Technical data

54 ServerIron ADX Advanced Server Load Balancing Guide
53-1002435-03
Other transparent cache switching options
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ServerIronADX(config)# server cache-group 1
ServerIronADX(config-tc-1)# source-nat
ServerIronADX(config-tc-1)# dest-nat
These commands configure a source IP address at the global CONFIG level of the CLI, then change
the CLI to the cache group configuration level and enable source NAT and destination NAT. Source
NAT configures the ServerIron ADX to change the source IP address in a client query from the
client’s IP address to configured source IP address. Destination NAT configures the ServerIron ADX
to change the destination IP address of the client’s request to the IP address of the cache server.
Syntax: [no] source-ip <ip-addr> <network-mask> <default-gateway>
NOTE
The gateway parameter is required. If you do not want to specify a gateway, enter "0.0.0.0".
Syntax: [no] source-nat
To enable source NAT on a specific cache server instead of at the cache group configuration level
for all cache servers, enter commands such as the following:
ServerIronADX(config)# server cache-name C1
ServerIronADX(config-rs-C1)# source-nat
ServerIronADX(config-rs-C1)# dest-nat
The commands in this example enable source NAT and destination NAT on cache server C1 only.
This example assumes that the source IP address also is configured as shown in the previous
example.
NOTE
FTP is not supported when source NAT is configured.
Increasing the TCS hash bucket count
The ServerIron ADX supports 256 hash buckets by default. If you do not assign weights to the
cache servers, the software divides the hash buckets evenly among the cache servers. With the
default hash bucket count of 256, there is a limitation of traffic distribution. In a setup with a large
number of cache servers, if one of the cache servers fails, then their remaining cache servers may
get hit by traffic spikes due to limited load balancing by hash buckets.
Consider an example where there are 64 cache servers within one cache group (CS1 through
CS64). Because there are 256 buckets, each server is assigned four buckets (256 / 64 = 4). If one
cache server (CS1), goes down, the four buckets assigned to CS1 are re-assigned to cache servers
“CS2-CS5”. Consequently, “CS2-CS5” have five buckets each while CS6 through CS64 still have
four buckets. This means that the original traffic handled by the cache server going down is not
distributed evenly among the rest of the cache servers. The traffic on CS2 through CS5 increases
by 25 percent ([ 5 - 4] / 4= 25%).
You can increase the TCS hash bucket count to a higher number to ensure a more reasonable
distribution of excess traffic among remaining cache servers when a cache server goes down.
Using the previous example in which there are 64 cache servers(CS1-CS64) you can upgrade the
TCS hash bucket count to 8192. Because 8192 / 64 = 128, each server is now assigned 128
buckets. If one cache server (CS1) goes down, then the 128 buckets assigned to CS1 are
re-assigned to the other 63 servers. In this situation, CS2 and CS3 get three additional buckets