No relevant resource is found in the selected language.

This site uses cookies. By continuing to browse the site you are agreeing to our use of cookies. Read our privacy policy>

Reminder

To have a better experience, please upgrade your IE browser.

upgrade

BGP Neighbors Become Down in the NE5000E Because of Route Iteration

Publication Date:  2012-07-27 Views:  16 Downloads:  0
Issue Description
Network topology:
                 10G POS(5/0/0)
NE5000E--------------------------Device of Company C
                 10GE(1/0/0)   
The NE5000E is connected to the device of Company C through double links. The NE5000E and the device of Company C establish BGP neighbor relationship through Loopback interfaces.
The IP address of the Loopback interface on the device of Company C is 10.0.0.1. The IP address of 10G POS interface on the device of Company C is 192.168.0.1/30.The IP address of 10GE interface on the device of Company C is 192.168.1.1/30.Fault description:
After the interface POS 5/0/0 of the NE5000E becomes Down, the BGP neighbor becomes Down and the status is opensend. However, the NE5000E can ping the Loopback interface of the device of Company C.
        
Alarm Information

The log buffer of the NE5000E reports BGP peer down.

Handling Process
Analyze first why an NULL0 interface appears and then analyze why NULL0 causes the BGP neighbors to become Down.
1. Why does one of the equal-cost routes change? The cause is that route iteration occurs. If no route iteration occurs, the previous two equal-cost routes are used for sending upstream packet, and only one of the equal-cost routes to 10GE 1/0/0 is left.
2. Check the configurations on the device and why the routes are iterated to NULL0.
On the NE5000E, configure static routes as follows destined for the Loopback interface of the device of Company C:
ip route-static 10.0.0.1 255.255.255.255 192.168.1.1
ip route-static 10.0.0.1 255.255.255.255 192.168.0.1
After the POS 5/0/0 of the NE5000E is Down, the preceding static routes cause the NE5000E to perform route iteration and search the routing table to check whether a route to remote 10G POS interface exists. The checking result shows that a route as follows exists:
ip route-static 192.168.0.0 255.255.255.0 NULL0 preference 255
It shows that the next hop of one of the equal-cost routes becomes NULL0 after the POS interface is Down.

3. Analyze the relationship between the NULL0 interface and the Down status of BGP neighbors. After the POS 5/0/0 is Down, the double upstream routes in the NE5000E are as follows:
Destination/Mask    Proto  Pre  Cost       NextHop         Interface
        0.0.0.0/0   BGP    100  0          10.0.0.1   GigabitEthernet1/0/0
                           BGP    100  0          10.0.0.1   NUll
0
I
n this situation, the NE5000E should be able to ping the IP address of the loopback interface on the device of the Company C. Usually, BGP neighbors should not be Down.

However, a problem occurs in the Hash algorithm for sending packets since the NE5000E has double upstream links. That is, the NE5000E sends ping packets without the source IP address through the 10GE interface, which is successful, but sends packets with the source IP address through the 10G POS interface, which fails. Because the NE5000E uses the POS interface to establish BGP neighbors with the device of Company C and the 10GE POS interface is iterated to the route of which the next hop is the NULL0 interface, BGP neighbor in the NE5000E becomes Down.
4. Solution:
The problem can be solved if only the route iteration can be ended. We add the next hop and outbound interface following the static route to end the route iteration.
ip route-static 10.0.0.1 255.255.255.255 192.168.1.1 ge 1/0/0
ip route-static 10.0.0.1 255.255.255.255 192.168.0.1 pos 5/0/0
According to the preceding configuration, the route iteration is ended after the POS 5/0/0 is Down. The NE5000E announces that the static route to the POS interface is unreachable and then removes that route form its routing table. After that, it sends all packets to the device of Company C through the GE interface. 


         
Root Cause

It is found out that after the interface POS 5/0/0 becomes Down, the next hop of one of the equal-cost routes is interface NULL0.
After POS 5/0/0 of the NE5000E is Down, the routes to the public network and the status of the corresponding BGP neighbors are as follows:
Before the interface POS 5/0/0 is Down, the routes to the public network are as follows:
[M-NN-LANGDONG-R-NE5000E-01]DISP IP ROU 219.133.0.3
Routing Table : Public
Summary Count : 2
Destination/Mask    Proto  Pre  Cost       NextHop         Interface
        0.0.0.0/0   BGP    100  0          10.0.0.1   GigabitEthernet1/0/0
                           BGP    100  0          10.0.0.1   Pos5/0/0

Suggestions

In VRPv5.3, the route iteration is implemented as the preceding mechanism and is enable by default. In networking, we must analyze whether route iteration can cause results that are not expected.

      

END