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

[Richard Mikisa]

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