Load Balancing Metrics For Transparent Routing Fwlb; Hash; Figure 7.3 Hash Metric - Loss Of Persistency - Avaya P333R-LB User Manual

Chapter 7 Firewall Load Balancing

Load Balancing Metrics for Transparent Routing FWLB

There are different methods, or metrics, that the P333R-LB can use to distribute
traffic among multiple firewalls. These metrics tell the P333R-LB which server
should receive the next session.
Transparent Routing FWLB uses the following metrics:
•

Hash.

• MinMiss Hash.
Each load balancing metric can be performed on one of the following metric
parameters:
• SRC IP (source IP address).
• DST IP (destination IP address).
• SRC and DST IP (a combination of source and destination IP addresses).
Hash
Hash is the default metric for FWLB, and the default metric parameter for
Transparent FWLB Hash is: Source IP, Destination IP.
Using the Hash metric, sessions are distributed through firewalls using a
predefined mathematical hash function. This hash function is created by a hash
value, performed on a specific parameter. The source and destination IP addresses
are used as the hash function input.
P333R-LB creates a list of all the currently available firewalls. The result of the hash
function is used to select a firewall from the list. Specific source and destination IP
addresses always produce the same hash function, providing natural persistency.
If a firewall is added or removed to the group, the persistency will be broken. This
occurs, since the order of the firewalls in the list changes, but the hash still points to
the same list entries. The following figure illustrates how a loss of persistency occurs
when a firewall becomes non-operational.
Figure 7.3
Hash Function
pointing to Firewall 4
List of available Firewalls
202
Hash Metric - Loss of Persistency
1 1
2 2
Firewall 2
3 3
4 4
1 1
2 2
3 3
Server Server
4 4
1 1
2 2
3 3
1 1
3 3
4 4
1 1
3 3
4 4
1 1
The same
3 3
Hash Function
4 4
pointing to Firewall 1
1 1
3 3
Avaya P333R-LB User's Guide
Loss of
Persistency