose number of active connections is farthest below its calculated capacity.
ServerC with n = 2. ServerA would have a calculated capacity of 3/(3+1+2), or half of all active
connections on the virtual server, ServerB one-sixth of all active connections, and ServerC one-third of
all active connections. At any point in time, the next connection to the virtual server would be assigned
to the real server whose number of active connections is farthest below its calculated capacity.
Note
Assigning a weight of n=1 to all of the servers in the server farm configures the IOS SLB device to use
a simple least-connection algorithm.
a simple least-connection algorithm.
GPRS load balancing without GTP cause code inspection enabled does not support the weighted least
connections algorithm.
connections algorithm.
GPRS load balancing with GTP cause code inspection enabled does support the weighted least
connections algorithm.
connections algorithm.
The Home Agent Director does not support the weighted least connections algorithm.
Bind ID Support
The bind ID allows a single physical server to be bound to multiple virtual servers and report a different
weight for each one. Thus, the single real server is represented as multiple instances of itself, each having
a different bind ID. Dynamic Feedback Protocol (DFP) uses the bind ID to identify for which instance
of the real server a given weight is specified. The bind ID is needed only if you are using DFP.
weight for each one. Thus, the single real server is represented as multiple instances of itself, each having
a different bind ID. Dynamic Feedback Protocol (DFP) uses the bind ID to identify for which instance
of the real server a given weight is specified. The bind ID is needed only if you are using DFP.
GPRS load balancing and the Home Agent Director do not support bind IDs.