Which three fields are optional in an OSPFv3 external LSA? (Choose three.)

A.
Forwarding Address

B.
External Route

C.
Link-State ID

D.
Option

E.
Prefix Options

Explanation:
AS-External LSA
As with OSPFv2, the AS-External LSA advertises prefixes external to the OSPF routing domain;
one LSA is required for each external prefix advertised. However, the format of the OSPFv3 AsExternal LSA (Figure 9-10) is different from its OSPFv2 counterpart.
Figure 9-10. OSPFv3 AS-External LSA

http://fengnet.com/book/CCIE%20Professional%20Development%20Routing%20TCPIP%20Volu
me%20I/images/09fig10_alt.jpg