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The NE80 and the Competitor's Device, Both Serving as the ABRs of an NSSA, Cannot Implement Switchover Due to Different RFC Implementation Mechanisms

Publication Date:  2012-07-27 Views:  49 Downloads:  0
Issue Description
Version: NE40/80 V300R005C01B322
Topology: See the appendix.
Symptom of the fault: When the uplink port of the NE80 on a MAN is Down, it is found that the default route of the NE80 on the MAN and that of the device attached to the competitor’s 7304 both point to the competitor’s 7304. However, from the NE80E and the NE80 on the provincial backbone network, it is still found that Type 5 LSAs (converted by the ABR) within the MAN are advertised by only the NE80. In addition, no information about the conversion of Type 7 LSAs advertised by the 7304 to Type 5 LSAs can be found. Meanwhile, the services are interrupted. 
 
Alarm Information
Null
Handling Process
1. View configuration information. The result shows that the configuration is correct.
2. According to OSPF, only the ABR is capable of implementing Type 7 to Type 5 LSA conversion. When more than one ABR exists in an NSSA, according to previous RFC specifications, only the ABR with a greater router ID can implement such conversion. The latest specification, RFC 3101, specifies that we can designate one of the ABRs in the NSSA for the Type 7 to Type 5 LSA conversion.
3. Check the device: The OSPF neighbor of the NE80 in the backbone area still implements LSA conversion. According to the lab analysis and on-site test, the competitor’s 7304 implements the conversion according to RFC 1583 instead of the latest RFC 3101. As a result, when the NE80 is shut down upstream, the 7304 fails, in the backbone area, to detect the unreachability of the NE80 and so still deems it as the ABR. Therefore, the 7304 does not convert Type 7 LSAs to Type 5 LSAs. This explains why services are interrupted.
4. Ask the customer to upgrade the competitor’s router to the master one, that is, change the router ID to a greater value. After the change, the fault is rectified. 
 
Root Cause
1. The configuration of the NE80 is incorrect.
2. Type 7 LSAs cannot be properly converted to Type 5 LSAs.
3. Other problems. 
 
Suggestions
When the routers from different vendors serve as the ABRs in an NSSA, it is recommended that you first conduct the switchover test and plan the networking properly to avoid the network breakdown caused by different implementation mechanisms. 

END