D-Link 800 - DFL 800 - Security Appliance, User Manual, Page: 142 / 469

3. If more than one matching route is found then RLB is used to choose which one to use. This is
done according to which algorithm is selected in the table's RLB Instance object:
• Round Robin
Successive routes are chosen from the matching routes in a "round robin" fashion provided
that the metric of the routes is the same. This results in route lookups being spread evenly
across matching routes with same metric. If the matching routes have unequal metrics then
routes with lower metrics are selected more often and in proportion to the relative values of
all metrics (this is explained further below).
Figure 4.3. The RLB Round Robin Algorithm
• Destination
This is similar to Round Robin but provides "stickiness" so that unique destination IP
addresses always get the same route from a lookup. The importance of this is that it means
that a particular destination application can see all traffic coming from the same source IP
address.
• Spillover
Spillover is not similar to the previous algorithms. With spillover, the first matching route's
interface is repeatedly used until the Spillover Limits of that route's interface are
continuously exceeded for the Hold Timer number of seconds.
Once this happens, the next matching route is then chosen. The Spillover Limits for an
interface are set in the RLB Algorithm Settings along with the Hold Timer number of
seconds (the default is 30 seconds) for the interface.
When the traffic passing through the original route's interface falls below the Spillover
Limits continuously for the Hold Timer number of seconds, route lookups will then revert
back to the original route and its associated interface.
Figure 4.4. The RLB Spillover Algorithm
4.4. Route Load Balancing Chapter 4. Routing
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