OSPF neighbor uptime mismatch in cisco 1941

[netops044]

Hello,

Need solution for OSPF uptime mismacth issue.Observed ospf uptime mismatch between provider edge(PE) and customer edge(CE) router.

CE router  OSPF frequently flapping but PE router uptime is stable.

Router details:

Provider edge router:7206VXR (IOS:c7200-adventerprisek9-mz.124-15.T8.bin)

WAN int:

ip vrf forwarding TEST-VRF
 ip address XX.XX.XX.XX 255.255.255.252
 ip mtu 1500
 rate-limit input access-group 155 6144000 1152000 2304000 conform-action transmit exceed-action drop
 rate-limit output access-group 155 6144000 1152000 2304000 conform-action transmit exceed-action drop
 ip ospf network non-broadcast
 no cdp enable

OSPF:

router ospf 106 vrf TEST-VRF
 log-adjacency-changes
 redistribute connected subnets
 redistribute bgp 9583 subnets
 network XX.XX.XX.XX 0.0.0.3 area 0
 default-information originate
 address-family ipv4 vrf TEST-VRF
  redistribute connected
  redistribute static
  redistribute ospf 106 vrf TEST-VRF match internal external 1 external 2
  no synchronization

output:

PE#sh ip osp nei GigabitEthernet0/3.990246 det | i up

Neighbor is up for 4d00h

Customer edge router:CISCO1941/K9 (IOS:c1900-universalk9-mz.SPA.150-1.M4.bin)

Wan int :

 encapsulation dot1Q 246
 ip address XX.XX.XX.XX 255.255.255.252
 ip ospf network non-broadcast

OSPF:

router ospf 100
 log-adjacency-changes
 redistribute connected subnets
 redistribute static subnets
 network XX.XX.XX.XX  0.0.0.3 area 0
 neighbor XX.XX.XX.XX 

output:

CE#sh ip ospf neighbor GigabitEthernet0/0.246 detail | i up

Neighbor is up for 23:22:23

[Nagendra Kumar Nainar]

Hi,

Per my understanding, it depends on the neighbor state change. In normal P2P or broadcast network cases, when the link comes up after a flap, it immediately sends out OSPF hello. So the neighbor (that is up) will receive hello without its Router ID and so state goes from FULL to INIT or 1-way.

In your case, the network type is non-broadcast. So when the link comes up it will wait for some time before sending the hello. (Dont remember the timers though). In this interval, if PE sends the hello to CE with CE router id, CE will move directly to 2-way and the first hello sent from CE to PE will have PE router ID.

So on PE, the state change will be from FULL to EXSTART.

I hope in your setup you are seeing the below:

1. CE link flap doesnt not bring PE Link down.

2. CE link flaps and comes up within the PE OSPF dead interval time expires.

Can you please check if the above is true for your case?.

-Nagendra

[netops044]

Hi Nagendra,

Thanks for update.

Above said scenario exactly matching my case.

Please confirm ,If i can able change the network type to P2P/Broadcast up time will not mismatch??

[Nagendra Kumar Nainar · Accepted solution]

Hi,

yes. When the network type is p2p or broadcast, the node will send hello as soon it comes up an so the neighbor state will go to INIT or DOWN and so will reset the timer.

-Nagendra

[netops044]

Hello,

Thanks for update.

Why customer end device OSPF neighbor flapping frequently ????What could be the reason for OSPF flapping? where as  provider end not observed flap.

[Nagendra Kumar Nainar]

Hi,

If the link on CE goes down (on which OSPF is running), it is expected that the OSPF neighbor state entries over the flapped link will be cleared. But if the link on PE is stable, it will wait for OSPF dead interval before clearing the details. So within this time, if the CE link comes up, it might not clear the entries on PE side as we discussed above.

-Nagendra