Citrix NetScaler EE, Installation And Configuration Manual

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more equal number of remote users (not sites) per appliance, but at the expense of compression effectiveness.
(Compression is only effective when connections flow through the same appliances, and splitting traffic from the same
remote site between two or more local appliances interferes with this.)
Finally, for good load-balancing, each "one" bit in the address mask must be set to one on 50% of the remote addresses,
and set to zero on 50% of the remote addresses. This is not the case on all address bits, since in most WANs, the highest-
order network bits never change at all (such as the 10 in 10.x.x.x). Such bits must never be selected by the address mask.
In addition, many subnets are only sparsely populated. For example, if only 50 addresses are used in the subnet 10.1.2.0/24,
and they are assigned sequentially, the two higher-order host bits (representing the unused range of 10.1.2.64-10.1.2.255)
for this subnet never change, and if these two bits are included in the address mask, three-fourths of the buckets receive
no traffic.
Useful compromises between these two extremes can generally be found.
Follow these rules:
The number of ”one” bits in the address mask must allow at least as many combinations as there are WCCP caches in
the cluster. That is, if you have eight appliances, the address mask must contain at least three ”one” bits.
The ”one” bits in the address mask must each be inside the active address range for most of your remote subnets, or
they skew the load-balancing distribution.
The mask should split the address range of individual remote sites into as few pieces as possible, for best compression
performance.
If a remote appliance is faster than the local members of the WCCP cluster, the mask should be designed to divide its
traffic between multiple local appliances. For example, a 100 Mbps remote appliance should have its traffic split between
two 50 Mbps local appliances by setting a bit inside the remote appliance’s active address range.
The “one” bits in the mask are typically contiguous, but this is not required. They can be in any pattern.
Example Example: Suppose you set an address mask of 0x0000 0f00, which has four “one” bits. This defines a four-bit field that is
extracted from the IP address, yielding 16 possible results (16 buckets). These buckets are in turn assigned to the actual
WCCP caches in the WCCP cluster.
Address Address Masked Masked Address (mask = 0x0000 0f 00) Address (mask = 0x0000 0f 00) Bucket Bucket
10.0.0.5 0.0.0.0 0
10.0.1.128 0.0.1.0 1
155.0.2.55 0.0.2.0 2
253.100.255.2 0.0.15.0 15
10.0.15.1 0.0.15.0 15
Zero bits in the mask are ignored, and the “one” bits are used to define the extracted field. So if the mask is 0x10 10 10 10,
these widely separated “one” bits are extracted into a four-bit field, declaring 16 buckets and a bucket numbers in the
range of 0-15.
If the mask value is set to zero, a default value of 0x00 00 0f 00 is used.