Nokia Voyager Reference Manual page 187

Platform C are configured with IP addresses (10.10.10.2 and 101.10.10.1
respectively).
The interfaces that comprise the virtual link between Nokia Platform A and
Nokia Platform C are both configured as unnumbered. This link will fail
because OSPF does not support a virtual link that uses an unnumbered
interface on either end of the link. See RFC 2328 for more information. Any
virtual link that uses OSPF must have an IP address configured on both ends.
Voyager Reference Guide
Platform C
Backbone
Host PC
Virtual Link
Nokia
Unnumbered
Serial Link
10.10.10.1
Virtual Link
10.10.10.2
Host PC
Area 1
Host PC
Nokia
Platform A
Area 3
Nokia
Platform B
Host PC
Area 2
00044
187