Which command enables authentication at the OSPFv2 routing process level?
A. area 0 authentication message-digest
B. area 0 authentication ipsec spi 500 md5 1234567890ABCDEF1234567890ABCDEF
C. ip ospf authentication message-digest
D. ip ospf message-digest-key 1 md5 C1sc0!
Routing process Level
area 0 authentication message-digest
Interface Level
ip ospf authentication message-digest
A