EXFO FTB-8500 Series for FTB-500 - Manual (Page 387)

System Tabs
Ethernet and Fibre Channel Application 373
IPv6 Test Preferences

Default Gateway Address: The Default Gateway Address is used to
forward packets outside the subnet. Default Gateway Address is not
available when the Global IPv6 address Mode is set to None.
Mode

Automatic allows automatic selection of the default gateway.

Static allows entering the default gateway IP address. The default
address is FE80::.