Brocade Communications Systems ServerIron ADX 12.4.00 Service Manual download pdf (Page 66)

54 ServerIron ADX Advanced Server Load Balancing Guide

53-1002435-01

Other TCS options

NOTE

If you configure the ServerIron ADX for Server Load Balancing (SLB) in addition to TCS, and the SLB

configuration provides load balancing for your cache servers, then content will be duplicated on the

cache servers as a result of the SLB predictor (load balancing metric). The SLB predictor works

differently from the TCS hash mechanism and assumes that content is duplicated across the

load-balanced server.

NOTE

Traffic controlled by policy-based caching on an individual server level is load balanced, whereas

traffic for the other cache servers is partitioned according to the hash feature. Refer to “Policy-based

caching” on page 90.

NOTE

If you use Content Aware Cache Switching (CSW in a TCS environment), URL string hashing is used

to select a cache server within a server group. Content duplication is minimized because requests

for cached content always go to the same cache server. Refer to “Active-standby TCS” on page 113

for more information.

Distribution algorithm

When a cache group contains multiple cache servers, the ServerIron ADX distributes traffic across

the caches. The ServerIron ADX distributes the traffic using a hashing feature. The hashing feature

uses a source hash mask and a destination hash mask for each cache group. The ServerIron ADX

maintains a separate hash table for each cache group.

The masks determine how much of the source and destination IP addresses are used by the hash

function to select a cache server. The ServerIron ADX uses the following hash masks by default:

For IPv4

• Destination Hash Mask:255.255.255.0

• Source Hash Mask:0.0.0.0

In the default hash mask, the first three octets of the destination address are significant and the

source address is not significant. Therefore, traffic addressed to any of the addresses in a Class-C

subnet always goes to the same cache server, regardless of the source address.

The ServerIron ADX uses the following algorithm for distributing traffic among the cache servers:

• "AND" the destination IPv4 address and destination IPv4 mask to get d1.d2.d3.d4.

• "AND" the source IPv6 address and source IPv6 mask to get s1.s2.s3.s4.

• Add each of the 1-byte values together sequentually: d1 + d2 +d3 +d4 + s1 + s2 +s3 +s4. This

yields a 1-byte value that is used as the hash value.

• This 1-byte hash value is used to map to an entry in the hash table. Each entry maps to an

active cache server.

For IPv6

• Destination Hash Mask:ffff:ffff:ffff:ffff:: (/64)

• Source Hash Mask::: (/0)

The ServerIron ADX uses the following algorithm for distributing traffic among the cache servers:

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Brocade Communications Systems ServerIron ADX 12.4.00 Service Manual Page 66