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Not All Webpages Can Be Opened Due to the Defect of the NE40NE80 in Processing Default Routes of Short Masks

Publication Date:  2012-07-27 Views:  44 Downloads:  0
Issue Description
Networking topology: 
                            |       | 
                      NE80-1   NE80-2
                            |  \  / |  
                            |  /  \ |
                       5200     S8505

The users attached to the S8505 access public networks through NE80-2.
Two default routes are configured on NE80-2.
ip route-static 0.0.0.0 0.0.0.0 61.236.79.209
ip route-static 0.0.0.0 0.0.0.0 61.236.79.17
The upstream traffic is transmitted through the default routes.
Symptom of the fault:
The PCs attached to the S8505 can normally access the websites except www.baidu.com. 
 
Alarm Information
Null
Handling Process
1. View the routing table of NE80-2. The table is found normal.
2. Collect information about the default routes of the current network. The information shows that only the following two routes exist after the NPS split the two default routes into four:
IP=0.0.0.0, prefix=2, Th0=50, Th1=100, Color=0x0,qppb=0x0
[0] ip=61.236.79.17, hop_action=0x0, tb=0xB, tp=0x3, subindex=0 ,eContext=0
out_port_type = 3
[1] ip=61.236.79.209, hop_action=0x0, tb=0x9, tp=0x3, subindex=0 ,eContext=0
out_port_type = 3
[2] ip=0.0.0.0, hop_action=0x0, tb=0x0, tp=0x0, subindex=0 ,eContext=0
out_port_type = 0
IP=192.0.0.0, prefix=2, Th0=50, Th1=100, Color=0x0,qppb=0x0
[0] ip=61.236.79.17, hop_action=0x0, tb=0xB, tp=0x3, subindex=0 ,eContext=0
out_port_type = 3
[1] ip=61.236.79.209, hop_action=0x0, tb=0x9, tp=0x3, subindex=0 ,eContext=0
out_port_type = 3
[2] ip=0.0.0.0, hop_action=0x0, tb=0x0, tp=0x0, subindex=0 ,eContext=0
out_port_type = 0
The following two routes are lost:
IP=64.0.0.0, prefix=2, Th0=50, Th1=100, Color=0x0,qppb=0x0
[0] ip=61.236.79.17, hop_action=0x0, tb=0xB, tp=0x3, subindex=0 ,eContext=0
out_port_type = 3
[1] ip=61.236.79.209, hop_action=0x0, tb=0x9, tp=0x3, subindex=0 ,eContext=0
out_port_type = 3
[2] ip=0.0.0.0, hop_action=0x0, tb=0x0, tp=0x0, subindex=0 ,eContext=0
out_port_type = 0
IP=128.0.0.0, prefix=2, Th0=50, Th1=100, Color=0x0,qppb=0x0
[0] ip=61.236.79.17, hop_action=0x0, tb=0xB, tp=0x3, subindex=0 ,eContext=0
out_port_type = 3
[1] ip=61.236.79.209, hop_action=0x0, tb=0x9, tp=0x3, subindex=0 ,eContext=0
out_port_type = 3
[2] ip=0.0.0.0, hop_action=0x0, tb=0x0, tp=0x0, subindex=0 ,eContext=0
out_port_type = 0
Because the IP address of www.baidu.com is 119.75.213.50, the forwarding entry should match IP=64.0.0.0, prefix=2, Th0=50, Th1=100, Color=0x0, qppb=0x0. This route, however, is lost. Therefore, users cannot open Baidu webpages.
3. Workaround
Delete the following default routes:
Undo ip route-static 0.0.0.0 0.0.0.0 61.236.79.209
Undo ip route-static 0.0.0.0 0.0.0.0 61.236.79.17
Split the IP addresses as follows:
Split ip route-static 0.0.0.0 0.0.0.0 61.236.79.209 into four routes with the same mask:
ip route-static 0.0.0.0 192.0.0.0 61.236.79.209
ip route-static 64.0.0.0 192.0.0.0 61.236.79.209
ip route-static 128.0.0.0 192.0.0.0 61.236.79.209
ip route-static 192.0.0.0 192.0.0.0 61.236.79.209
Split ip route-static 0.0.0.0 0.0.0.0 61.236.79.17 into four routes with the same mask:
ip route-static 0.0.0.0 192.0.0.0 61.236.79.17
ip route-static 64.0.0.0 192.0.0.0 61.236.79.17
ip route-static 128.0.0.0 192.0.0.0 61.236.79.17
ip route-static 192.0.0.0 192.0.0.0 61.236.79.17
The problem is thus solved. 
 
Root Cause
Downlink users access www.baidu.com (119.75.213.50/51) through the following default routes:
ip route-static 0.0.0.0 0.0.0.0 61.236.79.209
ip route-static 0.0.0.0 0.0.0.0 61.236.79.17
The mask length of the default routes is 0. In the current NE40/80 version, the NPS splits the routes whose mask lengths are smaller than 2. For example, the NPS splits 0.0.0.0/0 as follows:
IP=192.0.0.0, prefix=2, Th0=100, Th1=0 Color=0x0
IP=128.0.0.0, prefix=2, Th0=100, Th1=0 Color=0x0
IP=64.0.0.0, prefix=2, Th0=100, Th1=0 Color=0x0
IP=0.0.0.0, prefix=2, Th0=100, Th1=0 Color=0x0
If there is another route 0.0.0.0/2, the IP address conflict occurs. In this case, the NPS deletes either of the two, 0.0.0.0/0, for example. Then the 0.0.0.0/2 route loses effect. If the 0.0.0.0/2 route is deleted, the 0.0.0.0/0 route cannot take effect completely.
On the existing network, the mask lengths of non-default routes are seldom smaller than 2. The problem in this case is caused by the IBM algorithm, which cannot be solved at present. Therefore, when the NE40/80 processes routes whose mask lengths are smaller than 2, the forwarding entries may be lost during the update of such routes. As a result, the services are affected. 
 
Suggestions
Owing to the hardware restriction, the chip of the LPU cannot process routes of short masks whose lengths are smaller than 2. During the update of short-mask routes, forwarding entries may be lost. In this case, because the route entries are normal on the SRU/MPU, you can run corresponding commands to re-update the routing table. In this manner, the forwarding entries on the LPU resume to normal. The current solution to this problem is to upgrade the version of the NE40/80 to V300R005 322, with the patch loaded. In versions later than V300R005 322, this problem is thoroughly solved.
Workaround for the problem on the current network:
1. If no dynamic routing protocol is used for advertising default routes, you can manually configure four default routes to avoid the preceding problem.
2. If the default routes can be dynamically learned on the current network, it is recommended that you upgrade the version of the router. 
 

END