Fault Analysis
1. Run the undo ip route-static 0.0.0.0 0.0.0.0 192.168.0.65 command on Router A, and then
view the details about the corresponding LSA on Router C. The FA field of the LSA is
incorrectly set by Router A. In this case, Router C has an OSPF default route to only
Router B, because Router C finds that the route to address 192.168.0.69 is unreachable
when performing SPF calculation.
2. Run the undo ip route-static 0.0.0.0 0.0.0.0 192.168.0.1 command on Router B, and then
view the details about the corresponding LSA on Router C. The FA field of the LSA is
incorrectly set by Router B. In this case, Router C has an OSPF default route to only
Router A, because Router C finds that the route to address 192.168.0.5 is unreachable when
performing SPF calculation.
3. The preceding analysis shows that the root cause of the fault is that Router A and Router
B incorrectly set the FA fields in the corresponding LSAs.
The rules the router uses to fill in the FA fields of LSAs and calculate routes are as follows:
l When the value of the FA field of a Type 5 LSA is 0.0.0.0, the router that receives the
LSA knows that the router sending the LSA is an advertising router (that is, an ASBR),
and calculates the next hop.
l When all of the following conditions are met, an ASBR fills in an address other than
0.0.0.0 in the FA field of a Type 5 LSA, and the router that receives the LSA calculates
the next hop based on the value of the FA field:
a. OSPF is enabled on the interface connecting the ASBR to an external network.
b. The interface connecting the ASBR to an external network is not configured as a
silent interface.
c. The network type of the interface connecting the ASBR to an external network is
not P2P or P2MP.
d. The address of the interface connecting the ASBR to an external network is within
the network address range advertised by OSPF.
If none of the preceding conditions are met, the FA field of an LSA is set to 0.0.0.0.
Procedure
Step 1 Do as follows to rectify the fault:
l Check the data configuration on Router A and Router B, the following information can be
found:
– The network 192.168.0.68 0.0.0.3 command rather than the network 192.168.0.64
0.0.0.3 command is run in the OSPF process on Router A.
– The network 192.168.0.4 0.0.0.3 command rather than the network 192.168.0.0
0.0.0.3 command is run in the OSPF process on Router B.
l In the OSPF process on Router A, delete the network command used to advertise the network
segment to which the next hop of the configured static route corresponds. Perform the same
operation on Router B. Then, the fault is rectified.
l Run the ospf network-type p2p command on the interface specified in the network
command run on the Router A to change the network type of the interface. Then, perform
the same operation on Router B. After that, the fault is rectified.
Huawei AR2200-S Series Enterprise Routers
Troubleshooting 7 IP Forwarding and Routing
Issue 01 (2012-01-06) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
199
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