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OSPF Default Routes Do Not Have Equal Cost Values Due to the Different Cost Values of Routes to Adv Router

Publication Date:  2012-07-27 Views:  2 Downloads:  0
Issue Description
Symptom of fault:
For the networking, see the appendix. The NE80E and 7609 are connected with two devices at an upper layer respectively. Enable OSPF. The NE5000E and GSR advertise the OSPF default routes. On the NE80E, the two default routes have no equal cost values. However, on 7609, it can be viewed that the default routes have equal cost values.
[NE80E]dis ip rou
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Tables: Public
Destinations : 1480 Routes : 1493

Destination/Mask         Proto    Pre   Cost      Flags NextHop       Interface

0.0.0.0/0                       O_ASE   150        1         D x.x.223.13        GigabitEthernet1/0/0
View LSDB, and you can find the LSA of the two default routes. Why are the cost values of the default routes different?
Type : External
Ls id : 0.0.0.0
Adv rtr : x.x.16.36
Ls age : 675
Len : 36
Options : DC
seq# : 80004efa
chksum : 0xb312
Net mask : 0.0.0.0
TOS 0 Metric: 1
E type : 2
Forwarding Address : 0.0.0.0
Tag : 1

Type : External
Ls id : 0.0.0.0
Adv rtr :x.x.16.31
Ls age : 869
Len : 36
Options : DC
seq# : 80004ed3
chksum : 0x20d1
Net mask : 0.0.0.0
TOS 0 Metric: 1
E type : 2
Forwarding Address : 0.0.0.0
Tag : 1 

 
Alarm Information
Null
Handling Process
Make the cost values of routes linking the NE80E with the NE5000E and GSR equivalent, and you can find on the NE80E that the cost values of the two default routes are equal. 
Root Cause
The NE80E of Huawei is manufactured in strict accordance with RFC 2328. When the cost values are equal, the equipment continues to compare the cost values of routes to the ASBRs and prefers the smallest.
View the cost values of the routes linking the NE80E with the two ASBRs.
<NE80E>dis ospf abr-asbr
OSPF Process 1 with Router ID x.x.88.147
Routing Table to ABR and ASBR
Intra-area       x.x.16.31      0.0.0.0      2     x.x.223.13      ASBR
Intra-area       x.x.16.36      0.0.0.0      3     x.x.223.13      ASBR
You can view that the cost value of one route is 2 and that of the other is 3. This indicates that no equal cost routes exist on the NE80E. Why are there two equal cost routes on 7609? After consultation, it is found that the C equipment is not manufactured in strict accordance with RFC 2328. If the cost values of E2 routes are equivalent, equal cost routes are created directly. 
 
Suggestions
Null

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