I assume you mean management traffic - device updates, licensing, etc. and not user traffic. By default all management traffic exits via the management interface. If you want it to exit another route, this can be configured via Service Route Configuration (Device -> Setup -> Services) If it is what you are intending to do, I recommend against having this traffic exit directy to an untrusted network. Instead, have it exit to an internal network, then traverse back through the firewall to be scanned, just in case something nefarious is going on.
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