HASH Carp Persistence

so how does it consistently map to the same pool member based on source ip? The hash value needs to be stored, correct?

key and pool member both are included in hash algorithm. the highest score will be chosen. so, the same pool member will always be picked as long as it is up.

3. Routing Function

  Once an agent has a Proxy Array Membership Table.  It uses a 
  mathematical hash function to determine which of the members of 
  the array should be the receptacle of a particular URL request.

  This routing function involves constructing n "scores" using a hash
  of the request URL plus a hash of each of the k proxies in the Proxy
  Array Membership Table.  

  Both the URL and the proxy names are hashed in order to minimize the
  disruption of target routes if a member of the target array can't
  be contacted.

  Hashes of the URL and proxy name are constructed using the algorithm
  described in 3.1 and combined using the algorithm described in 3.2.

3.4. Route Selection

  The "score" for a particular combination of URL plus proxy is its
  resultant value. Once the agent determines the scores of the 
  K proxies, it routes the URL query to the proxy with the highest 
  score.

Cache Array Routing Protocol v1.0