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

[adamv0025 at netconsultings.com]

Try removing the "ip ospf mtu-ignore" from both ends -see if the adjacency
comes up (past exchange).
Try enabling debug to see what exactly is going on -you should see straight
away what the crux of the problem is. 

adam
> -----Original Message-----
> From: cisco-nsp <cisco-nsp-bounces at puck.nether.net> On Behalf Of Richard
> Mikisa
> Sent: Tuesday, July 9, 2019 4:58 PM
> To: cisco-nsp at puck.nether.net
> Subject: [c-nsp] OSPF flapping between Nexus 7000 and ASR 1001x
> 
> 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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