Symptom
1. OSPF does not install a route in RIB for type-5 LSA with forwarding address;
2. "show ip ospf rib " gives empty output;
# sh ip ospf 1001 rib 10.17.69.17
OSPF Router with ID (192.0.2.1) (Process ID 1001)
Base Topology (MTID 0)
OSPF local RIB
Codes: * - Best, > - Installed in global RIB
LSA: type/LSID/originator
3. "show ip route " is in RIB and internal from the correct OSPF process
3b. debugging the prefix one would see
OSPF-1001 EXTER: Start processing AS External LSA 5/10.0.33.0/192.0.2.222, mask 255.255.255.192
OSPF-1001 EXTER: age 241, seq 0x80000001, metric 20, metric-type 2, fw-addr 10.17.69.17
OSPF-1001 EXTER: Failed to find route to forwarding address
Conditions
1. LSA type-5 has a fwaddr
2. The fwaddr is covered by LSA type-3
3. the Type-3 LSA somehow flapped from longer to shorter match (was /24 and became /23 due to aggregation).
Workaround
Either "clear ip ospf rib" or restart the affected OSPF process.
