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Chapter 14 Load Balancing in the P333R-LB
14 Avaya P333R-LB User’s Guide
Figure 14.3 Hash Metric - Loss of Persistency
When Firewall 2 is removed from the group, the list of available firewalls is
readjusted, causing a lack of persistency. However, if Firewall 2 becomes
operational again, the list of available firewalls is restored to its original order, and
persistency is recovered, making Hash a predictable metric.
MinMiss Hash
The metric parameter for MinMiss Hash is: Source IP, Destination IP.
MinMiss Hash distributes sessions to firewalls in the same way as the Hash metric.
However, MinMiss Hash sustains persistency even when a server is removed from
the firewall group. When a firewall fails or is removed, the positions of the other
firewalls in the list do not change. Instead, the remaining firewalls are redistributed
to the list entries freed by the failing firewall. The following figure illustrates how
persistency is maintained even though a firewall becomes non-operational.
Figure 14.4 MinMiss Hash Metric - Persistency Sustained
When Firewall 2 is removed from the group, the list of available firewalls is not
readjusted. Only the list entries that are now empty are replaced with other
available firewalls. Therefore, persistency is sustained for all available firewalls. If
Firewall 2 becomes operational again, the list of available firewalls is recalculated so
that the smallest number of firewalls is affected. However, the list of firewalls is not
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Loss of
Persistency
Hash Function
pointing to Firewall 4
The same
Hash Function
pointing to Firewall 1
List of available Firewalls
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Persistency
Kept
The same
Hash Function still
pointing to Firewall 4
List of available Firewalls
Hash Function
pointing to Firewall 4