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False FIB Entries of Slot of NE80 Contributes to Route Loop

Publication Date:  2012-07-27 Views:  70 Downloads:  0
Issue Description
Topology: PC-----S8016------NE80_1(221.6.161.1/30)-------(slot10 221.6.161.2/30)  NE80_2(221.6.161.110/30) -----------(221.6.161.109/30)network egress --------(202.38.64.9/19) website 
A PC cannot ping to the website of 202.38.64.9/19; perform tracert command to the address at PC and NE80_1, and a loop between NE80_1 and NE80_2 is found;  NE80_2 can perform the tracert command for the address normally. 
      
Alarm Information
Null
Handling Process
The problem is resulted from false FIB entries of LPU. To recover the services, update the routes. There are two methods as follows, which can be selected accordingly. 
1. Perform the reset command for routing protocols such as OSPF to boot re-learn of routes. This method is featured by that all entries will be updated, without any left. However, it will interrupt the services.  
2. At the problematic device, configure a static route with high priority of which the next hop is the NULL0 interface for the network; then, delete it at once. The strength lies in that the update is fast, without influence on other services, but the disadvantage is that only one route can be updated; if a lot of routes meet the problem, it is not suggested to use this method. 
    Both are common methods to troubleshoot the problem. Since the problem of established network is very complicated, it is suggested to confirm if the operation is feasible. 
Root Cause
Check the routing table and FIB of the MPU of NE80_1 and NE80_2, and both are normal; enter diagnosis mode, and check the FIB entries of slots on NE80_1 and NE80_2, and it is found that the FIB entries of slot 10 of NE80_2 are abnormal, of which the next hop is 221.6.161.109/30. The entries of other slots are normal, as follows:
[YZ-C-JFQ-NE80-2-diag]disp efu fib 10 202.38.64.9 19
[YZ-C-JFQ-NE80-2-diag]                                                          
 IP address              = 192.0.0.0                                            
 IP prefixLength         = 2                                                    
 VRF index               = 0                                                    
 Signature               = 0                                                    
 ecmpThr1                = 100                                                  
 ecmpThr2                = 0                                                    
          nextHop[0] ipaddr = 221.6.161.1                                       
          tegressContext = 0                                                    
          tb = 5 tp = 0x2 subIndex = 0                                          
          nextHop[0] actionFlags = 0x00000000 :    
                             
[YZ-C-JFQ-NE80-2-diag]disp efu fib 1 202.38.64.9 19                             
 Start display lpu fib on board 01...                                           
 Message sending success.                                                       
                                                                                
[YZ-C-JFQ-NE80-2-diag]                                                          
 IP address              = 202.38.64.0                                          
 IP prefixLength         = 19                                                   
 VRF index               = 0                                                    
 Signature               = 0                                                    
 ecmpThr1                = 100                                                  
 ecmpThr2                = 0                                                    
          nextHop[0] ipaddr = 221.6.161.109                                     
          tegressContext = 0                                                    
          tb = 11 tp = 0x0 subIndex = 0                                         
          nextHop[0] actionFlags = 0x00000000 :  
                               
Suggestions
Null

END