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Troubleshooting Guide

CloudEngine 16800, 12800, 12800E, 8800, 7800, 6800, and 5800 Series Switches

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BGP Summary Route Flaps

BGP Summary Route Flaps


BGP, Summary Route, Route Flaps


The BGP routes learned by SW1 and SW2 from R1 flap.

Problem Description

Figure 14-16 Networking diagram

Fault Symptom

The BGP routes learned by SW1 and SW2 from R1 flap.


  1. Static routes are first imported to OSPF process 500 based on routing policies.
  2. After importing a static route, OSPF process 500 calculates an O_ASE route accordingly and advertises it through an LSA to SW2.
  3. OSPF process 1 imports the O_ASE route from OSPF process 500 through SW2, calculates an O_ASE route accordingly, and then advertises the calculated O_ASE route through an LSA to SW1.
  4. An O_ASE route has a higher priority than a static route. SW1 then replaces the static route with the O_ASE route in the routing table and notifies the event to SW2. After SW2 learns that the static route is replaced, SW2 notifies that the O_ASE route in OSPF process 500 becomes ineffective. As a result, the O_ASE route in OSPF process 1 also becomes ineffective.
  5. OSPF process 1 withdraws the O_ASE route and notifies the event to SW1. Then the static route in the routing table on SW1 becomes active.
  6. OSPF process 500 imports the static route again, and the preceding process repeats itself. As a result, the preferred route frequently alternates between OSPF and static routes in routing tables of SW1 and SW2.
  7. SW1 and SW2 import BGP routes using the network command. If the preferred route alternates between OSPF and static routes in routing tables of SW1 and SW2, BGP routes will be withdrawn and then learned again. Consequently, the IGP route on R1 will also flap.


Run the ip route-static ip-address { mask | mask-length } { nexthop-address | vpn-instance vpn-instance-name nexthop-address } [ preference preference | tag tag ] command on SW1 and SW2 to adjust the preference of the static route from 200 to 60 so that the static route remains preferred in routing tables of SW1 and SW2.

Updated: 2020-01-07

Document ID: EDOC1000060766

Views: 615063

Downloads: 2962

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