Technical data

ServerIron ADX Advanced Server Load Balancing Guide 43
53-1002435-03
Other transparent cache switching options
2
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 124 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.
For IPv4
The ServerIron ADX uses the following hash masks by default for IPv4 addresses:
• 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
sub-net 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 sequentially: 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
The ServerIron ADX uses the following hash masks by default for IPv6 addresses:
• 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:
• "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.