ospf nei is flapping contiously

[sukkoor17]

Hi All,

There is an OSPF neighbour continuously changing state between Down and Full. 

I have configured the ip sec tunnel on both ends. Has anyone ever experienced this type of issue? please help to fix this issue.

I received the following output from log:

%LINEPROTO-5-UPDOWN: Line protocol on Interface Tunnel0, changed state to up

00:53:57: %OSPF-5-ADJCHG: Process 1, Nbr 172.16.1.2 on Tunnel0 from LOADING to FULL, Loading Done

%ADJ-5-PARENT: Midchain parent maintenance for IP midchain out of 0 65E900C0 - looped chain attempting to stack

%TUN-5-RECURDOWN: 0 temporarily disabled due to recursive routing

%LINEPROTO-5-UPDOWN: Line protocol on Interface Tunnel0, changed state to down

00:54:02: %OSPF-5-ADJCHG: Process 1, Nbr 172.16.1.2 on Tunnel0 from FULL to DOWN, Neighbor Down: Interface down or detached

%LINEPROTO-5-UPDOWN: Line protocol on Interface Tunnel0, changed state to up

00:55:12: %OSPF-5-ADJCHG: Process 1, Nbr 172.16.1.2 on Tunnel0 from LOADING to FULL, Loading Done

%ADJ-5-PARENT: Midchain parent maintenance for IP midchain out of 0 65E900C0 - looped chain attempting to stack

%TUN-5-RECURDOWN: 0 temporarily disabled due to recursive routing

%LINEPROTO-5-UPDOWN: Line protocol on Interface Tunnel0, changed state to down

00:55:17: %OSPF-5-ADJCHG: Process 1, Nbr 172.16.1.2 on Tunnel0 from FULL to DOWN, Neighbor Down: Interface down or detached

CORE-R1#

%SYS-5-CONFIG_I: Configured from console by console

%LINEPROTO-5-UPDOWN: Line protocol on Interface Tunnel0, changed state to up

[MHM Cisco World]

https://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/22327-gre-flap.html

I think you advertise tunnel source via Ospf with tunnel IP' that make tunnel and ospf flapping because tunnel know destiantion via tunnel itself'

As a rule you need two different igp one for tunnel itself and other for tunnel source/destination 

MHM

[sukkoor17]

Hi,

Thanks for your support now the issue is fixed.

Please let me know in what scenario the ospf state is stuck in the
loading state.

[Joseph W. Doherty]

---

@sukkoor17 wrote:
Hi,

Thanks for your support now the issue is fixed.

Please let me know in what scenario the ospf state is stuck in the
loading state.

---

Troubleshoot OSPF Neighbor Problems - Neighbor in Loading State

[Richard Burts]

Thanks for the update. Glad to know that the issue is fixed. What did you do to fix it?

I believe that the reference to " Midchain parent maintenance" is an indication that this is not the typical recursive routing that some of the responses have addressed. I had an experience with this when I was running an encrypted tunnel over a physical interface and running a dynamic routing protocol on the tunnel. The issue was that the physical interface would go down, the routing protocol had not yet detected the issue, attempted to send something which failed and generated the  Midchain parent maintenance. This link provides some additional information:

https://community.cisco.com/t5/routing/adj-5-parent-midchain-parent-maintenance-for-ip-midchain-eigrp/td-p/1169478

[MHM Cisco World]

Please let me know in what scenario the ospf state is stuck in the
loading state.

Sorry now the neighbor is stable but the ospf stuck in loading state? the main reason is the MTU mismatch between two OSPF neighbor 

Thanks

MHM

[Giuseppe Larosa]

Hello @sukkoor17 ,

>> %TUN-5-RECURDOWN: 0 temporarily disabled due to recursive routing

You are advertsing the GRE tunnel endpoints (external IP addresses source and destination) into OSPF over the tunnel itself you need to avoid this in order to have a stable tunnel and a stable OSPF adjacency over it.

You may want to use two different OSPF processes or even another IGP for the external IP addresses ( underlay) to avoid this.

Hope to help

Giuseppe

[paul driver]

Hello
Basic gre ospf tunnel - just DO NOT advertise any underlay transit addressing over the gre ospf tunnel

rtr1
router ospf 1
Router-id 100.100.100.1
int loop 0
ip address 1.1.1.1 255 255.255.255
Ip ospf 1area 0

int x/x
Ip address 10.1.12.1 255.255.255.252

int tun0
ip address 100.100.100.1 255.255.255.252
tunnel source  10.1.12.1
tunnel destination 10.1.12.2
Ip ospf 1 area 0

rtr2
router ospf 1
Router-id 100.100.100.2
int loop 0
ip address 2.2.2.2 255 255.255.255
Ip ospf 1area 0

int x/x
Ip address 10.1.12.2 255.255.255.252

int tun0
ip address 100.100.100.2 255.255.255.252
tunnel source  10.1.12.2
tunnel destination 10.1.12.1
Ip ospf 1 area 0

to simulate the recursion if you enable ospf on the 10.1.12.0/30 subnet you will see the same issue you are currently experiencing