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the two ISPs.
Figure 4.5. A Route Load Balancing Scenario
We first need to define two routes to these two ISPs in the main routing table as shown below:
Route No. Interface Destination Gateway Metric
1 WAN1 all-nets GW1 100
2 WAN2 all-nets GW2 100
We will not use the spillover algorithm in this example so the routing metric for both routes should
be the same, in this case a value of 100 is selected (the all-nets route metric must always be greater
than other metrics).
By using the Destination RLB algorithm we can ensure that clients communicate with a particular
server using the same route and therefore the same source IP address. If NAT was being used for the
client communication, the IP address seen by the server would be WAN1 or WAN2.
Example 4.6. Setting Up RLB
In this example, the details of the RLB scenario described above will be implemented. The assumption is made
that the various IP address book objects needed have already been defined. The IP objects WAN1 and WAN2
represent the interfaces that connect to the two ISPs and the IP objects GW1 and GW2 represent the IP
addresses of the gateways at the two ISPs.
Step 1. Set up the routes in the main routing table
Step 2. Create an RLB Instance object
A Route Load Balancing Instance object is now created which uses the Destination algorithm will be selected to
achieve stickiness so the server always sees the same source IP address (WAN1 or WAN2) from a single client.
4.4. Route Load Balancing Chapter 4. Routing
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