Configure SD-WAN rules to govern the steering of DSCP tag-based traffic to the appropriate interfaces. Traffic will be steered based on the Criteria configured as part of the SD-WAN rules configuration.
In our example, we configured three different SD-WAN rules to govern DSCP tagged traffic. We have one SD-WAN rule each for VoIP traffic, social media traffic (Facebook in this case), and all other web traffic. VoIP traffic is always steered to either of the two overlay SD-WAN zones -
VPN_B_tunnel(Branch-HQ-B). Similarly, social media traffic and other web traffic is always steered to either of the two underlay SD-WAN zones -
Internet_B(port5). The interface that is preferred by the system over another depends upon the Criteria configured in the SD-WAN rule definition.
We configured the following SD-WAN rules:
config sys sdwan config service edit 5 set name "VoIP-Steer" set mode priority set tos 0x70 set tos-mask 0xf0 set dst "all" set health-check "Default_DNS" set link-cost-factor jitter set priority-members 4 3 next end end
VoIP-Steer SD-WAN rule configured above governs the DSCP tagged VoIP traffic.
DSCP values commonly are 6-bit binary numbers that are padded with zeros at the end. Therefore, in this example, VoIP traffic with DSCP tag
011100 will become
01110000. This 8-bit binary number
01110000 is represented in its hexadecimal form
0x70 as the
tos (Type of Service bit pattern) value. The
tos-mask (Type of Service evaluated bits) hexadecimal value of
11110000) is used to check the four most significant bits from the
tos value in this case. Hence, the first four bits of the
0111) will be used to match the first four bits of the DSCP tag in our policy above. Only the non-zero bit positions are used for comparison and the zero bit positions are ignored from the
We used the Best Quality strategy to define the Criteria to select the preferred interface from the overlay SD-WAN zone. With the Best Quality strategy selected, the interface with the best measured performance is selected. The system prefers the interface with the least Jitter.
For more information about configuring SD-WAN rules with the Best Quality strategy, see Best quality strategy.
FortiGate # config sys sdwan