Content

| 5.7 |  | Troubleshooting OSPF |
| 5.7.3 |  | One side of point-to-point link is unnumbered |

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 IfIndex 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.