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Users Failed to Access the Internet Because the UNR Was Imported only to the IS-IS Level 2 Network by Default

Publication Date:  2013-09-30 Views:  108 Downloads:  0

Issue Description

Networking: Internet--Router--ME60--Dslam--Modem—Clients

Version: ME60 V100R005 and later

Symptom: An ME60 communicated with the uplink router using IS-IS. The ME60 was configured with IS-IS level 1-2. Users went online properly but failed to access the Internet. In addition, pinging the external network failed. On ME60, import unr had been configured under the IS-IS view.

Handling Process

Huawei performed the following operations to address the problem:

1. Analyzed the symptom and suspected that the problem was caused by a route-related fault.

Users going online properly indicated that the ME60 communicated with the AAA servers properly.

2. Performed tracert tests after a user went online.

The test succeeded only between the client and the ME60.

3. Checked the routing table on the ME60.

The routing table contained a UNR.

display ip routing-table 2x.x.186.100                
Route Flags: R - relay, D - download to fib                                     
Routing Table : Public                                                          
Summary Count : 1                                                               
Destination/Mask    Proto  Pre  Cost     Flags NextHop         Interface        
   2x.x.186.100/32  Unr    61   0           D  2x.x.186.100     InGigabitEthenet1/0/0.1

However, the routing table on the uplink router did not contain a corresponding UNR although import unr had been configured.

isis 1                                                                          
 network-entity 00.0005.0000.0000.0002.00                                       
 import-route unr                                                               

4. Checked the ISIS LSDB on the ME60 and found that the UNR existed only in the IS-IS level 2 network.

Information for ISIS(1)                        
                          Level-1 Link State Database                           
LSPID                 Seq Num      Checksum      Holdtime      Length  ATT/P/OL 
0000.0000.0002.00-00* 0x00000002   0x4921        481           35      0/0/0    
 SOURCE       0000.0000.0002.00                                                 
 AREA ADDR    00.0005                                                           
    *(In TLV)-Leaking Route, *(By LSPID)-Self LSP, +-Self LSP(Extended),        
           ATT-Attached, P-Partition, OL-Overload                               
        //Level 1 IS-IS did not import the UNR                                                                       
                          Level-2 Link State Database                           
LSPID                 Seq Num      Checksum      Holdtime      Length  ATT/P/OL 
0000.0000.0002.00-00* 0x00000003   0x4722        480           35      0/0/0    
 SOURCE       0000.0000.0002.00                                                 
 AREA ADDR    00.0005                                                           
0000.0000.0002.00-01* 0x00000003   0x99bf        477           463     0/0/0    
 SOURCE       0000.0000.0002.00                                                 
 IP-External  59.x.x.0    COST: 64                          
 IP-External  2x.x.186.0    COST: 64      
//Level 2 imported the UNR                    
 IP-External  59.x.x.64  COST: 64                   

Because the ME60 ran ISIS level 1-2 by default and the uplink router ran IS-IS level 1, the UNR was not advertised to the uplink router.

5. Configured import unr level-1 on ME60.

The uplink router properly learned the UNR and users accessed Internet successfully.

isis 1                                                                          
 network-entity 00.0005.0000.0000.0002.00                                       
 import-route unr level-1

Root Cause

By default, import unr on ME60 imported the UNR to the IS-IS level 2 network, but IS-IS level 1 ran between the ME60 and the uplink router. Therefore, the UNR was not advertised to the uplink router, causing Internet access failure. Other routes, including interface routes, direct routes, and static routes could be imported to the level 1 network. Therefore, users could go online.


Configured import unr level-1 on ME60.


By default, import unr level-1-2 is configured on ME60 and IS-IS level 2 is configured on the uplink backbone area for an ME60. If the UNR does not need to be advertised in level 2 network, services are normal under these default configurations. Otherwise, configure import unr level-1 on ME60. MA5200G VRP5.30 has the same problem.