Which three statements about IS-IS are true? (Choose three.)
A. IS-IS can be used only in the service provider network.
B. IS-IS can be used to route both IP and CLNP.
C. IS-IS has three different levels of authentication: interface level, process level, and domain level.
D. IS-IS is an IETF standard.
E. IS-IS has the capability to provide address summarization between areas.
D is definitely correct. IETF originally documented IS-IS in RFC 1142, but later updated it with RFC 7142. It was developed by DEC, and first standardized by ISO, but it is also a ratified IETF standard per the RFCs listed.
C is not correct. There are three levels of authentication for IS-IS, but they are link-level, area-level, and domain-level. Link-level auth is of course configured on the interface connecting to other IS-IS routers you want to authentication with. Both area-level and domain-level authentication are configured on the “router isis” process and could (incorrectly) be called process-level authentication, but since that would not distinguish between the two, it is incorrect.
Correct Answer: BDE