[c-nsp] OSPF flapping between Nexus 7000 and ASR 1001x

[Nick Cutting]

Is that a dark fiber P2P or a an ISP provided "L2 over L3 P2P"?  
If it's the latter like an eLine link - could they be re-routing traffic on their underlay where the mtu changes maybe?

-----Original Message-----
From: cisco-nsp <cisco-nsp-bounces at puck.nether.net> On Behalf Of Richard Mikisa
Sent: Tuesday, July 9, 2019 11:58 AM
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] OSPF flapping between Nexus 7000 and ASR 1001x

This message originates from outside of your organisation.

Hi All,

I am running OSPF across a point to point link between a Nexus 7000 and an ASR1000x.

The OSPF works fine but every couple of hours, it breaks and neighbor state goes into EXCHANGE and remains there for another 40 minutes or so. It then goes into full, OSPF comes up and all is well for another couple of hours or so and then the cycle starts again. All the time, IP connectivity between the two point to point IPs is up.

Configuration as below..

ASR1001x#sh run int g0/0/1
interface GigabitEthernet0/0/1
 description ** MPLS London -  SO031732 **  mtu 9216  ip address 10.32.250.17 255.255.255.252  ip ospf network point-to-point  ip ospf mtu-ignore  negotiation auto  cdp enable end

ASR1000x#sh ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
40.1.1.1          0   EXCHANGE/  -    00:00:33    10.32.250.18
GigabitEtherne
                    t0/0/1
10.32.8.253       1   FULL/DR         00:00:32    10.32.250.1
GigabitEtherne
                    t0/0/0


On the Nexus
N7K1-LON-AGG# sh run int vlan 3960

interface Vlan3960
  no shutdown
  mtu 9216
  ip address 10.32.250.18/30
  ip ospf cost 1
  ip ospf network point-to-point
  no ip ospf passive-interface
  ip ospf mtu-ignore
  ip router ospf 100 area 0.0.0.32

N7K1-LON-AGG# sh ip ospf neighbors 10.32.250.2  OSPF Process ID 100 VRF default  Total number of neighbors: 15
 Neighbor ID     Pri State            Up Time  Address         Interface
 10.32.250.2       1 EXCHANGE/ -      00:05:06 10.32.250.17    Vlan3960
N7K1-LON-AGG#

And the logs on the ASR

Jul  9 14:33:00.682: %OSPF-5-ADJCHG: Process 100, Nbr 40.1.1.1 on
GigabitEthernet0/0/1 from FULL to DOWN, Neighbor Down: Too many retransmissions Jul  9 14:34:00.683: %OSPF-5-ADJCHG: Process 100, Nbr 40.1.1.1 on
GigabitEthernet0/0/1 from DOWN to DOWN, Neighbor Down: Ignore timer expired Jul  9 14:34:46.962: %CLNS-5-ADJCHANGE: ISIS (Overlay1): Adjacency to N7K1-LON-OTV (Overlay1) Down, hold time expired Jul  9 14:39:56.543: %OSPF-5-ADJCHG: Process 100, Nbr 40.1.1.1 on
GigabitEthernet0/0/1 from EXCHANGE to DOWN, Neighbor Down: Interface down or detached Jul  9 14:55:20.865: %OSPF-5-ADJCHG: Process 100, Nbr 40.1.1.1 on
GigabitEthernet0/0/1 from EXCHANGE to DOWN, Neighbor Down: Interface down or detached .Jul  9 15:06:25.955: %OSPF-5-ADJCHG: Process 100, Nbr 40.1.1.1 on
GigabitEthernet0/0/1 from EXCHANGE to DOWN, Neighbor Down: Too many retransmissions .Jul  9 15:07:25.955: %OSPF-5-ADJCHG: Process 100, Nbr 40.1.1.1 on
GigabitEthernet0/0/1 from DOWN to DOWN, Neighbor Down: Ignore timer expired .Jul  9 15:37:57.514: %OSPF-5-ADJCHG: Process 100, Nbr 40.1.1.1 on
GigabitEthernet0/0/1 from LOADING to FULL, Loading Done .Jul  9 15:38:03.296: %CLNS-5-ADJCHANGE: ISIS (Overlay1): Adjacency to
8478.AC22.FEC3 (Overlay1) Up, new adjacency .Jul  9 15:42:25.399: %SEC_LOGIN-5-LOGIN_SUCCESS: Login Success [user:
richard.mikisa] [Source: 10.0.1.2] [localport: 22] at 15:42:25 UTC Tue Jul 9 2019


Can someone advise on where to look?
--
cheers
Richard
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