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Consistent Hash IP (chi) SLB Definition
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This SLB method  use the CHI algorithm to maps the client requests to servers by hashing the source IPs of the requests.

slb group method <group_name > chi [hash_bits] 

[hash_bits]  - optional field controls how many bits of the source IP are used in generating the
hash. The value of <hash_bits> can be any number between 0 and 32 inclusive, with a default of
32.

Consistent Hash IP (CHI):
This algorithm provides two key advantages that are sort of a combination of Hash IP and Persistent IP:
1. When a real service in the group goes down, clients who were not mapped to the down real service are unaffected (Persistent IP). That means the existing persistency between clients and available servers will not be disrupted.
2. Two or more Array boxes in a clustering environment with the exact same group configuration will have identical hash tables. In a failover situation, a given client will map to the same real service on the backup Array that the same client mapped to on the master Array.
 
In the event that a real service goes down, the entries in the group's hash table which are assigned to the down real service will be set to NULL.
When a source IP is hashed to one of these "null" buckets at some position in the table, the source IP will be re-hashed to another position. 
 
When a real service in the group comes back up, the original mapping is restored.
 
NOTE: If real services are added or removed from the group by the administrator, the entire table will be recomputed, thus breaking persistency for all existing users.


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