Which four statements are correct regarding IS-IS operations? (Choose four.)
A . By default, Level 1 routers within an IS-IS area do not carry any routing information external to the area to which they belong. They use a default route to exit the area.
B . Summarization should be configured on the Level 2 routers, which injects the Level 2 routes into Level 1.
C . IS-IS supports "route leaking" in which selected Level 2 routes can be advertised by a Level 1/Level 2 router into Level 1.
D . The IS-IS backbone is a contiguous collection of Level 1 capable routers, each of which can be in a different area.
E . With IS-IS, an individual router is in only one area, and the border between areas is on the link that connects two routers that are in different areas.
F . Cisco IOS XR Software supports multitopology for IPv6 IS-IS unless single topology is explicitly configured in IPv6 address-family configuration mode.
Answer: A,C,E,F