OSPF routes flapping between the ip address of the 2 chassis in DBHA

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Article ID: 167945

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Updated On:

Products

XOS

Issue/Introduction

Identical OSPF Router IDs on 2 vap-groups on the chassis would cause route flapping on the adjacent router. If two or more vap-groups in the chassis are configured to run OSPF then unique OSPF router ID should be manually configured for each OSPF configuration on the chassis.The routes on the router connected to the flap between the ip addresses configured between the 2 chassis and the default route:
In the followig example, subnet 10.47.197.64/27 is directly connected to the 2 chassis's with circuit ip addresses for the vap-group configured as 10.47.196.101 and 10.47.196.102, and the default route on the router set to 10.47.192.13.


txsat1swidcc01-Internet_Edge# sho ip rout 10.47.197.64
IP Route Table for VRF "default"
'*' denotes best ucast next-hop
'**' denotes best mcast next-hop
'[x/y]' denotes [preference/metric]
'%<string>' in via output denotes VRF <string>

10.47.197.64/27, ubest/mbest: 1/0
*via 10.47.196.101, Vlan504, [110/100], 00:00:04, ospf-54775, intra

txsat1swidcc01-Internet_Edge# sho ip rout 10.47.197.64
IP Route Table for VRF "default"
'*' denotes best ucast next-hop
'**' denotes best mcast next-hop
'[x/y]' denotes [preference/metric]
'%<string>' in via output denotes VRF <string>

10.47.197.64/27, ubest/mbest: 1/0
*via 10.47.196.102, Vlan504, [110/50], 00:00:02, ospf-54775, intra

txsat1swidcc01-Internet_Edge# sho ip rout 10.47.197.64
IP Route Table for VRF "default"
'*' denotes best ucast next-hop
'**' denotes best mcast next-hop
'[x/y]' denotes [preference/metric]
'%<string>' in via output denotes VRF <string>

0.0.0.0/0, ubest/mbest: 1/0
*via 10.47.192.13, Po11, [110/1], 00:19:30, ospf-54775, type-2, tag 54775


Cause

Problem: If the 2 vap-groups configured on the chassis are running OSPF, and if the router ID for the 2 vap-groups are identical then the adjacent router may experience route flapping for the routes on the 2 vap-groups.
As the router has neighbor adjacencies established with both vap-groups, it receives updates from both of them for the same router ID, which causes the flapping.

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In the above example, the following is seen on the router:
'Show ip ospf neighbor' shows that the router ID for the 2 vap-groups are identical i.e. vlan504 and vlan503 which belong to 2 different vap-groups have the same router ID 198.74.88.8 on chassis A, where the neighbor addresses are 10.47.196.101 and 10.47.196.69. Similarly they have the same router ID 198.74.88.9 on chassis B

Cisco_router#sho ip ospf nei

OSPF Process ID 54775 VRF default
Total number of neighbors: 11
Neighbor ID Pri State Up Time Address Interface
10.47.197.252 1 FULL/DR 2d22h 10.47.196.99 Vlan504
198.74.88.8 0 FULL/DROTHER 2d22h 10.47.196.101 Vlan504
198.74.88.9 0 FULL/DROTHER 2d22h 10.47.196.102 Vlan504
10.47.197.252 1 FULL/BDR 1w2d 10.47.196.67 Vlan503
198.74.88.8 0 FULL/DROTHER 3d23h 10.47.196.69 Vlan503
198.74.88.9 0 FULL/DROTHER 3d23h 10.47.196.70 Vlan503


########
circuit configuration on Chassis A:

circuit vlan503 circuit-id 1028 domain 503
device-name vlan503
vap-group INETFW
default-egress-vlan-tag 503
ip 10.47.196.69/27 10.47.196.95


circuit vlan504 circuit-id 1025 domain 504
device-name vlan504
vap-group DMZFW
default-egress-vlan-tag 504
ip 10.47.196.101/27 10.47.196.127

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Resolution

If there are 2 or more vap-groups configured on the chassis and are running OSPF, then unique router IDs should be manually configured for each OSFP configuration.

Here is an example:
------------

OSPF configuration of vap-group INETFW on chassis A:
router ospf 54775
 ospf router-id 198.74.88.8

-------
OSPF configuration of vap-group DMZFW on chassis A:
router ospf 54775
 ospf router-id 10.10.10.101

--------

OSPF configuration of vap-group INETFW on chassis B:
router ospf 54775
ospf router-id 198.74.88.9

-------
OSPF configuration of vap-group DMZFW on chassis B:
router ospf 54775
ospf router-id 10.10.10.102

Workaround

N/A