Technical data

48 Brocade ServerIron ADX Advanced Server Load Balancing Guide
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Other transparent cache switching options
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The ServerIron ADX uses the following algorithm for distributing traffic among the cache servers:
• "AND" the destination IPv6 address and destination IPv6 mask to get 16 1-byte values: d1, d2
... d15, d16
• "AND" the source IP address and source IP mask to get 16 1-byte values: s1, s2 ... s15, s16
• Add each of the 1-byte values together sequentially: d1 + d2 + ...+ d15 + d16 + s1 + s2 + ... +
s15 + s16. 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.
The ServerIron ADX contains 256 hash slots. If you do not assign weights to the cache servers
(refer to “Setting the cache server weight” on page 65), the software divides the hash slots evenly
among the cache servers. If you assign differing weights to the cache servers, the software assigns
hash slots to the cache servers based on the ratios of their relative weights.
The hashing feature allows the switch to spread the traffic across the caches and minimizes
duplicate data on the cache servers.
If all the cache servers become unavailable, traffic flows across the switch at Layer 2 and users go
directly out to the Internet. The ServerIron ADX does not drop the traffic.
To change the hash mask, use the following command.
For IPv4
ServerIron(config)#server cache-group 1
ServerIron(config-tc-1)#hash-mask 255.255.255.0 255.255.0.0
For IPv6
ServerIron(config)#server cache-group 1
ServerIron(config-tc-1)#hash-mask ffff:ffff:ffff:ffff:: ffff:ffff:ffff::
Syntax: hash-mask { IPv4-destination-mask IPv4-source-mask | IPv6-destination-mask
IPv6-source-mask }
The IPv4-destination-mask IPv4-source-mask variables specify the IPv4 destination and source
masks to be used for the distribution algorithm.
The IPv6-destination-mask IPv6-source-mask variables specify the IPv6 destination and source
masks to be used for the distribution algorithm.
Table 4 shows other examples of how the hash masks work.
TABLE 4 Example TCS hash masks (IPv4+IPv6)
Destination mask Source mask Destination IP address Source IP address Cache server
255.255.255.0 0.0.0.0 10.24.32.12 Any C1
10.24.32.210 Any C1
10.24.33.210 Any C2
10.24.34.210 Any C3
255.255.255.192 0.0.0.0 10.24.32.12 Any C1
10.24.32.70 Any C2
10.24.32.190 Any C3