+ A NAT gateway selects ports at random from the available pool of ports. If there aren't available ports, SNAT ports are reused as long as there's no existing connection to the same destination public IP and port. In order for a SNAT port to be reused to connect to the same destination endpoint, NAT gateway places a [SNAT port reuse cool down timer](/azure/nat-gateway/nat-gateway-resource#port-reuse-timers) on the port after the preceding connection closes. The SNAT port reuse timer helps prevent ports from being selected too quickly for connecting to the same destination repeatedly. This reuse cool down timer is helpful in scenarios where destination endpoints have firewalls or other services configured that place a cool down timer on source ports. This port selection and reuse behavior of a NAT gateway makes it less likely to experience connection timeouts.
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