I am using the following network in GNS3

The topology is probably irrelevant here but I am trying to create a AAA Authentication list for logging in on IOS-XR7. However I cannot specify that the router check the TACACS+ server before the local database:
RP/0/0/CPU0:IOS-XR7(config)#aaa authentication login LIST_NAME ?
local Use local username authentication
RP/0/0/CPU0:IOS-XR7(config)#
It is not until I enter local that I can then go on to configure the group tacacs+ command. My TACACS+ server is already configured and committed:
tacacs-server host 10.1.1.100 port 49
key 7 13164411195F10
There is no actual TACACS+ server on the network but it should still work right? Or am I missing something fundamental...?