Technical Tip: Using Zoom with IPv4 DoS Policy

wmichael · ‎02-08-2024

Description

This article describes how to configure an IPv4 Dos Policy on FortiGate for use with Zoom meetings.

Zoom meetings generate a large amount of UDP packets. Due to the large volume of UDP packets the, udp_flood on an IPv4 Dos policy can easily be triggered. This can cause a number of issues resulting in poor quality communication.

Scope

FortiGate.

Solution

Zoom requires TCP ports 80,443 and UDP ports 3478, 3479, 8801 - 8810.

See the Zoom network firewall or proxy server settings:
Zoom network firewall or proxy server settings

If the IPv4 DoS policy is causing Zoom UDP packets to drop by triggering the udp_flood, it is necessary to allow the UDP ports that Zoom uses.

This can be done in a separate IPv4 DoS policy so that the normal DoS policy is still effective.

Create a new service object that covers UDP ports 3478-3479 and 8801-8810. On the GUI, go to Policy & Objects -> Services and select 'Create New'.
Create the service object and have UDP destination ports 49152-65535 (ephemeral ports) and the source ports 3478, 3479, 8801 - 8810.

Here is an example of how the service object should be configured:

CLI configuration of the service:

config firewall service custom
    edit "Zoom UDP Ports"
        set udp-portrange 49152-65535:8801-8810 49152-65535:3478-3479
    next
end

Create a new IPv4 DoS policy. This IPv4 DoS policy will allow the UDP flood on the wan interface for Zoom by allowing packets on UDP ports 3478-3479, and 8801-8810. This IPv4 DoS policy is configured using the WAN interface where the UDP packets will come to the FortiGate from the Zoom server.
If another more general IPv4 DoS policy is already configured, it can be copied and the new policy can be pasted above the current one. The new policy can then be edited.

In this example, port1 was used. The interface needs to be the Internet-facing WAN interface.

Ensure udp_flood on the IPv4 DoS policy is set to either 'Disable' or 'Monitor'.

Ensure the new policy is above any general use IPv4 DoS policies. IPv4 DoS policies are matched from top to bottom, just like firewall policies.

CLI configuration of the IPv4DoS policy and udp_flood anomaly:

config firewall DoS-policy

edit 2

set name "Zoom-bypass"

set interface "port1"

set srcaddr "all"

set dstaddr "all"

set service "Zoom UDP Ports"

config anomaly

edit "udp_flood"

set status enable

set log enable

set action pass

set threshold 2000

To move the IPv4 DoS policy on the CLI use the following command:

move 2 before 1

The result will be that traffic from Zoom servers will hit the Zoom-bypass DoS policy and not trigger the udp_flood.

If the action is set to 'monitor' the traffic will pass through but will be shown in the Anomaly logs as 'detected'.