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Route Convergence Is Slow Due to Inappropriate OSPF Area Planning on an NE40E

Publication Date:  2019-04-19 Views:  49 Downloads:  0
Issue Description

On the customer network, NetEngine40E-X C and & NetEngine40E-X D are interconnected with branches in different counties and districts. After the NetEngine40E-X3 is upgraded and restarted, OSPF route convergence is slow. OSPF route convergence on the entire network takes 48 minutes. The red box shown in the following figure indicates the involved area.

Handling Process

Check the device status.

Check the OSPF running status on NetEngine40E-X3 C and NetEngine40E-X3 D.

 

>display ospf error

No errors are displayed.

>display ospf lsdb | count

Total lines: 3727.

>display ospf peer brief

         OSPF Process 1 with Router ID 10.252.58.5

                  Peer Statistic Information

 ----------------------------------------------------------------------------

 Area Id          Interface                        Neighbor id      State   

 ----------------------------------------------------------------------------

 Total Peer(s):     0

 

         OSPF Process 200 with Router ID 10.252.58.5

                  Peer Statistic Information

 ----------------------------------------------------------------------------

 Area Id          Interface                        Neighbor id      State   

 0.0.0.0          GigabitEthernet1/0/7.3030        A.B.C.D          Full       

 ......

 0.0.y.z          GigabitEthernet3/0/7.7           E.F.G.H          Full       

 ----------------------------------------------------------------------------

 Total Peer(s):   279

 

>display ip routing-table

Route Flags: R - relay, D - download to fib

------------------------------------------------------------------------------

Routing Tables: Public

         Destinations : 2737     Routes : 4987    

 

>display ip routing-table protocol ospf

Route Flags: R - relay, D - download to fib

------------------------------------------------------------------------------

Public routing table : OSPF

         Destinations : 3727       Routes : 3727      

 

OSPF routing table status : <Active>

         Destinations : 3727       Routes : 3727

 

>display cpu-usage

CPU Usage Stat. Cycle: 60 (Second)

CPU Usage            : 87% Max: 93%

......

CPU utilization for five seconds: 86%: one minute: 88%: five minutes: 90%.

 

>display memory-usage

......

 Memory Using Percentage Is: 72%

 

Check the OSPF area planning. All non-backbone areas are common areas, and all the areas advertise network-wide routes.

Root Cause

The NetEngine40 needs to advertise network-wide routes to all routers on the network. Because there are many routes in the LSDB and the performance of downstream devices is limited, OSPF route convergence is slow.

Solution




Based on the negotiation with the customer, re-plan the non-backbone areas of OSPF. With a combination of the original network planning and the actual service conditions, migrate services from the non-backbone areas to newly built stub area or NSSA. This reduces the number of routes to be advertised during OSPF convergence on the NetEngine40E-X3 and quickens OSPF route convergence on the entire network.

 

Reference configuration:

1. Create an NSSA on the NE40.

>system-view

]ospf 200

]area 0.0.0.Y

]nssa

]default-route-advertise

]network (network segment address of the interface connecting to the newly built area)

 

2. Move the downlink router to the newly built area.

>system-view

]ospf 200

]area 0.0.0.X

]undo network X.W.Y.Z

]......

]quit

]undo area 0.0.0.X

]area 0.0.0.Y

]nssa

]network X.W.Y.Z(route to be advertised to the area)




Suggestions

During OSPF deployment, properly partition areas to reduce the LSDB scale and network traffic in order to ensure network performance.

END