Switching between last two buffers in vim

• Ctrl-6
• Ctrl-^

:ls

a  - active buffer (the one we see in the window)
h  - hidden buffer (not in the window and has unsaved changes )
#  - alternate buffer
+  - buffer modified (unsaved)

To switch back-and-forth two buffers:

Ctrl-^ (Ctrl-Shift-6)
Ctrl-6