WAN Link Fault Tolerance
Load Balancing & Fault Tolerance
Load Balancing & Fault Tolerance
WAN Link Fault Tolerance
With the rapid proliferation and decreasing prices of broadband solutions, more and more small and medium
enterprises are opting for the use of multiple WAN links from various ISPs. The benefits include:
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Single link failure does not result in a total loss of internet connectivity, thus WAN reliability increases.
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Traffic can be evenly dispersed across multiple WAN links, resulting in increased efficiency and improved
performance of bandwidth.
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Multiple WAN links for fault tolerance and load balancing has two advantages:
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The outbound traffic, i.e. traffic originating from LAN traveling outwards, can be load-balanced across multiple
WAN links. This is Auto Routing.
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Traffic from the WAN, i.e. traffic originating from WAN traveling towards the LAN, can be load-balanced across
multiple WAN links. This is Multihoming.
Load Balancing Algorithms
FortiWAN offers seven types of auto routing algorithms for administrators to select the best policy to match their
environment. It's based to sessions for Auto Routing to distribute traffic among multiple WAN links. All the packets of a
session are routed to the WAN link that the session is distributed to. Sessions are transferred via different WAN links
according to algorithm, but packets of a session are transferred via one WAN link. All the routing policies (except the
fixed one) will ONLY use working WAN links and by-pass the failed ones.
Fixed
Routes connections through fixed WAN links.
Round-Robin
Evenly distribute the traffic over all WORKING WAN links in circular order according to the specified weights.
Considerring the example that distributing sessions over three WAN links withe the weight 3:1:2, Auto Routing will
distribute sessions to the WAN links in the order of WAN1, WAN1, WAN1, WAN2, WAN3, WAN3. In case of failure
happening on WAN2, Auto Routing distributes sessions in the order of WAN1, WAN1, WAN1, WAN3, WAN3.
By Connection
Compares the number of current connections on each WAN link and routes connections over WAN links based on a
specified ratio. The ratio for connections running among WAN links is the target that Auto Routing have to achieve and
keep by distributing connections appropriately. Considering the example that ratio of WAN1 to WAN2 to WAN3 is
1:1:2. At the begining, numbers of running connection on the WAN links are zero, so that the first three connections go
to WAN1, WAN2 and WAN3 respectively. Auto Routing has to distribute the forth connection to WAN3 to achieve the
ratio 1:1:2. Next, the fifth and sixth connection will be routed to WAN1 and WAN2 respectively, and the current ratio of
FortiWAN Handbook
Fortinet Technologies Inc.
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