Figure
shows a network
setup in which the R1 serial link is unnumbered to loopback interface, while
the R2 serial link is numbered.
When OSPF creates a router LSA for
point-to-point links, it adheres to the following rule to fill the Link ID and
Link Data fields within the router LSA.
The Link
Data field for unnumbered point-to-point links should have a MIB-II Index
value. Because the link data value of the numbered interface does not match
that of the unnumbered interface, this creates a discrepancy in the OSPF
database.
Debugs and Verification
Figure
shows the
discrepancy in the OSPF database. The R1 router LSA shows the MIB-II index
value in the Link Data field for Serial 0, while the R2 router LSA shows the
router serial interface in the Link Data Field.
Figure
shows the
configuration on both R1 and R2, with the R1 serial interface unnumbered to a
loopback address, and the R2 serial interface numbered.
Solution
To fix this problem, both sides need to be either a
numbered point-to-point link or an unnumbered point-to-point link. Figure
shows the new
configuration that solves this problem.