Users should be aware of the following potential issues when using default routing metrics:
Don’t set a default gateway for an interface unless you really want packets to be sent to that default gateway. It’s not necessary to always set one for an interface and doing so can cause problems.
If you configure multiple network interfaces, particularly VLANs, then the interface metrics (and therefore which default gateway traffic is actually sent to) will be assigned in the order they are configured. After a reboot the metrics may be assigned in a different order which may effect where packets are sent. The behaviour should be stable after subsequent reboots if the configuration stays the same. If in doubt, assign the metrics by hand.